Folia Geobotanica 33: 241-316, 1998 AN ACCOUNTOF THESPECIES OF POTAMOGETON L. (POTAMOGETONACEAE) Gerhard Wiegleb1) & Zdenek Kaplan2) 1) Department of General Ecology, BTU Cottbus, POB 10 13 44, D-03013 Cottbus, Germany; tel. +49 355 692291, fax +49 355 692291, E-mail wiegleb@tu-cottbus.de 2) Institute of Botany, Academy of Sciences of the Czech Republic, CZ-25243 Pruhonice, Czech Republic; fax +420 2 67750031, E-mail kaplan@ibot.cas.cz Keywords:Descriptions,Hybrids,Key to species,Specieslist, Synonyms,Taxonomicproblems Abstract:An accountof thetaxonomyof thegenusPotamogetonL. withspecialreferenceto speciesdescription anddelimitationis presented.A key to the species is given, basedas faras possibleon vegetativecharacters. Detaileddescriptionsare providedfor a total of 69 species which are regardedas sufficientlywell known. Specialemphasisis laid both on a completelist of relevantcharactersas well as on the judgementof their respectivediagnosticvalues.All importantsynonymsarelistedallowingdirectaccess to mostof the relevant taxonomicandfloristicPotamogetonliterature.50 confirmedhybridsare listedandassignedto theirputative parentspecies.Questionswith respectto the taxalistedareformulatedin noteson eachof the species.A more generalview andquestionson futurePotamogetonresearchare summarizedin the conclusions. "It is to be regretted that we never arrive to the truth but through some mistake or another" (J.O. Hagstrom 1916) INTRODUCTION Since the days of GRAEBNER (1907) and HAGSTROM (1916) no comprehensivetaxonomic treatmentof the genus Potamogeton L. claiming worldwide validity has been carriedout. The work of GRAEBNER (1907) was an attempt to compile all the known taxonomic and phytogeographicinformationaboutthe genus, althoughP. Graebnerhimself never carriedout importanttaxonomic work on the genus Potamogeton.In contrast,J.O. Hagstrom'streatment was based on 15 years of intensive anatomicaland morphologicalstudies of all specimens accessible to him. Hagstrom examined ca. 90% of the species known at that time. The comprehensiveness of his work is still unrivalled. Hagstrom's approach to infrageneric classification and species circumscriptionwas acknowledgedonly recently both by WIEGLEB (1988) and LES& SHERIDAN & (1990b). Anotherearly 20th centuryauthor,A. Bennett,had a worldwideknowledge of the genus, but he never produceda comprehensivetreatment.His work is scatteredin numerous,often contradictory,notes. Since the time of Hagstrom'swork a lot of new informationhas become available.Several papers deal with various aspects of the genus. Seed anatomywas treatedby AALTO (1970), general morphology by TOMLINSON (1982), chromosome numbers by LES (1982) and HOLLINGSWORTH et al. (1998), pollen morphologyby SORSA (1988), stem anatomyby WIEGLEB (1990c), and flavonoid chemistryby LES& SHERIDAN (1990a). However, the informationon 242 G. Wiegleb&Z. Kaplan species distributionand variation in different parts of the world is still quite inconsistent. Westernand CentralEuropeanPotamogeton taxonomy had reached a certain stability at the end of the 19th century.The work of PRESTON (1995) for the British Isles can be regarded as a culmination of this tradition in the degree of precision and completeness. In North America (FERNALD1932, OGDEN 1943, HAYNES1974, REZNICEK& BOBBETTE1976) and Japan(MIKI1937) a state of knowledge comparableto Europehas been reached.In Australia (ASTON 1973), South America (TUR 1982), South Africa (DANDY 1937, OBERMEYER 1966, SYMOENSet al. 1979), and Russia (YUZEPCHUK1934, TZVELEV1987, KASHINA 1988, VOLOBAEV 1993) a significant effort has been made without, however, solving important taxonomicandnomenclaturalproblems.Worldwideinformationon distributionandtaxonomy is only available for five of the widespreadspecies (HAYNES 1985, WIEGLEB 1990a,b). The following treatmentis regardedas a first step towardsa worldwide monographof the genus Potamogeton. The aims are to constructa key to all "sufficientlyknown species" and to give descriptions, as comprehensive as possible, for all those species according to the presentstate of knowledge. In additionquestionsareformulatedas a basis for futureresearch. METHODS Data base An assessment of the validity of the taxa recognizedbelow is based on the following work that has been conducted since 1985: (1) Herbariumstudies. Extensive herbariumstudies were carriedout in the course of the description and re-evaluation of several Potamogeton taxa (KADONO & WiEGLEB1987, WIEGLEB 1990a,b, 1993), the work in connection with Flora Malesiana (WIEGLEB, unpubl.) and the work on the contributionof Bohemianbotaniststo Potamogeton taxonomy (KAPLAN 1997). Additionalstudies were carriedout directlyfor the purposeof this paper.Potamogeton of B, BM, BREM, BRNM, BRNU, CTES, GLM, HBG, JE, K, L, M, MP, OLD, OLM, OP, PR, PRC, ROST,W, and WU were checked completely,and additionalloans were made from A, AAU, ABD, BKF, BOL, BP, BRI, C, CANB, CGE, E, F, G, GAT,GOET,H, HAL, LAE, LD, MICH, MO, NH, NY, P, PERTH,PH, S, SING, TAA, TAI, TFC, TI, TUB, U, UC, UPS, WAG, WRSL, and ZT. (2) Field surveys. The collection of specimens was carriedout in variouspartsof the world (G. Wiegleb: the Atlantic Islands, Western,Central and SouthernEurope, including Great Britainandthe MediterraneanIslands,Japan,Argentina;Z. Kaplan:Western,Central,Southern and EasternEurope, Siberia, SouthwesternAsia). Specimens are deposited in the herbariaof the respective authors(G. Wiegleb: Museum fiir Naturkundeund Vorgeschichte,Oldenburg, Germany;Z. Kaplan:Instituteof Botany, Pr'uhonice,Czech Republic). (3) Field ecological studies.The variationof varioustaxa(G. Wiegleb:P alpinus,P. natans, P. distinctus, P. wrightii; Z. Kaplan: P. pusillus, P. trichoides, P. pectinatus) was studied, including also experimental studies (KAPLAN,unpubl. data). (4) Studyof stem anatomy.The stem anatomyof varioustaxawas studiedin detail(WIEGLEB 1990c). The collection of slides with preservedcross sections is kept at the biological collection of the BrandenburgischeTechnische Universitat,Cottbus. (5) Literaturesurvey. Based on the data bases accumulatedindependentlyby both authors in the course of this survey,more than 2000 names were checked for their validity,legitimity, correct spelling and exact citation (Z. Kaplan). Taxonomyof Potamogeton 243 Taxonomic concepts An open discussion on the respective taxonomicconcepts at each level of the taxonomical hierarchyis regardedas crucial for a successful approachto Potamogeton. Delimitation of the genus In the present paper Potamogeton L. is regarded as one of two genera of the family Potamogetonaceae, the second one being the closely related genus Groenlandia J. GAY. Groenlandiadiffers from Potamogeton in the following aspects: (1) Fruittype (having a drupe-like,instead of an achene-like, fruit in Potamogeton). (2) Specialized type of hibernatingstructures(not found among the numerous types of winter buds in Potamogeton). (3) Predominanceof subopposite leaves throughoutthe stem (in Potamogeton occurring in the floral region only). (4) Absence of stipule-like appendages(subsequentlyreferredto as "stipules")on most of the leaves with lateralones being producedonly on the involucralleaves (Potamogetonhas axillary or adnate stipules on all leaves). (5) Spikes bearingregularly(1-)2(-4) flowers only (comparedwith the 4 to many-flowered spikes of Potamogeton). (6) The uniquebasic chromosomenumbern= 15 (comparedwith n= 13 or rarelyn=14 found in Potamogeton). Classification into subgenera Recently, several attemptshave been made to introducea thirdgenus Coleogeton (RCHB.) LEs et R.R. HAYNES(LES & HAYNES1996), or more correctly Stuckenia BORNER(HOLUB 1997), based on a group of species formerlytreatedas subgenusColeogeton (RCHB.)RAUNK. However, the reasons for separatingthis groupfrom the genus Potamogetonare not regarded as convincing. Most of the charactersclaimed to be exclusive for Stuckenia occur also in Potamogeton s.str.: (1) Stipularsheaths, mostly fused for more than half of their length. Stipularsheaths are constantly found in P. spirillus (in this species the fused portion is also longer than half of the length), P diversifolius, P. bicupulatus,P. robbinsii and P maackianus, also in young specimens of P alpinus, P. nodosus, P. distinctus,P wrightii, P gramineus and P. lucens. (2) Channelled leaves (phyllodial leaves sensu RAUNKIAER 1896). Such kinds of leaves are, however, regularlyproducedin P. natans, P oakesianus, P. diversifolius,P bicupulatus, P. spirillus, P. octandrus, P. cristatus, P vaseyi, often also in P lucens, P. gramineus, P thunbergiiand P. illinoensis. This holds even though "phyllodial leaves" cover a wide range of leaf shapes. (3) "Hydrophilouspollination".Pollination in Stuckenia, as inferred from the elongated stigma, is claimed to be differentfrom "anemophilous"pollinationin Potamogeton.However, epihydrophily(includinghydroautogamy;i. e. pollinationby means of two dimensionalpollen transferrestrictedto the water/airinterface,eitherat the watersurfaceor on bubblesproduced by submersedflowers during anthesis) occurs also in P acutifolius, P pusillus, P foliosus and P lucens, all of them being member-sot Potaitnogetons. str. (4) Higher ploidy level (particularlyhexaploidy).The distinctionin chromosomenumber is not so clear as is sometimes stated. Higher ploidy levels have also been reportedfor P crispus, P illinoiensis and P richardsonii. 244 G. Wiegleb&Z. Kaplan (5) Hybridization. It is said not to occur between Stuckenia and Potamogeton. The taxonomicallyunclearplant describedas P. nomotoensismay be a hybrid between members of these respective taxa (P. natans and P. pectinatus), as it combines the typical characters of both groups. We are aware that Coleogeton (Stuckenia)representsa compact monophyletic unit which differsfromPotamogetonin several charactersrelatedto floral biology (endodermisof U-type in the flexible peduncle, elongated stigmas, specializedpollen type) and hibernation(forming a special type of rhizomatousturion).However,we drawattentionto the fact thatthe endocarp type A is found in both taxa (AALTO1970). As we consider the charactersused by LES& HAYNES (1996) andHOLUB (1997) as insufficientfor genericdistinction,the traditionalconcept of treatingColeogeton at the rank of a subgenus is adoptedhere. Infrageneric classification and arrangement of species The arrangementof species in the descriptivepartreflectstheirsupposedsystematicrelation. It is based on cladistic analyses of all taxa based on the charactersavailable so far (KAPLAN, unpubl.). Assumptions on the affinity of the species are generally outlined in the notes. No formal groupingis adopted. We are aware of the fact that a taxonomic revision at the level of sections and subsections is also desirable. However, it cannot be carried out at present. Depending on the exact delimitationof these taxa, a complete check of the nomenclaturehas to be carriedout. We assume that the genus Potamogeton may be furthermoredivided into 5 sections, 1 in Coleogeton and 4 in Potamogeton, which form naturalunits. The approximatenumberof subsections is 22, 3 in Coleogeton and 19 in Potamogeton. Species concept A wide species concept is adopted in the following treatment.All Potamogeton species studied in more detail so far with respect to vegetative morphology and life history exhibit a wide range of phenotypic plasticity. It is presumedhere that this holds also for the rest of the species. Therefore,the distinctionof a species requiresat least two independentcharacters which remain stable over a largergeographicalarea and over a wide range of environmental conditions. Species with a limited geographicalrange differingby single charactersfrom an otherwise variable species are generally not recognized. In some cases of broad-leavedspecies, taxa with a limited geographicalareaarerecognized as they exhibit uniquecharactercombinations (e.g. the southernspecies P. stenostachys,P parmatusand P. papuanicus). In total 69 species are recognized and described. Unfortunatelythe total range of plasticity of most species of the SouthernHemisphereis unknown. Concepts of infraspecific units A generalconcept of a taxonomic treatmentof infraspecificclassification has not yet been developed. Most varieties and forms recognized by older authors refer to obvious ecomorphoses and have no taxonomic value whatsoever.Exceptionally,they are important insofar as they contain basionyms for the modern treatment. However, some of the taxonomic entities mentioned in the synonym list with a question mark, or in the notes which follow the descriptions,may be regardedin the future either as allopatricsubspecies or as sympatricvariantsof the respective widespreadtaxon. Taxonomy of Potamogeton 245 Hybrid concept Hybridizationis, under certain circumstances,a frequentevent in Potamogeton and often leads to easily recognizable biological entities. Because of their frequency and ecological importance(WIEGLEB 1988) they have to be considered in any taxonomic treatmentof the genus. Neglect could lead to misidentificationof a numberof specimens. In total 50 hybrids are recognized here as being well establishedand distinguishablefrom the respective parent species. Approximately20 furtherprobable hybrids proposed in the literaturecannot be recognized without furtherstudy, in particularby experimentalcrossing experiments. Many proposed hybrids, of which we were able to study the type specimen, proved to representone of the parentalspecies only. The correctnames of the hybridsare based on both putativeparentspecies. Synonyms and notes are only given after the first-mentionedparent species. No descriptionof the hybrids is given, as in most cases the hybrids are intermediateamong the putative parents.We are aware of the fact that this is not true in all cases. Our list of "hybrids"contains three groups of taxa, which cannot be operationallydistinguished: (1) Confirmedhybrids, most probablyof recent origin, which are usually sterile, forming no seeds, or at least no viable seeds (e.g. P. xnitens), or only exceptionally producingwell developed fruits (best known in P. xangustifolius).We assume that this is the most frequent case. (2) Fertile intermediatesthat may in the future be regardedas species in their own right, which are possibly of hybridogenousorigin in the past. P. xogdenii is the only memberthat can be named at present. This case underlinesthe possible importanceof hybridizationfor species formationin Potamogeton. (3) Some special forms which are too rare to be judged finally, and which clearly do not deserve the rank of a species. The identity of these forms has to be clarified in the future. P. xnomotoensis,P xvaginans and P. xfaxonii belong to this group. All hybrids of the second and thirdgroup are commentedupon in a respective note. The key The accountof the species is precededby an analyticalkey to the species. The mainpurpose of the key is to elucidate the most importantcharactersthat are useful for distinguishing between the species. Thus, the key providesa kind of definitionand delimitationof the species considered as valid in the frameworkof this treatment.The key is an artificialone. It is not intendedto key out assumed subsections or relatedspecies groups in total before proceeding to the species themselves. The key should enable the user to identify most of the species based on the typical variation shown by their individuals, provided that the necessary diagnostic charactersare developed on a specimen examined. The key cannot be used to identify all extreme morphotypes,nor can it give access to incomplete and fragmentaryherbariumspecimens. As far as possible, it is based on charactersof vegetative morphology,in particularshape, size, and venationof the submergedleaves. These are the charactersthat are available in most cases. 246 G. Wiegleb & Z. Kaplan An account of the species General arrangement of characters The structurefollows the general patternas listed below: (1) Name (2) Citation (3) Importantsynonyms (4) Rhizome:shape,life cycle (5) Stem:shape,life cycle (6) Submergedleaves:lamina:shape,size, colour,venationandotherspecialfeatures;petiole (7) Intermediate leaves (if developed);shortcharacterization (8) Floatingleaves (if developed):lamina:shape,size, venationandotherspecialfeatures;petiole (9) Stipules:shape,size and specialfeatures(if necessaryseparatefor leaf types) (10) Peduncles:size and shape (11) Spikes:shapeand size (if necessaryseparatefor spiketypes) (12) Flowernumber;numberof carpels (13) Fruits:size, specialfeatures (14) Stem anatomy:stelartype, endodermistype, interlacunar bundles,subepidermal bundles,pseudohypodermis (15) Distributionin outline (16) Hybridsincludingtheirimportantsynonyms (17) Notes The list of synonyms is restrictedto those used in importantfloras or reference works as accepted by the respective authors. For example, most taxa treated at the species level in GRAEBNER(1907) and HAGSTROM(1916) can be assigned to species we recognize. Furthermore,names generally cited and names published in recent years are recognized. In order to save space, the list is confined only to "moreimportant"names, mostly at the level of a species. Names of subspecies are sometimes included as they are generally neglected, but may become importantfor future infraspecific treatment.In the case of an uncertain assignment of a name a question mark is added. The description of morphology and anatomy is carried out with special emphasis on vegetative diagnostic characters.The descriptive terms of morphology, population biology and anatomy are outlined below. The notes usually concentrateon two importantquestions: Does the respective taxon exist and which is the correctname? What informationis lacking to answer these questions? Information excluded The following items were deliberatelyexcluded from the account of the species: (1) Informationon typification and the deposition of type specimens. Types are often not designated, and in case of designation contradictoryinformationis available in many cases. This implies a certain instability of nomenclature. (2) Chromosome numbers. Overviews of published chromosome numbers can be found in LES(1982) and more recently in HOLLINGSWORTH et al. (1998). The data are excluded from the descriptions for several reasons. Only for ca. 30 species are two or more methodologically reliable counts available. All reliable counts originate from the Northern Hemisphere. Of at least 20% of the reliable counts we are not sure to which taxon of the present treatmentthey actually refer. Taxonomy of Potamogeton 247 (3) Further information about several floral and generative characters, which have been regarded as important by earlier authors, e.g. information about sepaloid connectives or additional information about size, shape, and colour of fruits. Descriptive terms of vegetative morphology Descriptions of morphological characters and life histories in the taxonomic treatment of Potamogeton are often inexact. This is due to the fact that all Potamogeton species have a complex modular organization difficult to describe both in terms of classical and functional morphology. A fully satisfactory description of all morphological characters regarded as taxonomically important would be very space consuming. If possible, the nomenclature on branching, longevity of plant parts, overwintering structures, seasonality, etc. as proposed by BRUXet al. (1989), WIEGLEB & BRUX(1991), and WIEGLEB& KADONO(1989a,b) is adopted. As some simplifications were necessary, some explanations are given below. Shoot types. In Potamogeton two different basic shoot types occur, namely "vertical shoots" [VS] ("erect shoot" sensu TOMLINSON1982, including also the lateral "renewal shoots") and "horizontal shoots" (as lower and upper horizontal shoots [LHS, UHS]), which differ in leaf insertion and vegetative anatomy (TOMLINSON 1982). This differentiation is visible in all species, despite the fact that individual plants can change their growth pattern in an opportunistic way. Only for the sake of comparability with general Potamogeton literature do we use the term "rhizome" in the descriptions for the lower horizontal shoot, regardless whether it is actually stoloniferous, rhizomatous, or a complex of differently shaped parts. In the descriptions we also use the term "stem" characterizing the main axis of the vertical shoot. If necessary we use the terms "horizontal shoot" and "vertical shoot" to remain morphologically exact. Branching pattern. A complete account on branching pattern cannot be given here, as even terms like "sympodial" and "monopodial" are not well-defined in Potamogeton and would require explanation at length. If we use expressions like "stem unbranched" we indicate that the species (e.g. P. alpinus) develops no renewal shoots below the pseudo-opposite involucral leaves. But it may produce turion-bearing upper horizontal shoots in some cases, in particular at the end of the growing season. In principle, branching analysis is also important for a proper description of the inflorescence types. As the "inflorescence types" sensu HAGSTROM (1916) are not known for all species, we do not mention them. We use simple descriptive terms like "apical" or "lateral" to characterize the position of flowering parts, well knowing that these terms are imprecise without having identified the primary spike. In accordance with TOMLINSON (1982) we use the term "inflorescence" for the "spike-peduncle unit" as a whole. This contrasts with HAGSTROM'S (1916) use of this term. Longevity and hibernation. We avoid undifferentiated expressions like "annual" and "perennial". Terms relating to longevity always refer separately to below-ground or above-ground parts of an individual. Additionally, remarks on seasonality are given, if information is available. For example, in P lucens the rhizomatous part of the LHS is at least biennial, mostly perennial, while the above ground vertical shoots are often short-lived and summer-green. The species has a seasonal development throughout its range. Unfortunately, such information is in most cases not available for Southern Hemisphere species. We distinguish various types of "winterbuds" or "propagules" (see RAUNKIAER1896), which in all cases serve several functions in the life cycle of an individual plant (hibernation, 248 G. Wiegleb & Z. Kaplan droughtresistance,shortrangedispersal,etc.). We distinguishbetween winterbudson vertical and horizontalshoots: (1) Winterbudson VS are found as axillaryor apical fusiform "turions",which are mostly dormant (e.g. in P. pusillus), as non-dormantaxillary turions of varying shape (e.g. in P. crispus), or as unspecialized, non-dormant,axillary, short shoots (e.g in P. natans and P. praelongus). (2) Winterbudson LHS are found mostly as dormant apical turions on stoloniferous horizontalshoots (e.g. in P. alpinus, also on upperhorizonatalshoots), as rhizomatoustubers (e.g. in P.pectinatus), and as turion-tubercomplexes, mostly on rhizomatouslower horizontal shoots (e.g. in P. lucens). Also unspecializedleafy verticalshoots can be regardedas winterbuds in some species (e.g. in P. amplifolius). Leaf description. Special emphasis is paid to the descriptionof the leaves. Descriptive terms of leaf structureare always expressed in comparisonto other aquaticplant leaves (and not terrestrialmesophyte leaves, as is often found in the literature).The fact that submerged leaves are membranousand translucentis taken for granted.The typical submergedleaf is found in the middle of the stem. The lower submergedleaves are often different in shape, which is acknowledged if they make up a significant portion of the leaves. The upper ones are often developed as "intermediate leaves". These leaves can be independently "intermediate"between submergedand floating leaf as to shape, structure,and petiolation. They may sometimes be presentin the absenceof truefloating leaves. This fact usuallyresults from a phenotypicreaction to varying water levels. Descriptive terms of stem anatomy We regardstem anatomicalcharactersas useful informationwith respect to the taxonomic arrangementof the species, and also the identificationof fragmentaryherbariumspecimens (see HAGSTROM 1916, TUR 1982, WIEGLEB1990c). However,the anatomicalcharactershave to be treatedwith great care. There is a lot of variationwithin species, often even within one individualspecimen. Particularlyin the studyof herbariumspecimens, when only those shoot types and parts available by chance can be studied, results of the study of a single cross section must not be overestimated. The stem anatomical charactersreportedhere refer to internodes on the upper parts of stems. The following charactersare regardedas taxonomicallyimportant: (1) Type of stele, distinguishingamong the proto type (with more than 8, usually 10-14 free vascular bundles), the trio type (or eight bundles type, if necessary with additional informationon the numberof phloema, 1 or 2, in the trio bundle), the oblong type (with the 3 separatedparts themselves containing 1-3 bundles), the four bundles type, and finally the circular type (or one bundle type). In a few cases additional characters like shape and sclerenchymatizationof the stele are listed. (2) Cell shapeof the endodermis(which is eitherof U or 0-type, or intermediateU-0-type). A furtherpossible differentiationaccording to the strengthof the cell walls is attributedto the developmentalstage of the individual. (3) Presence of interlacunarbundles, with additional informationon number (including completeness of rings) and size. (4) Presence of subepidermalbundles, including numberand size. (5) Presence of the pseudohypodermis,including numberof cell layers. Taxonomy of Potamogeton 249 KEYTO THESPECIES la lb 2a 2b 3a 3b 4a 4b 5a 5b 6a Stipulesof submergedleaves adnatefor most of theirlengthto the leaf base, leaf laminaarisingat the top of the stipularsheathwhich surroundsthe stem abovethe node;submergedleaves alwayslinearto broadlylinearor rarelylanceolate............................ 2 Stipulesfree from the leaf base or almost so, leaf laminaor petiole arisingdirectlyfrom the node; submergedleaves linearto broadlyovate........................... 13 Leaves serrulateor denticulateat margins,1.1-8.0 mm wide, 7-25 times as long as wide, auriculateto roundedat the base............................................................. 3 Leavesentireat margins,0. 1-2.5(-5.0) mm wide, 15-600 timesas long as wide, straightat the base. . 4 Submergedleaveslanceolate,graduallytaperingto apex,stiffish;specializedaxillaryandapicaldormant turionsdeveloping;scatteredinterlacunar bundlespresent...... 36. P. robbinsii ................ Submergedleaves linear,with ? parallelmargins,abruptlytaperingat apex, ? lax; specializeddormant turionsnot developing;interlacunar bundlesabsent...... 37. P maackianus ................... Stipules fused with the leaves for 6-65(-140) mm; floating leaves always absent; inflorescences monomorphic; peduncles20-200(-450) mmlong;spikeslong cylindrical,(13-)20-75 mmlong in fruit; submergedleaves tubularwith airchannelsborderingthe midrib;fruitsconvex on sides, withoutlateral keels;endodermisof U-type,rarelyof 0-type ........... ............................... 5 Stipulesfused with the leaves for 0.3-6.0 mm;floatingleaves often present;inflorescencesdimorphic to trimorphic;peduncles 1-32 mm long; spikes subgloboseto cylindrical,2-28 mm long in fruit; submergedleaves ? flat with lacunaeborderingthe midrib;fruitsconcaveon sides, with distinctlateral keels;endodermisof 0-type .1...................................................... 1 Stipulesconnateandtubularat the base whenyoung,marginsof the openportionbrown;flowerwhorls in spikemarkedlyremoteat anthesis;leavesof the mainstemobtuseat apex;maturefruits(1.9-)2.2-3.5 mmnlong ............................................................ 6 Stipulesopen andconvolutealongtheirentirelength,marginsof the openportionwhitish;flowerwhorls in spikecontiguousat anthesis,laterremote;leavesof themainstemacuteto obtuseor subretuseat apex; maturefruitsmostly 3.0-4.7(-5.1) mm long ........... ................................ 7 6b Leaves0.3-1.2(-1.9) mm wide, (50-)100-300 timesas long as wide, obtuseto subacuteon side shoots; fruits(1.9-)2.2-2.8(-3.2) mm long; apex of ligule obtuseto rounded;stipularsheathof leaves on main stemnot inflated.............. 66. P filiformis Leaves 1-3 mm wide, 20-50 times as long as wide, always broadlyobtuse;fruits(2.8-)3.0-3.5 mm long;apex of ligule subretuse;stipularsheathof leaves on mainstem ofteninflated. ............................................................... P67.Pamblyphyllus 7a 7b Leavesalways obtuseto subretuse;fruitswithouta distinctbeak........................... Leavesmostlyacuteto acuminate;fruitswith a distinctbeak .. 8a 8b Leavesstronglyrecurvedat the top;pedunclesshort,20-50 mm long .... ........ 65. P recurvatus Leavesnot recurvedat the top;peduncles30-170(-200) mm long.......................... 9 9a Leavesobtuseat apex;peduncles30-150 mm long; stipularsheathof leaves on mainstem(especially the lower ones) very broad,up to 10 mm wide, 30-70 mm long; interlacunarbundlesin (3-)4 circles 63. P vaginatus ................................................................. At least some leaves clearly subretuseat apex;peduncles100-170(-200) mm long; stipularsheathof leaves on main stem narrower,1.5-4.0 mm wide, 20-30(-40) mm long; interlacunarbundles in 1 incompletecircle .......... 64. P subretusus 9b 8 10 lOa Leaves of the main stem less thantwice as wide as those on the branches;fruitswith a beakup to 1.2 mm long, rhizomatoustubersmostlydeveloping.......... 68. P pectinatus lOb Leavesof the main stem morethantwice as wide as those on the branches;fruitswith a beak less than 0.5 mm long;rhizomatoustubersnot developing........ 69. P striatus 250 G. Wiegleb & Z. Kaplan 1la (4) Adnateportionof the stipulemostlylongerthanfree ligule, fused with the leaves for 1.5-6.0 mm; fruitswith a dorsalkeel and smoothlyroundedsides, lateralkeels absent..... ....... 60. P spirillus 1lb Adnateportionof the stipulemostly shorterthanfree ligule, fused with the leaves for 0.3-3.5(-4.0) mm;fruitsusuallywithtwo lateralentireto dentatekeels in additionto the dorsalkeel .... ...... 12 12a Submergedleavesfromthe middlepartof stem(0.3-)0.5-1.5 mm wide, 20-180 timesas long as wide, floatingleaves (7-)13-40 mm long ....... 61. P diversifolius ................. 12b Submergedleavesfromthe middlepartof stem0.1-0.4(-0.5) mmwide, 190-500 timesas long as wide; 62. P bicupulatus floatingleaves 6-23(-28) mm long........................ 13a (1) Leaf marginsserrate,with teetheasily visible to the nakedeye; fruitsadnateat base;beak at least half as long as the rest of the fruit;submergedleaves (3-)5(-7)-veined; floatingleaves alwaysabsent . 35. P crispus ................................................................ 13b Leaf marginsentireor minutelydenticulate,with teethnot or scarcelyvisible to the nakedeye; fruits freeatbase;beakmostlymuchless thanhalfas longas therestofthefruit;submergedleaves1-41-veined; 14 floatingleaves absentor present................................................... 14a All leaves filiformto linear,with parallelsides, or sometimeslinear-lanceolate, (13-)18-110 timesas long as wide, mostly0.1-6.0, rarelyup to 9.0 mm wide, all sessile, submerged,entireat margins;stele of oblongor circulartype (in P polygonus of protoor reducedtriotype).15 14b Mostlyall, butat least floatingleavesnarrowlyellipticalto orbicular,withconvex sides, 1-13 timesas long as wide, 4-80 mm wide, sessile and/orpetiolate,submergedand/orfloating(or rarelyemersed when semiterrestrial), entireand/ordenticulateat margins;stele mostly of proto,trio or four bundles type, sometimesof oblongor circulartype.33 l5a Leaveswithbothlateralveinsandmanyadditionallongitudinalsclerenchymatous strands;stemstrongly compressedor flattenedto terete;stele of oblongtype, rarely(P polygonus)of protoor reducedtrio type.16 15b Leaveswith 1-4 lateralveins on each side of the midribwithoutadditionalsclerenchymatous strands; stemtereteor subtereteto slightlycompressed;stele mostlyof circulartype, sometimesof oblongtype 24 .......................................................................... 16a Leaves (5-)7-9-veined, 3-6(-9) mm wide, with broadto very broadrows of lacunaeborderingthe midrib,acuminateat apex; strandsin the leaf margins stronglysclerenchymatous, persistingas fibres 38. P polygonus . ............................................................... 16b Leaves 3-5-veined (5-7(-9)-veined in P oxyphyllus),mostly 1.2-5.0 mm wide, with narrowrows of lacunae borderingthe midrib, acuminateor acute to obtuse, rounded or mucronateat apex; sclerenchymatous strandsin the leaf marginsalmostof the same strengthas the otherleaf veins . . 17 17a Leaves (1.8-)2.0-5.4(-6.0) mm wide, with 16-34 sclerenchymatous strands(only (2-)8-16(-20) in P oxyphyllus);fruits(2.8-)3.0-5.5 mm long......................................... 18 17b Leaves 1.2-2.5 mm wide, with 8-16(-20) sclerenchymatous strands;fruits2.1-3.5 mm long ..... 23 18a Stemterete,0.3-0.6 mm in diameterthroughoutthe shoot ............................... 19 18b Stem stronglycompressedto flattened,(0.4-)0.6-3.4 mm wide (in P compressusexceptionallyup to 4.8 mm wide), distinctlybroadenednearthe nodes.21 19a Leaves with (2-)8-16(-20) sclerenchymatousstrands, 5-7(-9)-veined, linear to narrowly linear-lanceolate, acuminateat apex;pseudohypodermis absent....... ............. 46. P oxyphyllus 19b Leaves with 20-32 sclerenchymatousstrands, (3-)5-veined, linear, acute to obtuse at apex; pseudohypodermis 2-3-layered.20 20a Leaves25-90(-130) mm long, obtuseat apex. 20b Leaves85-200 mm long, acuteat apex.40. . .39. P ochreatus P furcatus 21a Peduncles3-15(-26) mm long;spikesalmostglobose,4-8 mm long in fruit,with (I-)2(-3) whorlsof flowers;stipules10-21(-29) mm long;flowerswith l(-2) carpels...... ........... 41. P acutifolius Taxonomy of Potamogeton 251 21b Peduncles(19-)28-100 mm long; spikes cylindrical,15-33 mm long in fruit, with 5-11 whorlsof flowers;stipules(16-)20-55 mm long;flowerswith (1-)2(-3) carpels..... ................. 22 22a Fruitsobliquelyandnarrowlyobovatein outline,3.4-4.0 mm long,beakrecurved,leaves(3-)5-veined, stipulessoon erodingto fibrousstrandsat the apex .......... 42. P compressus ............... 22b Fruitsquadratelysuborbicular,4.0-5.0(-5.5) mm long, beak nearly erect, leaves 3-veined, stipules persistentandgenerallyintactthroughoutthe season......... 43. P zosteriformis ............... 23a (17) Leaves 1.5-2.5 mm wide, acuminate;fruits2.8-3.5 mm long;dorsalkeel distinct. 44. P manchuriensis .............................................................. 23b Leaves 1.2-2.0 mm wide, roundedand mucronateat the apex; fruits2.1-3.0 mm long; dorsalkeel indistinct.. . . 45. P sibiricus 24a (15) Rhizomelong andcreeping;inflorescence1 or rarely2 in terminalposition;peduncles15-240 mm 59. P. confervoides long;leaves filiform,0.1-0.5 mm wide................................. 24b Rhizomeshort or absent;inflorescencesusually more than 1 per shoot both in terminaland lateral position;peduncles3-70(-80) mm long;leaveslinear,rarelyfiliform,0.3-6.0 mm wide .... ..... 25 25a Leavesobtuseto roundedat apex,oftenvery shortlymucronate,oftenwitha reddishtinge;stemrichly branched;intermodes mostlymuchshorterthanthe adjacentleaves ........... 54. P obtusifolius 25b Leaves acute,acuminate,mucronateat apex or graduallytaperingto a fine, almostbristle-likepoint, reddishtingepresentor mostlyabsent;intemodesshorteror longerthanthe adjacentleaves. 26 26a Leavesregularly3-7(-9)-veined, (1.5-)2.0-6.0 mmwide;spikes9-17 mm long .27 26b Leavesregularly3-veined,rarelysome 5-veined,mostly0.3-2.0 mm wide;spikes3-11(-13) mm long ........................................................................... 28 27a Stipulessplit into two remnants,fusedat base, almostentirelyfree at apex;leavesdistinctlymucronate at the apex,with a faintmarginalvein, 1.5-3.5 mm wide;flowers4-8 in spike;fruits2.4-3.0 mm long 47. P friesii .................................................................... 27b Stipulesnot split into two remnants,convolute(fused on the side towardsto the leaf and free on the oppositeside); leaves acute at apex, with marginalstrandsstronger,remainingas fibres,(2-)3-6 mm wide;flowers5-12 in spike;fruits4.3-4.6 mm long.49. P gayi 28a Leaf midriboccupying 1/3-3/5 of the leaf width nearthe base, with stronglyconvex lower side in cross-section,not borderedby rows of lacunae;flowerswith 1(-3) carpels;leaves mostly0.3-1.0 mm wide.55. P trichoides 28b Leaf midriboccupyingup to 1/5 of the leaf widthnearthe base, with slightlyconvex lower side in cross-section,mostlyborderedby rowsof lacunae;flowerswith4(-5) carpels;leaves0.5-2.5(-3. 1) mm wide.29 29a Fruitswith a dorsalkeel up to 0.4 mm high,often with 2 lateralkeels;spikes2-7 mm long in fruit... . ........................ ........................................................................... 29b Fruitswithdorsalside rounded,lateralkeels alwaysabsent;spikes3-14 mm long in fruit.... .... 31 30a Fruitsconvex on sides, 2.3-4.0 mm long, 3-keeled;dorsalkeel ridge-like,to 0.2 mm high;peduncles 6-14 mm long .......................................................... 53. P hillii 30b Fruitsconcaveon sides, 1.4-2.7 mmlong, 1-keeled;dorsalkeel wing-likeandundulate,to 0.4 mmhigh; 52. P.foliosus pedunclesmostly 3-11 mm long.......................................... 31a Stipulesdelicate, not fibrous,greenish,brownor greenishwhite, translucentwhen dry, connateor convolute;leaves flaccid,acuteor acuminateat apex,not finely pointed..... ....... 48. P pusillus 31b Stipules(especiallythose of turions)firm,coarselyfibrous,whitish,opaquewhendry,connate;leaves rigid,graduallytaperingto a fine, almostbristle-likepoint,or sometimesacuteat apex ..... ...... 32 32a Leaves0.5-1.1 mm wide; spikes3-10 mm long;flowerwhorlscontiguous........... 50. P rutilus 32b Leaves0.6-2.0 mm wide;spikes6-13 mmlong;flowerwhorlsremote..... ....... 51. P strictifolius 252 G. Wiegleb & Z. Kaplan 33a (14) Submergedleaves narrowlylinear,0.1-1 .0(-l .9) mm wide; laminaof floatingleaves 3-11 mm wide. ............................................................ 34 33b Submergedleaves broadlylinearor ribbon-liketo broadlyovate,morethan2.5 mm wide, or phyllodial, 0.2-3.5 mm wide; laminaof floatingleaves, if present,morethan(7-) 1 mm wide ..... ........ 36 34a Fruitswithdorsalkeel stronglydevelopedandcristate,beakconspicuous..... ........ 57. P. cristatus 34b Fruitswith dorsalkeel entireor obtuselydentate,beakshort.............................. 35 35a Beak in ripe fruitsstraight;submergedleaves 0.5-1.2(-1.9) mm wide, 30-75 times as long as wide; floatingleaves acuteat apex, with petioles0.2-1.1 times as long as the lamina..... 56. P. octandrus 35b Beak in ripe fruits slightly recurved;submergedleaves 0.1-0.5 mm wide, 150-250 times as long as wide;floatingleaves obtuseat apex,withpetioles0.7-2.0 timesas long as the lamina.... 58. P. vaseyi 36a All submergedleaves consistingof narrowlylinearphyllodes,with a convex lower side, 0.2-3.5 mm wide, 70-300 timesas long as wide, lateralveins inconspicuous;floatingleaves almostalwayspresent, with laminaoblong to broadlyellipticalor broadlyovate;endodermisof U-type;interlacunar bundles alwayspresent........ 37 36b Mostor all submergedleaves withwell developedlamina,flaton bothsides, 1-80 mmwide,2-70 times as long as wide, lateralveins conspicuous;floatingleaves absentor present,with laminaof various shape;endodermismostlyof 0-type, sometimesof U-type;interlacunar bundlespresentor absent. . 38 37a Laminaof floating leaves 40-100(-140) mm long, (7-)20-45(-80) mm wide, 17-25(-35)-veined, usually subcordateat the base; submergedleaves 0.8-3.5 mm wide; fruits 3.8-5.0 mm long; pseudohypodermis presentin 1-2 layers............ 16. P. natans ................ 37b Laminaof floatingleaves(13-)22-40(-55) mmlong,(5-)10-22(-29) mmwide,(7-)9-19(-23)-veined, cuneateto roundedat the base; submergedleaves 0.2-1.0 mm wide; fruits 2.5-3.5(-3.7) mm long; pseudohypodermis absent,rarelypresentin I layer.......... 17. P oakesianus .............. 38a Submergedleaves with relativelybroadrows of lacunaeborderingthe midrib,linearto ribbon-like, delicate,flaccid, 1-1 mm wide, 14-70 times as long as wide, sessile except for the uppermostones . ................................................................ 39 38b Submergedleaves with relativelynarrowrows of lacunaeor completelywithoutlacunae,lanceolateor narrowlyellipticalto broadlyovate(lanceolateto ribbon-likein P.solomonensis),membranous, (2-)4-75 mm wide, 1.3-19.0(-21.0) times as long as wide, sessile or petiolate...... 41 ................. 39a Laminaof floatingleaves 14-31 mm long,6-9 mm wide,5-9-veined;submergedleaves 1-4 mm wide, 3-7-veined;inflorescencesregularlyinsertedintheaxilsof bothfloatingandsubmergedleaves;peduncles 11-27 mm long ......... 30. P ulei 39b Laminaof floatingleaves33-80 mmlong,7-25 mmwide,9-21-veined;submergedleavesusually3-11 mm wide, 5-9(-13)-veined; inflorescencesinsertedmostly in the axils of floatingleaves; peduncles 23-lO0 mm long ............ 40 40a Petiolesof truefloatingleaves not flattened,20-60(-90) mm long; submergedleaves persistent. .................................................................. 29. P epihydrus 40b Petiolesof floatingleaves flattened,40-115(-150) mm long; submergedleaves mostlydecayingearly 31. P montevidensis .............................................................. 41a Submergedleaves sessile, amplexicaulto semiamplexicaulat base, claspingthe stem;floatingleaves alwaysabsent. ................................................................ 42 41b Submergedleaves petiolateor sessile with cuneatebase, not claspingthe stem;floatingleaves present or absent.................................................................... 44 42a Leavesentireat margins,distinctlyhoodedat apex,60-360 mm long;fruits4.5-5.5 mm long; stele of prototype;endodermisof U-type,rarelyO-type;interlacunarbundles present,strong... 28. P praelongus 42b Leavesdenticulateat margins,notor onlyscarcelyhoodedat apex,mostly15-80 mmlong;fruits2.2-4.2 mm long; stele of specializedtriotype;endodermisof 0-type; interlacunar bundlesabsent....... 43 Taxonomy of Potamogeton 253 ........ 26. P.perfoliatus 43a Stipulesdelicate,withoutfibres,decayingearly;fruits2.2-3.5 mmlong ..... ............. 27. P richardsonii 43b Stipulesfibrous,persistingas fibres;fruits2.7-4.2 mm long ..... 44a All truesubmergedleaves sessile or sometimesveryshortlypetiolate,withpetiolesless than5 mmlong, leavesmayhavemuch 0.00-0.05 timesas long as the lamina,the uppermostsubmergedor intermediate 45 .................................... longerpetioles ............... 44b Mostorall submergedleavespetiolate,withmostorall petiolesatleast(3-)5 mmlong,(0.03-)0.05-5.00 49 timesas long as the lamina....... 45a Submergedleavesobtuseto narrowlyobtuseandslightlyhoodedatapex,9-15-veined;stemunbranched; petiolesof floatingleaves0.1-0.8 timesas long as the lamina;bothsubmergedandfloatingleaves with bundlesabsent............ a strongreddishto brownishtinge, especiallywhendried;interlacunar 13. P alpinus .................................................................. 45b Submergedleaves acute to mucronateand flat at apex, usually 3-11-veined (up to 17-veinedin P illinoensis);stem unbranchedto richlybranched;petiolesof floatingleaves mostly0.8-4.0 timesas bundlespresent long as the lamina;leaves greenor rarelyonly witha slightbrownishtinge;interlacunar or absent.46 orsparinglybranched 46a Submergedleavesdenticulateatmargins;stemusuallyrichlybranched(unbranched in P illinoensis);pedunclesas thick as or up to muchthickerthanthe stem;fruits2.4-3.9 mm long; stele of protoor trio to oblongtype;endodermisof U-type.47 46b Submergedleaves entireat margins;stemunbranchedor sparinglybranched;pedunclesas thickas the stem;fruits 1.7-2.6 mm long; stele of four bundlestype, rarelyof protoor trio type; endodermisof 0-type .48 47a Submergedleaveslinear-oblongto oblongor oblanceolate,mostly5-12 mm wide;stipulesusually6-25 25. P gramineus mm long;fruits2.4-3.1 mm long .......... 47b Submergedleaves narrowlylanceolateor oblongto elliptical,mostly 12-53 mm wide; stipules20-80 mm long;fruits2.7-3.9 mm long.53 to narrowlyelliptical;fruitingspikes 10-25 mm long,6-7 48a Submergedleaves narrowlylinear-lanceolate mm wide; fruits 2.0-2.6 mm long; stipulesusually 25-35 mm long; subepidermalbundlespresent, 33. P cheesemanii mostlystronglydeveloped........... 48b Submergedleavesnarrowlyoblongto broadlyovate;fruitingspikes7-22 mmlong,? 5 mmwide;fruits bundlesabsent....... 32. P drummondii 1.7-2.0(-2.5) mmlong;stipules16-25 mmlong;subepidermal 49a (44) Laminaof submergedleaves sometimessagittateat base, 105-160 mm long; petiolesof floating leaves 115-185 mm long; peduncles considerablythicker than the stem, 130-180 mm long; 18. P papuanicus absent.......... pseudohypodermis 49b Laminaof submergedleaves cuneateto cordateat base, neversagittate,30-310 mm long; petiolesof floatingleaves5-260(-390) mm long;pedunclesas thickas or thickerthanthe stem, 10-350 mm long; 50 absentor mostlypresent........................................... pseudohypodermis 50a Maturesubmergedleaves mucronateat the apex,denticulateat margins(at least in young leaves),near the base of the stem often partlyreducedto phyllodes;petiolesof submergedleaves (0-)2-70(-140) mm long; interlacunar bundlesalwayswell developed;endodermisof U-type,exceptionallyof 0-type 51 .......... ................................................................ 50b Submergedleaveseitherobtuseor acuteat the apex,entireor minutelydenticulateat margins,phyllodes nearthe base of the stem almostalwaysabsent;petiolesof submergedleaves 1-200(-250) mm long; 54 interlacunar bundlespresentor absent;endodermisof 0-type, exceptionallyof U-type ........... 51a Petiolesof submergedleaves 30-70(-140) mm long;submergedleaves oblong,with parallelmargins; fruits2.0-3.3 mm long;pedunclesslightlythickerthanthe stem;stele of triotype, rarelyof prototype 2 1. P wrightii .................................................................. 51b Petiolesof submergedleavesusually(0-)2-40 mmlong;submergedleavesellipticalor lanceolate,with convex margins;fruits 2.7-4.5 mm long; pedunclesdistinctlythickerthan the stem; stele mostly of 52 oblongtype in typicalshoots..................................................... 254 G. Wiegleb & Z. Kaplan 52a Submergedleavesmostlyelliptical,25-65 mmwide,conspicuouslydenticulate;petiolelengthrelatively constant,rangingbetween2-7(-15) mm;floatingleaves alwaysabsent;stele mostlyof oblongtype . . 24. P lucens ....................................... .............................. 52b Submergedleaves narrowlylanceolateto elliptical,mostly5-40 mm wide, often only inconspicuously denticulate;petiole length variable,rangingbetween0-40(-65) nmm long; floatingleaves presentor absent;stele morevariable,rangingfromprototo oblongtype.53 53a Submergedleaves mostly 15-40 mm wide, 9-17-veined, mostly4-6 times as long as wide;laminaof floatingleaves mostly25-65 mm wide ......... 22. P illinoensis ................. 53b Submergedleaves (3-)7-28 mm wide, 7-11-veined, mostly 6-17 times as long as wide; laminaof floatingleaves 12-30 mm wide ....... 23. P schweinfurthii ................. 54a (50) Stem conspicuouslyblack-spotted;submergedleaves undulatealong the margins;interlacunar bundlesabsent........................ 7. P pulcher 54b Stemnot conspicuouslyblack-spotted,sometimesreddish-spotted or mostlywithoutconspicuousspots; submergedleaves ? flat alongthe margins(undulatein P australiensis);interlacunar bundlesabsentor present........................ 55 55a Floatingleaves translucent,membranous,with conspicuoussecondaryveins; fruits 1.3-2.5 mm long; petioles of floatingleaves 5-50 mm long; interlacunar bundlesabsent;subepidermalbundlesalways present;pseudohypodermis 56 present...................... 55b Floatingleaves opaque,coriaceous,with inconspicuoussecondaryveins (in P tepperisecondaryveins conspicuous);fruits 1.8-5.2(-5.7) mm long; petioles of floating leaves 20-260(-390) mm long; interlacunar bundlesabsentormostlypresent;subepidermal bundlespresentorabsent;pseudohypodermis presentor absent........................ 57 56a Fruits1.3-1.9 mm long; laminaof floatingleaves 13-21-veined,2-10 times as long as the petiole; pedunclesnot thickerthanstem ..................... 3. P coloratus 56b Fruits2.0-2.5 mm long; laminaof floatingleaves 9-15-veined, 0.5-5.0 times as long as the petiole; pedunclesthickerthanstem................................4. P australiensis 57a Whole plants strongly reddish brown, especially when dried; submergedleaves decaying early; pseudohypodermis 1. P. ferrugineus alwayspresent................................ 57b Plantspalegreento olive-green,locallyalso witha brownishtinge;submergedleavesdecayingor mostly absentor present.............................. persistent;pseudohypodermis 58 58a Submerged leaves (21-)25-37(-41)-veined, with petioles (2-)6-80 mm long; floating leaves (21-)25-5 1-veined,oftencordateto roundedat base.................................... 59 58b Submergedleaves 3-21-veined, withpetiolesmostly30-250 mm long (in P solomonensisandP fryeri only (1-)5-50 mm long); floatingleaves 9-25-veined (up to 35-veinedin P fryeri), mostlycuneate, sometimesalso roundedto subcordateat base................................ 60 59a Submergedleaves (at least the uppermost)foldedand stronglyarcuate;fruits3.9-5.2(-5.7) mm long, not tricarinate,with an indistinct,smooth dorsal keel only; stem indistinctlysclerenchymatous; pseudohypodermis P. amplifolius present................10. 59b Submergedleaves ? flat; fruits(2.7-)3.0-4.1 mm long, distinctlytricarinate,with stronglysculptured dorsalandlateralkeels;stemstronglysclerenchymatous, withpersistentfibresvisibleto the nakedeye; absent.............................6. pseudohypodermis P sulcatus 60a Unrolledstipules6-15 mm wide,withhyalinemargins,persistent;submergedleavesellipticalto oblong or lanceolate,mostly 1.6-2.8 times as long as wide, obtuse at apex; petioles of submergedleaves (2-)10-35 mm long; laminaof floatingleaves ovate or ellipticalto obovate,1.6-2.8 times as long as wide;petioleof floatingleavesalmostalwayswitha discolouredsectionat thejunctionwiththelamina; pseudohypodermis presentin 2-3(-4) layers.............................. 9. P linguatus 60b Unrolledstipulesmostly3-10 mmwide,withouthyalinemargins,persistenttodecayingearly;submerged leaves lanceolateor ribbon-liketo narrowlyoblongor oblong,mostly2.3-19.0 times as long as wide, acuteto narrowlyobtuseatapex;petiolesof submergedleavesmostly25-250 mmlong(inP solomonensis Taxonomy of Potamogeton 255 and P. fryeri only (1-)5-50 mm long); laminaof floatingleaves narrowlyellipticalto lanceolateor linear-oblong,1.5-6.0 timesas longas wide;petioleof floatingleaveswithormostlywithouta discoloured sectionat thejunctionwiththe lamina;pseudohypodermis absentor presentin 1(-2) layers...... . 61 61a Laminaof submergedleaves lanceolateto ribbon-like,5-8(-15) mmwide, 8-19 timesas long as wide; floatingleaves 9-11-veined; spikesdimorphic,cylindricalor subglobose;stele of reducedtrio or four bundlestype ......................................................... 34. P. solomonensis 61b Lamina of submerged leaves narrowly oblong or oblong to lanceolate, (5-)8-38 mm wide, (1.9-)2.3-11.0(-15.0) times as long as wide; floating leaves 11-35-veined; spikes monomorphic, cylindrical;stele of protoor triotype .. ............................................. 62 62a Petioleof floatinganduppermostsubmergedleaves oftenflattenedandwinged,withundulatemargins; laminaof floatingleaves 21-35-veined;lower submergedleaves sessile to subsessile,the upperones petiolate,the petioles0-40 mm long, 0.0-0.3 timesas long as the lamina;peduncles70-150 mm long; fruits4.5-5.0 mm long;interlacunar bundlespresent....... 8. P.fryeri ........................ 62b Petiole of both floating and submergedleaves terete;lamina of floating leaves 11-25-veined; all submergedleaves (long) petiolate,the petioles (12-)30-250 mm long, (0.2-)0.5-5.0 times as long as the lamina;pedunclesmostly25-120 mm long;fruits1.8-4.8 mm long;interlacunar bundlespresentor mostlyabsent............................................................. 63 63a Fruits2.7-4.8 mm long; submergedleaves (5-)9-21-veined, minutelydenticulateor entireat margins, with petioles30-250 mm long;endodermisof 0-type or U-type ........ ................... 64 63b Fruits1.8-2.6 mm long (up to 3.0 mm long in P tepperi);submergedleaves (3-)5-15-veined, entireat margins,withpetiolesmostly 15-90 mm long;endodermisof 0-type ...... ................. 67 64a Flowerswith 1-2(-3) carpels;petiolesof floatingleaves(50-)80-260(-390) mmlong.. 19.P distinctus 64b Flowerswith (3-)4(-5) carpels;petiolesof floatingleaves 18-210(-280) mm long.65 65a Submergedleavespersistent,(1 -)22-38 mmwide;floatingleavesmostly60-130 mmlong;interlacunar bundlesabsent,rarelya few present;endodermismostlyof 0-type, rarelyof O-U-type... 20. P.nodosus 65b Submergedleaves decayingearly,6-27 mm wide;floatingleavesmostly30-80 mm long;interlacunar bundlespresent;endodermisof U-type,rarelyof 0-type ................................. 66 66a Petiolesof floatingleaves 18-110(-195) mm long, 0.3-3.0 times as long as the lamina;laminamostly 20-41 mm wide; stele of trio type; interlacunar bundlespresentin 2-3 circles;subepidermalbundles present.. 14. P thunbergii 66b Petiolesof floatingleaves usually75-170(-280) mm long, 1.8-6.0 times as long as the lamina;lamina 7-26 mm wide;stele of protoor triotype;interlacunar bundlespresentin 1 circle;subepidermal bundles absentor a few present..............15. P parmatus 67a (63) Submergedleavesdecayingearly,5-9(-1 1)-veined;peduncles0.8-3.0 timesas long as thefruiting spike,slightlythinnerthanthestem;steleof triotype;interlacunar bundlespresent.... 12.P.stenostachys 67b Submergedleaves persistentor decaying,(3-)5-17-veined; peduncles2.5-6.0 times as long as the fruitingspike,as thickas the stem;stele of prototo triotype;interlacunar bundlesabsent.... .... 68 68a Submergedleaves decayingearly,linear-lanceolate to ovate-lanceolate; fruits(2.0-)2.5-3.0 mm long; bundlesabsent...... 5. P. tepperi floatingleaves 15-23-veined;stele of prototo triotype;subepidermal 68b Submergedleaves persistent,linear-oblongto oblong or narrowlyelliptical;fruits 1.8-2.6 mm long; floating leaves mostly 11-19-veined (up to 25-veined in P. polygonifolius);stele of proto type; bundlespresent..................................................... subepidermal 69 69a Submergedleaves5-15 timesas longas wide;fruits1.9-2.6 mm long.............. 69b Submergedleaves 1.9-5.0 timesas longas wide;fruits1.8-2.3 mmlong.2. 1. P.polygonifolius P suboblongus 256 G. Wiegleb & Z. Kaplan AN ACCOUNT OF THE SPECIES 1. Potamogeton polygonifolius POURRET, Mem. Acad. Sci. Toulouse 3: 325. 1788. P natans subsp. polygonifolius (POURR.)HOOK.f., Stud. Fl. Brit. Isl. 370. 1870. P. natans var. y polygonifolius (POURR.)FIORI,Fl. Anal. Ital. 1: 154. 1896. - P. oblongus VIv., Ann. Bot. 1(2): 102. 1804. ("oblongum") - P. affinis BOENN.ex CHAM.et SCHLTDL., Linnaea 2(2): 216. 1827, pro syn. ("affine") -P paludosus BORYex CHAM.et SCHLTDL., Linnaea 2(2): 216. 1827, pro syn. ("paludosum") P microcarpus BOISS.et REUT.,Diagn. P1. Nov. Hisp. 24. 1842. P. polygonifoliussubsp.microcarpus(Boiss. et REUT.)NYMAN, Consp.Fl. Eur.4: 681. 1882. P. polygonifoliusvar.microcarpus(Boiss. et REUT.)A. BENN.,Ann. K. K. Naturhist.Hofmus.Wien7: 287. 1892. - P polygonifolius var.PpseudofluitansSYME,Engl. Bot. ed. 3. 9: 28. 1869. ("pseudo-fluitans") - P polygonifoliussubsp.pseudofluitans(SYME)MAGNIN, Bull. Soc. Bot. France43: 437. 1896. -P cyprifoliusLOWE ex GRAEBN. in ENGL.,Pflanzenr.31 (IV.11): 65. 1907,pro syn. - P scheelei G. PREUSSex GRAEBN.in ENGL.,Pflanzenr. 31 (IV.11): 67. 1907, pro syn. ("Scheelei") = P. anglicus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 180. 1916, pro hybr. P coloratus x P. polygonifolius. Description Rhizomefiliformto slender,terete,perennial,sometimeswithapicalscalyturions.Stemunbranched orspanrngly branched,filiformto slender,terete,annualto perennial,wintergreen,continuingto grow afterflowering; specializeddormantturionsnotdeveloping.Submergedleavesusuallypresent,absentin landformsandshallow waterforms,petiolate;laminalinear-oblongto narrowlyelliptical,50-130(-220) mm long, 3-25(-55) mm wide, 5-15 times as long as wide, yellow-greento brightgreen,often with a reddishtinge, (3-)5-15-veined, withnarrowrowsof lacunaeborderingthe midrib,entireat margins,cuneateat base,narrowlyobtuseat apex; petiole 15-80(-240) mm long, 0.5-5.0 times as long as the lamina.Intermediateleaves sometimespresent, petiolate,oblong.Floatingleaves petiolate;laminaoblongor ellipticalto ovate, (10-)25-75(-105) mm long, (5-)10-65 mm wide, 1.5-4.0 timesas long as wide, opaque,coriaceous,brightgreento brownishgreen,often with a reddishtinge, 11-19(-25)-veined, cuneateto roundedor subcordateat base, acuteto obtuseat apex; petiole(13-)25-150(-300) mm long, 0.5-6.0 timesas long as the lamina.Stipulesaxillary,convolute,10-65 mmlong,translucent, persistent.Peduncles25-100(-185) mmlong,2.5-5.0 timesas longas thefruitingspike, as thick as the stem, insertedin the axils of floatingleaves. Spikes cylindrical,10-42 mm long in fruit, contiguous.Flowersnumerous,with 4 carpels.Fruits1.9-2.6 mm long, dorsalkeel indistinct. Stem anatomy Stele of proto type, endodermismostly of 0-type, sometimes O-U-type, interlacunarbundles absent, subepidermal bundlespresent,pseudohypodermis present,1-2-layered. Distribution W, N, C andS Europe,the Azores,Madeira,N Africa,E NorthAmerica. Hybrids 13 x 1. P.xspathulatusSCHRAD. ex W.D.J.KOCH etZ;z,Cat.PI.Palatinat.5:18.1814, prosp. ("spathulatum") [= P alpinusx P polygonifolius] = P kochii EW. SCHULTZ, Arch. Fl. France Allem. 1: 61 et 72. 1844, nom. illeg. ("Kochii") = P oblongo-rufescens F.W. SCHULTZ, Flora 32(15): 230. 1849, nom. illeg. - P rufescenti-natans F.W. SCHULTZ,Archives de Flore 1(4): 55. 1855, nom. illeg. - P alpino-natansF.W. SCHULTZ,Jahresber. Pollichia20-21: 228. 1863, nom. illeg. P alpinus subsp.spathulatus (SCHRAD.ex W.D.J. KOCHet Zlz) MAGNIN,Bull. Soc. Bot. France 43: 441. 1896. 16 x 1. P. xgessnacensis G. FIsCH.,Mitt.Bayer. Bot. Ges. 1(37):472. 1905. ("Gel3snacensis") [= P natansx P polygonifolius] 25 x 1. P. xianceolatifolius(TISELIUS) C.D. PRESTON, Watsonia 16: 437. 1987. [= P gramineusx P polygonifolius] Taxonomy of Potamogeton 257 P. gramineus f. lanceolatifolius TISELIUS,Potamog. Suec. Exs., fasc. 3: [sched.] no. 139, notulae p. 6. 1897. P gramineus proles heterophyllus var. stagnalis subvar. lanceolatifolius (TISELIUS)GRAEBN.in ENGL., Pflanzenr. 31 (IV.II): 88. 1907. _ P. xseemenii nothof. lanceolatifolius (TISELIUs)HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 231. 1916. ("form") 1 x 48. P. xrivularis GILLOT in MAGNIER, Scrin. Fl. Select. 6: 118. 1887 [= P polygonifolius x P pusillus] P lanceolatus var. rivularis (GILLOT)FRYER,J. Bot. 32: 338. 1894. P lanceolatus subsp. rivularis (GILLOT)MAGNIN,Bull. Soc. Bot. France 43: 441. 1896. = P xmiguelensis DANDY,Bol. Soc. Brot., ser. 2, 44: 5. 1970. Notes (1) P polygonifolius is closely related to P coloratus and P suboblongus. (2) The assumed eastward distribution of P. polygonifolius in Asia can be attributed to confusion with P distinctus. The assumed Southern Hemisphere distribution is due to confusion with southern species like P suboblongus, P cheesemanii, P parmatus, and P stenostachys. The occurrence in these areas has not yet been proved. 2. Potamogeton suboblongus 1916 HAGSTROM,Kungi. Svenska Vetenskapsakad. Handl. 55(5): 182. Description Rhizome slender, terete, perennial, continously growing, turions or winterbuds not seen. Stem unbranched or rarely sparingly branched, slender, terete, perennial, not much differentiated from the horizontal shoot; specialized dormant turions not developing. Differentiation of submerged and floating leaves indistinct. Submerged leaves, if present, petiolate; lamina subcoriaceous, narrowly elliptical to oblong, 30-90 mm long, 8-17(-38) mm wide, 1.9-5.0 times as long as wide, yellow-green to bright green, sometimes with a reddish tinge, 7-15-veined, with narrow rows of lacunae bordering the midrib, entire at margins, cuneate at base, narrowly obtuse at apex; petiole 20-60 mm long, 1.2-1.8 times as long as the lamina. Floating leaves petiolate; lamina oblong to broadly elliptical or ovate, (20-)30-60(-75) mm long, 8-35 mm wide, 1.6-4.0 times as long as wide, opaque, coriaceous, bright green to brownish green, Il-15(-21)-veined, cuneate to truncate or subcordate at base, subacute to rounded at apex; petiole 18-55 mm long, 0.6-1.8 times as long as the lamina. Stipules axillary, convolute, 9-35 mm long, conspicuous, persistent or partly decaying. Peduncles (34-)45-130 mm long, 2.5-4.0(-5.5) times as long as the fruiting spike, as thick as the stem, mostly terminal in the axils of floating leaves. Spikes cylindrical, 10-30 mm long in fruit, contiguous. Flowers numerous, with 4 carpels. Fruits 1.8-2.3 mm long, dorsal keel indistinct. Stem anatomy Stele of proto type, rarely reduced to trio (2) type or complex four bundles type, endodermis of 0-type, interlacunarbundles absent, subepidermal bundles present, in one incomplete ring, pseudohypodermis present, 1-layered. Distribution New Zealand, Tasmania? Note (1) P. suboblongus is a distinct species of the flora of New Zealand. It is closely related to P polygonifolius from the Northern Hemisphere. 3. Potamogeton coloratus HORNEMANN,Fl. Dan. 9(25): 2, tab. 1449. 1813. ("Coloratum") _ P hornemannii G. MEY.,Chloris Han. 521. 1836, nom. illeg. ("Hornemanni") _ P natans var. 6. coloratus (HORNEM.)FIORI,Fl. Anal. Ital. 1: 154. 1896. = P plantagineus DUCROSex ROEM.et SCHULT',Syst. Veg. ed. 16. 3: 504. 1818. - P natans subsp. plantagineus (DUCROSex RotM. et SCHULT.)HOOK.f., Stud. Fl. Brit. Isl. 371. 1870. = P helodes DUMORT.,Fl. Belg. 163. 1827. - P siculus TINEOex Guss., Fl. Sicul. Syn. 2(2): 790. 1845, nom. illeg., non J. PRESL1821. 258 G. Wiegleb & Z. Kaplan = P subflavusH. LORETet BARRANDON,Fl. Montpellier2: 671. 1876. P. alpinus subsp.subflavus(H. LORETet BARRANDON)GRAEBN.in ENGL.,Pflanzenr.31 (IV.11): 74. 1907. -P coloratus f. subflavus (H. LORETet BARRANDON) HAGSTR.,Kungl.SvenskaVetenskapsakad. Handl. 55(5): 179. 1916. Description Rhizomeslender,terete,perennial,overwintering withshortleafy shoots,rarelywithapicalscalyturions.Stem unbranched or very sparinglybranched,terete,annual;specializeddormantturionsnot developing.Submerged leaves petiolate or sometimes subsessile; lamina narrowlyelliptical to oblong, (27-)70-175 mm long, 11-44(-65) mm wide, (2.0-)3.5-8.5 times as long as wide, brightgreen, sometimeswith a reddishtinge, 9-17-veined, with narrowrows of lacunaeborderingthe midrib,entireat margins,cuneateat base, acuteat apex;petiole (3-)15-65 mm long, 0.05-0.40 times as long as the lamina.Floatingleaves presentor rarely absent,shortlypetiolate;laminabroadlyellipticalor broadlyovate to suborbicular,(15-)25-85 mm long, 15-55 mm wide, 1.1-2.0 timesas long as wide,translucent,membranous to subcoriaceous,brightgreen,often with a reddishor brownishtinge, 13-21-veined,truncateto cordateat base, acuteto obtuseat apex;petiole 5-45 mm long, 0.1-0.5 times as long as the lamina.Stipulesaxillary,convolute,20-65 mm long, translucent, persistent.Peduncles(18-)30-180 mm long, 1.3-4.0(-6.1) times as long as the fruitingspike,as thickas the stem.Spikescylindrical,14-45 mm long in fruit,contiguous.Flowersnumerous,with4 carpels.Fruits1.3-1.9 mm long, dorsalkeel indistinct. Stem anatomy Steleof prototype,distinctlylobed,endodernmis mostlyof 0-type, rarelyO-U-type,interlacunar bundlesmostly absent,subepidermal bundlespresent,pseudohypodermis usuallypresent,1-2-layered. Distribution W, C and S Europe,N Africa,SW Asia (Turkey). Hybrids 3 x 25. P. xbillupsiiFRYER, J. Bot. 31: 353, t. 337 et 338. 1893. ("Billupsii") [= P coloratus x P gramineus] 3 x 48. P. xianceolatus SM. in SOWERBY, ENGL.Bot. 28: t. 1985. 1809, pro sp. ("lanceolatum") [= P coloratus x P pusillus] = P lanceolatus var. hibernicus A. BENN.in PRAEGER,Irish Naturalist 5: 243. 1896. - P perpygmaeus HAGSTR.ex DRUCE,Bot. Soc. Exch. Club Brit. Isles 6 (1922): 630. 1923, nom. nud. P xperpygmaeus HAGSTR.ex DRUCE,List Brit. P1. ed 2. 116. 1928. 4. Potamogeton australiensis A. BENNETr, J. Bot. 48: 149. 1910. = ? P. membranaceus HAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5): 157. 1916. Description Rhizomeslender,terete,perennial,turionsor winterbudsnot seen. Stem unbranchedor sparinglybranched, slenderto robust,terete,annual;specializeddormantturionsnot developing.Submergedleaves petiolateto subsessile;laminanarrowlyellipticalto lanceolate,30-50(-90) mm long, 8-24 mm wide, 2-4 timesas long as wide, brightgreen,7-13-veined, with narrowrows of lacunaeborderingthe midrib,entirebut becoming undulateat marginswhen dried,cuneateor truncateat base, subacuteat apex;petiole (2-)10-15(-40) mm long,0.05-0.50 timesas long as the lamina.Floatingleavespresentorabsent,shortlypetiolate;laminabroadly ellipticalto ovate, 15-35 mm long, 12-16 mm wide, 1.2-3.0 timesas long as wide, translucent,membranous, brightgreen,9-15-veined, truncateor subcordateat base,roundedat theapex;petiole10-50 mm long,0.2-1.2 times as long as the lamina.Stipulesaxillary,convolute,15-26 mm long, translucent,persistent.Peduncles 55-95 mm long, 2.5-6.0 times as long as the fruitingspike,usuallythickerthanthe stem,insertedin the axils of submergedor rarely floating leaves. Spikes cylindrical,15-25 mm long in fruit, contiguous.Flowers numerous,with 4 carpels.Fruits2.0-2.5 mm long, dorsalkeel indistinct. Stem anatomy Stele of protoor trio (1) type, lobed, endodermisof 0-type, interlacunar bundlesabsentor scatteredones presentin the outercircle, subepidermalbundlespresent,pseudohypodermis present,1-3-layered. Taxonomy of Potamogeton 259 Distribution Tasmania, SE Australia (exact distribution unknown). Note (1) P australiensis is a distinct species of the flora of Tasmania and Australia. The exact delimitation is still unclear, as confusion with P. cheesemanii, P sulcatus, and P suboblongus has occurred. The present description is based on the authentic specimens collected by Wilson from Merrigang Creek, Victoria, sent by Maiden to A. Bennett and preserved at BM. Only one recent specimen (Morris 258 713, Tasmania, OLD) is included. In their treatment of Potamogeton submitted to Flora of Australia, Papassotiriou, Jacobs and Hellquist include also a form with true floating leaves into their concept of P. australiensis which has not yet been described in the literature.These plants have roundish floating leaves up to 65 mm in length, 55 mm in width and 32 veins. As they also differ in some other characters from the plants known so far (e.g. the larger fruits) they are not included in the present treatment. Cultivation experiments are necessary to test the identity of the divergent morphotypes. 5. Potamogeton tepperi A. BENNETT,J. Bot. 25: 178. 1887. ("Tepperi") - P. tricarinatus F. MUELL.ex A. BENN.,J. Bot. 25: 177. 1887, nom. nud. Description Rhizome slender, terete, perennial, winterbuds not seen. Stem unbranched, slender, terete, annual; winterbuds as axillary leafy shoots, specialized dormant turions not developing. Submerged leaves petiolate, decaying early; lamina linear-lanceolate to ovate-lanceolate, 40-60(-104) mm long, 10-20 mm wide, 2.5-6.0 times as long as wide, pale green, 11-15-veined, with narrow bands of lacunae bordering the midrib, entire at margins, cuneate at base, subacute at apex; petiole 32-65 mm long, 0.5-1.5 times as long as the lamina. Intermediate leaves sometimes present, petiolate. Floating leaves present, petiolate; lamina ovate-lanceolate to ovate, 40-60(-80) mm long, 20-30(-40) mm wide, 1.5-2.5 times as long as wide, coriaceous, bright green, 15-23-veined, with conspicuous secondary veins, subcordate at base, rounded to subacute at apex; petiole 40-80(-100) mm long, 0.8-1.5 times as long as the lamina. Stipules axillary, convolute, 25-40 mm long, decaying early. Peduncle 40-75(-90) mm long, 2.0-6.0 times as long as the fruiting spike, as thick as the stem, inserted in the axils of floating leaves. Spike cylindrical, 15-35 mm long in fruit, contiguous. Flowers 12 to numerous, with 4 carpels. Fruits (2.0-)2.5-3.0 mm long, dorsal and lateralkeels distinct, but not tuberculate. Stem anatomy Stele of proto or trio type, endodermis of 0-type, interlacunarbundles absent, subepidermal bundles usually absent, pseudohypodermis present, 1-layered. Distribution E and SE Australia (exact distribution unknown). Note (1) At present not enough information is available on the exact delimitation of P tepperi. This taxon is not identical with the widespread P sulcatus, as it lacks the tricarinate fruits. It is similar to P suboblongus but differs in the smaller fruit size and the distinct differentiation of submerged and floating leaves. We only recognize the specimens originally collected by Bailey and similar plants collected later along the east cost of Australia. Outside Australia, frequent misapplication of the name P tepperi to P nodosus and P distinctus has occurred, but the taxon is not identical with these species. It is differentiated by the presence of a pseudohypodermis, the absence of dentation of submerged leaves, and the smaller fruit size. Nevertheless P nodosus occurs on the Australian continent. 6. Potamogeton sulcatus A. BENNETT,Ann. K. K. Naturhist. Hofmus. Wien 7: 294. 1892. = P muricatus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 165. 1916. Description Rhizome slender to robust, terete, perennial, winter buds not seen. Stem unbranched, slender to robust, terete, annual; specialized dormant turions not developing. Submerged leaves petiolate; lamina oblong-lanceolate to oblong or elliptical, 50-120(-200) mm long, 10-40(-65) mm wide, 2.2-7.0 times as long as wide, pale green, 27-35 veined, with narrow rows of lacunae bordering the midrib, entire at margins, cuneate to rounded at base, rounded to subacute at apex; petiole (6-)20-80 mm long, 0.1-0.6 times as long as the lamina. Intermediate 260 G. Wiegleb & Z. Kaplan leaves sometimes present, petiolate; petiole up to 140 mm long. Floating leaves present or sometimes absent, petiolate; lamina broadly elliptical to suborbicular, 30-150 mm long, 10-70 mm wide, 1.3-2.7 times as long as wide, opaque, coriaceous, bright green, 25-35(-39)-veined, cordate at base, rounded at apex; petiole 30-60 mm long, 0.5-2.0 times as long as the lamina. Stipules axillary, convolute, 25-40(-50) mm long, translucent, decaying or persistent. Peduncles 40-80(-180) mm long, 0.8-2.3 times as long as the fruiting spike, as thick as or slightly thicker than the stem, inserted in the axils of floating and submerged leaves. Spikes cylidrical, 30-80 mm long in fruit, contiguous. Flowers numerous, with 4 carpels. Fruits (2.7-)3.0-4.1 mm long, dorsal keel distinct, tuberculate, strong lateral keels distinct. Stem anatomy Stele of proto or trio (2) type, with strong sclerenchymatic bundle sheaths and a cambium-like structurebelow the endodermis, endodermis of 0-type, interlacunar bundles present in 1-3 circles, subepidermal bundles present or absent, pseudohypodermis absent. Distribution E and S Australia. Note (1) We choose P sulcatus as the appropriatename of the frequently collected Australian taxon with the fibrous stem. However, the simple equation "P sulcatus = P tricarinatus" does not hold. P sulcatus seems to be restricted to E and S Australia (Murray river catchment). For P tricarinatus see below (under P cheesemanii). 7. Potamogeton puicher TuCKERMAN,Amer. J. Sci. Arts, ser. 1, 45: 38. 1843. = Spirilluspulcher(TUCK.)NIEUWL.,Amer.Midl.Naturalist3: 16. 1913. P pulcher f. amphibius HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 153. 1916. Description Rhizome slender, terete, perennial. Stem unbranched, slender, terete, annual, usually conspicuously black-spotted especially near the base; specialized dormantturions not developing. Submerged leaves petiolate to subsessile; lamina long lanceolate or narrowly oblong to oblong, 80-140(-215) mm long, 10-25(-35) mm wide, 3-10 times as long as wide, yellow-green to bright green, (9-)1 1-21-veined, with narrow rows of lacunae bordering the midrib, entire and usually strongly undulate at margins, narrowly to broadly cuneate at base, acute at apex; petiole 1-15(-18) mm long, 0.0 1-0.20 times as long as the lamina. Intermediateleaves sometimes present. Floating leaves petiolate; lamina broadly oblong or elliptical to broadly ovate, 20-75(-108) mm long, 15-60(-85) mm wide, 1.2-2.5 times as long as wide, opaque, coriaceous, bright green to brownish green, often with a reddish tinge, (19-)21-29(-41)-veined, rounded to subcordate at base, acute to rounded at apex; petiole 36-180 mm long, 0.7-2.5 times as long as the lamina, rarely with a discoloured section at the junction with the lamina. Stipules axillary, convolute, 20-50 mm long, translucent,decaying early to persistent. Peduncles 50-80(-1 10) mm long, 2.0-3.5 times as long as the fruiting spike, as thick as or slightly thinner than the stem. Spikes cylindrical, 20-45 mm long in fruit, contiguous. Flowers numerous, with 4 carpels. Fruits 3.1-4.1(-4.7) mm long, dorsal keel distinct. Stem anatomy Stele of proto type, endodermis of 0-type, interlacunar bundles absent, subepidermal bundles absent, pseudohypodermis present, 1-layered. Distribution C and E North America. 8. Potamogeton fryeri A. BENNETT,J. Bot. 45: 234. 1907. ("Fryeri") = P subsessilifolius A. CAMUSin LEcoMTE,Not. Syst. 1: 86. 1909. - P sessilifolius A. CAMUSin LECOMTE, Not. Syst. 1: 87. 1909, nom. nud. = P torquatus KoIDZ., Bot. Mag. (Tokyo) 43: 397. 1929. Description Rhizome slender to robust, terete, perennial, of aseasonal growth, with wintergreen shoots; winterbuds not developing or as non-dormant scaly turions. Stem unbranched or sparingly branched in autumn, slender to robust, terete, annual or perennial; specialized dormant turions not developing. Submerged leaves usually present, absent in landforms, lower ones sessile to subsessile, the upper ones petiolate; lamina linear-lanceolate Taxonomy of Potamogeton 261 to oblong, sometimesthat of the lowest leaves partlyreducedto phyllodes,105-150 mm long, 12-16 mm wide, 6-11(-14) as long as wide, yellow-greento brightgreen, 5-9-veined, with narrowrows of lacunae borderingthe midrib,entireat margins,cuneateat base, acuteat apex;petiole0-40 mm long, 0.0-0.3 times as long as the lamina,mostly flattenedand winged, with undulatemargins.Intermediateleaves sometimes present,petiolate;petioleup to 115 mm long. Floatingleavesusuallypresent,petiolate;laminalanceolateor oblanceolateto elliptic,65-120(-150) mmlong, 18-40(-75) mmwide, 1.3-5.5 timesas long as wide,opaque, coriaceous,brightgreento olive green,21-35-veined, roundedto broadlycuneateat base andnarrowedinto thepetiole,acuteatapex;petiole(65-)80-2 10mmlong,0.9-2.5 timesas longas thelamina,oftenconspicuously wingedtowardsthe lamina,rarelywitha discolouredsectionat thejunctionwiththe lamina.Stipulesaxillary, convolute,(30-)50-100 cm long, opaque,fibrous,whitish,persistent.Peduncles70-150 mm long, 2-6 times as long as the fruitingspike, as thick as the stem, thinnerdirectlybelow the spike, insertedin the axils of floatingleaves. Spikes cylindrical,20-30(-50) mm long in fruit,contiguous.Flowersnumerous,with (3-)4 carpels.Fruits4.5-5.0 mm long, dorsalkeel distinct. Stem anatomy Stele of proto type, lobed, endodermisof 0-type, interlacunarbundlespresentin 2-3(-4) circles, strong, multicellular,scatteredsubepidermalbundlespresent,pseudohypodermis present,1-2-layered. Distribution EastAsia (Korea,Japan,RussianFarEast,China?). 9. Potamogeton linguatus HAGSTROM in DUSEN,Ofvers. Forh. Kongi. Svenska Vetensk.-Akad. 4: 259. 1901. = ? P montanusC. PRESL,Reliq. Haenk.1(2): 85. 1827. = P. badioviridis HAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5): 161. 1916. Description Rhizomeslenderto robust,terete,perennial,winterbudsnot seen. Stem unbranchedor sparinglybranched, slenderto robust,tereteor subterete,annual;specializeddormantturionsnot developing.Submergedleaves shortpetiolateto subsessile;laminaellipticalto oblongor lanceolate,40-60(-1 10) mm long, (5-)15-34 mm wide, 1.6-2.8(-8.0) as long as wide, yellow-greento brightgreen,13-19-veined,withnarrowrowsof lacunae borderingthe midrib,entire at margins,cuneateat base, obtuse at the apex; petiole (2-)10-35 mm long, (0. 1-)0.2-0.7 timesas long as the lamina.Floatingleavespresentor sometimesabsent,petiolate;laminaovate or ellipticalto obovate,(30-)55-83 mm long, (15-)21-35(-50) mm wide, 1.6-2.5 times as long as wide, opaque,coriaceous,brightgreento olive green, 11-21-veined,cordateto roundedor broadlycuneateat base, acute to roundedat apex; petiole 30-150 mm long, (0.8-)1.7-4.5 times as long as the lamina,sometimes slightlywingedtowardsthe lamina,almostalwayswith a discolouredsectionat thejunctionwith the lamina. Stipulesaxillary,convolute,40-60(-80) mm long, unrolledup to 15 mm wide, translucent,with hyaline margins,persistent.Peduncles45-80(-200) mm long, 2-5 timesas long as the fruitingspike,as thickas the stem, insertedin the axils of floatingand submergedleaves, rarelysuboppositeto submergedleaves. Spikes cylindrical,15-40 mm long in fruit,contiguous.Flowersnumerous,with 4 carpels.Fruits(3.5-)3.7-4.5 mm long, rugosewhen dried,dorsalkeel indistinct. Stem anatomy Steleof prototype,lobed,endodermisof 0-type, interlacunar bundlespresentin 1 circleorabsent,subepidermal bundlespresentin 1 incompletering,pseudohypodermis present,2-3(-4) layered. Distribution SouthAmericasouthof 380 S (Argentine,Chile,FalklandIslands). Note (1) The morphologicalvariationand distributionof P linguatusis insufficientlyknown. Nevertheless,we assumethatit formsa naturalgroupwith P fiyeri andP. amplifolius. 10. Potamogeton amplifolius TUCKERMAN, Amer. J. Sci. Arts, ser. 2, 6: 225. 1848. Spirillusamplifolius(TUCK.)NIEUWL., Amer.Midl.Naturalist3: 16. 1913. = P subobtususHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 147. 1916, pro hybr.P alpinusx P nodosus. 262 G. Wiegleb & Z. Kaplan = P amplifoliusf. homophyllusHAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5): 163. 1916. = ? P.scoliophyllusHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 164. 1916,prohybr.P amplifolius x P. illinoensis. Description Rhizomeslenderto robust,terete,perennial.Stemunbranched or sparinglybranched,slenderto robust,terete, annualto perennial,overwinteringas shortenedshoots;specializeddormantturionsnotdeveloping.Submerged leaves petiolateto subsessile;laminalanceolateto ovate or broadlyelliptical,folded and stronglyarcuate, 80-170(-210) mm long, 25-75 mm wide, (1.3-)2.0-3.8(-5.4) times as long as wide, bright green or yellow-greento darkgreen,sometimeswitha brownishtinge,(21-)25-37(-4 1)-veined,withoutrowsof lacunae borderingthe midrib,entireat margins,narrowlyto broadlycuneateat base, obtuseto acuteat apex;petiole (2-)6-60 mm long, 0.02-0.30 times as long as the lamina.Intermediateleaves sometimespresent.Floating leavespetiolate;laminabroadlyoblongor ellipticalto ovate,45-105 mmlong,22-50 mm wide, 1.8-2.9 times as long as wide, opaque, coriaceous, bright green to olive green, sometimes with a reddish tinge, (21-)29-41(-51)-veined, cuneateto roundedor subcordateat base, acuteto roundedor mucronateat apex; petiole(45-)80-200 mm long, (0.7-)1.1-2.3 times as long as the lamina,rarelywith a discolouredsectionat thejunctionwiththe lamina.Stipulesaxillary,convolute,35-1 l0(-185) mm long,translucent,decayingearly to persistent.Peduncles50-85(-1 10) mm long, 1.0-2.5(-4.0) times as long as the fruitingspike,as thickas or thickerthanthestem.Spikescylindrical,25-50 mmlong in fruit,contiguous.Flowersnumerous,with(2-)4 carpels.Fruits3.9-5.2(-5.7) mm long, dorsalkeel indistinct. Stem anatomy Stele of prototype, lobed, endodermisof 0-type, interlacunar bundlespresent,multicellular,subepidermal bundlesabsent,pseudohypodermis present,1(-2)-layered. Distribution W, C andE NorthAmerica. 11. Potamogeton ferrugineus HAGSTROM, Kungl. Svenska Vetenskapsakad. Handl. 55(5): 161. 1916. P. apicalis HAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 156. 1916. = ? P. spoliatusHAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5): 168. 1916. - Description Rhizomeslenderto robust,terete,perennial,winterbudsnot seen. Stemunbranched,slenderto robust,terete, annual,dark-spottednearthe base; specializeddormantturionsnot developing.Submergedleaves petiolate; laminabroadlylanceolate,decayingearly,(80-)150-240 mm long, (18-)25-40 mm wide, 1.8-6.5 times as long as wide,green,with a reddishor brownishtinge,especiallywhendried,13-23-veined,withnarrowrows of lacunaeborderingthe midrib,entireat margins,cuneateat base, acute at apex;petiole (10-)40-140 mm long, 0.05-0.45 times as long as the lamina.Floatingleaves petiolate;laminabroadlylanceolateto ovate or elliptical,50-85(-120 mm) long, 15-38 mm wide, 1.8-3.5 times as long as wide, green, with a reddishor brownishtinge, stronglyreddishbrownwhen dried, 15-23-veined,cuneateat base, obtuseto acuteat apex; petiole40-80(-140) mm long, 0.8-1.5 times as long as the lamina.Stipulesaxillary,convolute,35-65 mm long,translucent, persistent,2-keeled at base.Peduncles40-90 mmlong, 1.5-4.1 timesas long as thefruiting spike,as thickas or slightlythickerthanthe stem.Spikescylindrical,17-40(-60) mmlong in fruit,contiguous. Flowersnumerous,with 4 carpels.Fruits3.5-4.5(-5.0) mm long, dorsalkeel distinct. Stem anatomy Stele of protoor trio(2) type,endodermisof 0-type, rarelyfaintU-type,interlacunar bundlesabsentor 1 circle present,scatteredsubepidermalbundlespresentor absent,pseudohypodermis present,(l-)2(-3) layered. Distribution SouthAmerica(Argentina,Uruguay,Brazil). Note (1) The descriptionof P.ferrugineushasuntilrecentlybeenobscuredby confusionwithP illinoensis.Despite ourinvestigationssomeuncertaintieswithrespectto distribution andtaxonomicrelationof the speciesremain. In particular, plantsdescribedas P. spoliatusshow some deviatingcharacters. Taxonomy of Potamogeton 263 12. Potamogeton stenostachys K. SCHUMANN in MARTIUS, Fl. Bras. 3(3): 687, t. 119, fig. 1. 1894. Description Rhizomeslenderto robust,terete,perennial,winterbudsnot seen. Stem unbranched,slender,terete,annual; specializeddormantturionsnot developing.Submergedleaves petiolate;laminalanceolate,decayingearly, 60-105 mmlong, 12-20 mmwide, 3.0-7.5 timesas longas wide,brightgreento darkgreen,5-9(-l 1)-veined, with narrowrows of lacunaeborderingthe midrib,entireat margins,cuneateat base, acuteat apex;petiole 65-90 mmlong,0.7-1.5 timesas longas thelamina.Floatingleavespetiolate;laminaellipticalto ovate,30-90 mmlong, 13-35 mmwide, 1.7-3.0 timesas long as wide,brightgreen,oftenwitha brownishor reddishtinge, 15-23-veined,cuneateto roundedat base, obtuseto subacuteat apex;petiole27-65(-120) mm long, 0.7-4.0 timesas longas thelamina.Stipulesaxillary,convolute,30-72 mmlong,opaque,persistent,whitish.Peduncles 25-140 mm long,0.8-3.0 timesas long as the fruitingspike,slightlythinnerthanthe stem.Spikescylindrical, 25-45 mm long in fruit,contiguous.Flowersnumerous,with 4 carpels.Fruits1.8-2.5, dorsalkeel indistinct. Stem anatomy Stele of trio type (2), endodermisof 0-type, interlacunar bundlespresentin 2 circles, subepidermal bundles absent,pseudohypodermis present,1-2-layered. Distribution SouthAmerica(Brazil). Note (1) P. stenostachysis insufficientlyknown,even thoughit is clearlydistinctfromotherSouthAmericantaxa. The presentdescriptionis basedon the type specimenRiedel834 andthe herbarium collectionsUle 1308 and Ule 6942. 13. Potamogetonalpinus BALBIS,Mem. Acad. Sci. Turin, Sci. Phys. Math. 1, 10-11 (1802-1803): 329. 1804. ("alpinum") P lucens var.P.alpinus (BALB.)FIORI,Fl. Anal. Ital. 1: 154. 1896. ("alpina") = P. annulatus BELLARDI,Mem. Acad. Sci. Turin, Sci. Phys. Math. 1, 10-11 (1802-1803): 447, t. 1, fig. 2. 1804. = P tenuifoliusRAF.,Med. Repos.,Hexade3, 2: 409. 1811. ("tenuifolium") P alpinus subsp. tenuifolius (RAF.) HULTEN,Fl. Aleut. IsI. 65. 1937. = P semipellucidusW.D.J.KOCHet Zlz, Cat.P1.Palatinat.5: 18. 1814. ("semipellucidum") = P rufescens SCHRAD.ex CHAM.,Adnot. Fl. Berol. 5. 1815. = P obscurusDC. in LAM.et DC., Fl. Fran. ed. 3, 6: 311. 1815.("obscurum") = P purpurascens SEIDLex J. PRESLet C. PRESL,Fl. Cech. 37. 1819. = P. microstachys WOLFG.in SCHULT.et SCHULT. f., Mant. 3: 360. 1827. = P obrutus A.W.WOOD,Class-book Bot. 176. 1845. = P casparyi KOHTS,Oesterr. Bot. Z. 20: 289. 1870. ("Casparyi") P alpinus proles casparyi (KOHTS)GRAEBN.in ENGL., Pflanzenr. 31 (IV.11): 74. 1907. ("Casparyi") - P thomasiiA. BENN.,Ann. K. K. Naturhist.Hofmus.Wien7: 288. 1892,pro syn. ("Thomasii") P stylatus HAGSTR., Bot. Not. 1908: 98. 1908. - - P montanensisGAND.,Bull. Soc. Bot. France66: 304. 1919. ("montanense") P palmeriiDRUCE, List Brit.P1.ed 2. 116. 1928,nom. nud.("Palmeri") Description Rhizome slender, terete, perennial,with scaly apical turions.Stem unbranched,slender,terete, annual; specializeddormantturionsnotdeveloping.Submergedleavespresent,absentin landforms,sessile,lanceolate to oblong, (51-)70-180(-380) mm long, (7-)10-25(-33) mm wide, 4-10(-14) times as long as wide, yellow-greento brightgreen,often with a reddishtinge,especiallystrongwhendried,(7-)9-15-veined, with broadrowsof lacunaeborderingthe midrib,entireat margins,cuneateat base, obtuseto narrowlyobtuseand slightlyhoodedat apex. Intermediateleaves sometimespresent.Floatingleaves presentor absent,petiolate; laminaoblongor oblanceolateto obovate,(24-)42-90 mimlong, 8-25 mm wide, 2-6 timesas long as wide, opaque,subcoriaceousto coriaceous,yellow-grcen,usuallywitha reddishor brownishtinge,especiallywhen dried,9-19-veined,cuneateto attenuateat base,obtuseat apex;petiole 10-35 mm long,0.1-0.8 timesas long as the lamina.Stipulesaxillary,convolute,(12-)18-35(-50) mm long, translucent,decayingearly.Peduncles 264 G. Wiegleb & Z. Kaplan 30-150(-310) mm long, 2-5(-9) times as long as the fruitingspike,as thickas the stem. Spikescylindrical, 15-40 mm long in fruit,contiguous.Flowersnumerous,with 4 carpels.Fruits2.6-3.7 mm long, dorsalkeel distinct. Stem anatomy Stele of trio (2) type, endodermisof 0-type, interlacunarbundles absent, subepidermalbundles absent, pseudohypodermis absent,rarely1-layered. Distribution Circumboreal, throughoutthe NorthernHemisphere. Hybrids 13 x 1. P.xspathulatusSCHRAD.exW.D.J. KOCH etZiz, Cat. Pi. Palatinat. 5:18.1814, pro sp. ("spathulatum") [= P. alpinusx P. polygonifolius] 13 x 24. P. xnervigerWOLFG.in SCHULT. et SCHULT. f., Mant.3: 359. 1827, pro sp. [= P alpinusx P. lucens] P rufescensvar.b) nerviger(WOLFG.) K. RICHT.,PI.Eur.1: 12. 1890. P alpinusvar.purpurascenssubvar.nerviger(WOLFG.)ASCH.et GRAEBN.,Synops.Mitteleur.Fl. 1: 311. 1897. _ P alpinusvar.nerviger(WOLFG.) G. FIsCH.,Mitt.Bayer.Bot. Ges. 4(10): 153. 1930. - P nervigerusWOLFG., Herb.Eichw.Skizze 125. 1830. [nonvidimus] 13 x 25. P. xnericius HAGSTR., Kungi. Svenska Vetenskapsakad. Handl. 55(5): 145. 1916. [= P alpinusx P gramineus] 13 x 26. P. xprussicus HAGSTR.,Bot. Not. 1908: 103.1908. [= P alpinusx P perfoliatus] P johannis HESL.-HARR.,Occas. Notes Dept. Bot., King's Coll., Newcastle upon Tyne 2: 3. 1941. 13 x 28. P. xgriffithiiA. BENN.,J. Bot. 21: 65, t. 235. 1883. ("Griffithii") [= P alpinus x P praelongus] - P macvicarii A. BENN., Ann. Scott. Nat. Hist. 62: 106. 1907. ("Macvicarii") 13 x 35. P. xolivaceus BAAGOEex G. FISCH.,Ber. Bayer. Bot. Ges. 11: 33. 1907. [= P alpinus x P crispus] - P xvenustus BAAGOE,Actes 1. Congr. Intern. Bot. Paris 516. 1900, nom. nud. = P xvenustus BAAGOEex A. BENN.,J. Bot. 45: 375. 1907. - ? P. baagoei A. BENN. [apud GRAEBN.]in ENGL.,Pflanzenr. 31 (IV.11): 132. 1907, nom. nud. ("Baagoei") = P xvenustus BAAGOEex HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 144. 1916, nom. illeg. - Note (1) P alpinus might be sometimes confused with other similar plants. However, it is a taxonomically well defined species. It shows an extreme regional and ecological polymorphism. 14. Potamogeton thunbergii CHAMISSO et SCHLECHTENDAL, Linnaea 2(2): 221, t. 6, f. 21. 1827. ("Thunbergii") P americanus var. thunbergii (CHAM. et SCHLTDL.)A. BENN. in DYER, Fl. Capens. 7: 46. 1897. ("Thunbergii") P fluitans proles thunbergii (CHAM.et SCHLTDL.) GRAEBN.in ENGL.,Pflanzenr. 31 (IV.11): 61. 1907. = P natans var. angustatus b) capensis CHAM.ex KUNTH,Enum. P1. 3: 128. 1841. = P richardii SOLMSin SCHWEINF., Beitr. FH.Aethiop. 194. 1867. ("Richardi") P americanus var. richardii (SOLMS)SOLMSex SCHWEINF.,Bull. Herb. Boissier 2, App. 2: 8. 1894. ("Richardi") = P natans var. capensis T. DURANDet SCHINZ,Consp. Fl. Afric. 5: 494. 1894. = P fibrosus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 160. 1916. Description Rhizome slender to robust, terete, perennial, with apical scaly turions. Stem unbranched, slender, terete, annual; specialized dormant turions not developing. Submerged leaves petiolate; lamina lanceolate to oblong, decaying early, sometimes the lower ones reduced to phyllodes, 80-200 mm long, 5-27 mm wide, 5-13 times as long Taxonomy of Potamogeton 265 as wide, brightgreento darkgreen,9-17-veined, withnarrowrows of lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base, acuteat apex;petiole(10-)45-180 mm long, 0.2-1.8 times as long as the lamina. Intermediateleaves often present. Floating leaves petiolate;lamina elliptical to oblong-ovate, 30-80(-124) mm long, (11-)20-40(-48) mm wide, 1.6-3.5(-5.0) timesas long as wide, opaque,coriaceous, olive greento darkgreen, 11-25-veined,broadlycuneateto roundedat base, broadlyacute at apex;petiole 18-110(-195) mm long, (0.3-)0.6-3.0 times as long as the lamina,almostalwayswith a discolouredsection at the junctionwith the lamina.Stipulesaxillary,convolute,25-40(-60) mm long, translucent,persistentto decayingearly.Peduncles50-100 mm long, 2.0-3.5 times as long as the fruitingspike,as thickas the stem, insertedintheaxilsof floatingleaves.Spikescylindrical,30-50 mmlongin fruit,contiguous.Flowersnumerous, with 4 carpels.Fruits3.2-4.8 mm long, dorsalkeel distinct. Stem anatomy Stele of trio(2) type, endodermisof U-type,interlacunar bundlespresentin 2-3 circles,subepidemalbundles present,pseudohypodermis present,1-layered. Distribution Africa(in particularSouthandEast Africa),Madagascar, MascareneIslands? Notes (1) P thunbergiiis superficiallymorphologically similarto P nodosus.However,accordingto its stemanatomy and some morphologicalcharacterslike the presenceof phyllodialleaves andthe discolouredjoint at the top of the petiole,it is moreclosely relatedto P natans. (2) Theexactidentityof P xbunyonyiensis DENNY et LYE,Kew Bull.28(1): 120. 1973,introducedas a hybrid P schweinfurthii x P thunbergii,is stillunderconsideration andcannotbe listedwithcertaintyamongconfirmed hybrids. 15. Potamogeton parmatus HAGSTROM, Bot. Not. 1908: 97. 1908. Description Rhizomeslender,terete,perennial,winterbudsnot seen. Stemunbranched, slender,terete,annual;specialized dormantturionsnotdeveloping.Submergedleavespetiolate;laminalanceolateto oblong,decayingearly,40-75 mm long, 6-16(-23) mm wide, 2.3-3.8 timesas long as wide, green,(5-)7-13-veined, with narrowrowsof lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base, acuteat apex;petiole70-195 mm long, 1.6-3.3 timesas long as the lamina.Floatingleavespetiolate;laminaoblongor oblanceolateto obovate, 45-63 mmlong,7-26 mm wide, 2.1-4.2 timesas long as wide,opaque,coriaceous,olive greento darkgreen, sometimes with a brownish tinge, (9-)11-19-veined, broadly cuneate at base, acute at apex; petiole 75-170(-280) mm long, 1.8-6.0 times as long as the lamina.Stipulesaxillary,convolute,30-45 mm long, translucent,decayingearly.Peduncles50-120 mm long, 2-6 timesas long as the floweringspike,as thickas the stem, insertedin the axils of floatingleaves. Spikes cylindrical,14-20 mm long in flower,contiguous. Flowersnumerous,with 4 carpels.Fruitsnot seen. Stem anatomy Stele of protoor trio (2) type, endodermisof U-type,interlacunar bundlespresentin 1 circle, subepidermal bundlesabsentor a few present,pseudohypodermis absentor 1-layered. Distribution Madagascar, E Africa? Note (1) P parmatushasbeenrecordedonly froma restrictedgeographicalarea.It hasneverbeenre-collectedsince its firstformaldescription(HAGSTROM 1908).Becauseof theuniquecharactercombination,however,we are inclinedto maintainit as a separatespecies,beingclosely relatedto bothP thunbergiiandP schweinfurthii. It may proveto be a hybridor an extrememorphotypeof one of these species(cf. P xbunyonyiensis, DENNY & LYE 1983). 16. Potamogeton natans Linnaeus, Sp. PI. 126. 1753. -P Spirillus natans (L.) NIEUWL.,Amer. Midl. Naturalist 3: 16. 1913. natans [subsp.] a. vulgaris SCHUBL.et G. MARTENS,Fl. Wurttemb. 109. 1834, nom. inval. 266 G. Wiegleb & Z. Kaplan - P natans [subsp.] a) vulgaris CELAK.,Analyt. Kvet. Cech, Mor. a Rak. Slezska ed. 3. 45. 1897, nom. inval. - P. serotinus SCHRAD.ex SCHULT.et SCHULT. f., Mant. 3: 351. 1827, pro syn. ("serotinum") = P. natans var. P. ovalifolius FIEBER in BERCHT.et FIEBER,Potam. Bohmens 23. 1838; FIEBERin BERCHT et OPIZ,Oekon.-Techn. Fl. Bohm. 2(1): 260. 1838. -P paludosus BOENN.ex STEUD.,Nomencl. Bot. ed. 2. 2: 384. 1841, pro syn. = P natans var. P. prolixus W.D.J. KOCH,Syn. Fl. Germ. Helv. ed. 2. 775. 1844. = P natans var. b. angustifolius G. MEY.,Fl. Hanov. Exscurs. 537. 1849, nom. illeg. = P morongii A. BENN.,J. Bot. 39: 145. 1902. ("Morongii") = ? P floridanus SMALL,Fl. Southeast. Unit. St. 37. 1903. = P gessnacensis var. richtsfeldii f. hibernicus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 192. 1916. P hibernicus (HAGSTR.)DRUCE,List Brit. P1. ed 2. 116. 1928. Description Rhizome slender to robust, rarely filiform, terete, perennial, overwintering with phyllodial shoots. Stem unbranched or sparingly to richly branched, slender to robust, terete, annual to perennial, wintergreen, dark-spottednear the base; winterbudsas axillary, short, leafy shoots, specialized dormantturionsnot developing. Submerged leaves sessile; lamina reduced to linear phyllodes, 100-450(-610) mm long, 0.8-3.5 mm wide, 70-200(-300) times as long as wide, dark green, 1-3-veined, lateral veins inconspicuous, entire at margins, straight at base, narrowly obtuse to acuminate at apex. Intermediateleaves rarely present, narrowly lanceolate, long petiolate. Floating leaves petiolate; lamina oblong to broadly elliptical or broadly ovate, 40-100(-140) mm long, (7-)20-45(-80) mm wide, 1.5-3.5(-5.2) times as long as wide, opaque, coriaceous, brown-green or yellow-green to olive green or dark green, sometimes with a brownish tinge, 17-31(-35)-veined, cuneate to rounded or subcordate at base, acute to obtuse at apex; petiole 50-150(-300) mm long, 0.7-5.0 times as long as the lamina, almost always with a discoloured section at the junction with the lamina. Stipules axillary, convolute, 40-170 mm long, translucent, persistent. Peduncles 35-90(-125) mm long, 1.2-3.0 times as long as the fruiting spike, as thick as the stem. Spikes cylindrical, 20-60 mm long in fruit, contiguous. Flowers numerous, with 4 carpels. Fruits 3.8-5.0 mm long, dorsal keel indistinct to distinct. Stem anatomy Stele of eight bundles or complex oblong type, endodermis of U-type, interlacunar bundles present in 3-4 circles, multicellular, subepidermal bundles present, pseudohypodermis present, 1-2-layered. Distribution Circumpolar, boreal and temperate regions of the Northern Hemisphere. Hybrids 16 x 1. P xgessnacensis G. FISCH.,Mitt. Bayer. Bot. Ges. 1(37): 472. 1905. ("GeBsnacensis") [= P natans x P polygonifolius] 16 x 20. P xschreberi G. FISCH.,Mitt. Bayer. Bot. Ges. 1(37): 471. 1905. ("Schreberi") [= P natans x P. nodosus] 24 x 16. P xfluitans ROTH,Tent. Fl. Germ. 1: 72. 1788, pro sp. [= P lucens x P natans] -P natans [var.] P.fluitans (ROTH)CHAM.,Adnot. Fl. Berol. 4. 1815. -P natans [subsp.] y. fluitans (ROTH)SCHUBL.et G. MARTENS,Fl. Wurttemb. 109. 1834. = P oblongus [var.] ("spielart")a. fluitans (ROTH)G. MEY.,Chlon's Han. 520. 1836. - P rothii A. BENN.ex G. FISCH.,Mitt. Bayer. Bot. Ges. 1(31): 362. 1904, nom. inval. ("Rothii") - P xcrassifolius FRYER,J. Bot. 28: 321, t. 299. 1890. - P xolivaceus BAAGOE,Actes 1. Congr. Intern. Bot. Paris 516. 1900, nom. nud. P xnoltei G. FISCH.,Mitt. Bayer. Bot. Ges. 37: 472. 1905, nom. illeg. ("Noltei"), non A. BENN. 1890. - P noltei ser. harzii G. FISCH.,Ber. Bayer. Bot. Ges. 11: 57 et 145. 1907, nom. inval. ("Harzii") - P noltei var. P. harzii G. FISCH.ex GRAEBN.in ENGL.,Pflanzenr. 31 (IV. 1I):137. 1907, nom. inval. ("Harzii") = P harzii G. FISCH.,Mitt. Bayer. Bot. Ges. 3(5): 104. 1914. ("Harzii") = P fluitans proles raunkiaeri G. FISCH.,Mitt. Bayer. Bot. Ges. 3(5): 103. 1914. ("Raunkiaeri") - P fluitans ser. raunkiaeri (G. FISCH.)G. FISCH.,Mitt. Bayer. Bot. Ges. 4(10): 154. 1930, nom. inval. Taxonomy of Potamogeton 267 = P. xsterilis HAGSTR., Kungl. Svenska Vetenskapsakad. Handl. 55(5): 238. 1916. = P xsubrufus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 241. 1916. 25 x 16. P. xsparganiifolius LAEST.ex FR., Novit. Fl. Suec. Mant. 1: 9. 1832. ("sparganifolius") [= P. gramineus x P natans] -P natans proles sparganiifolius (LAEST.ex FR.) AsCH. et GRAEBN.,Synops. Mitteleur. Fl. 1: 304. 1897. -P. natans subsp. sparganiifolius (LAEST.ex FR.) SCHINZet THELL.,Fl. Schweiz ed. 3. 2: 15. 1914. = P. natans subsp. kirkii SYMEex HOOK.f., Stud. Fl. Brit. IsI. 371. 1870. ("Kirkii") - P kirkii SYME,ENGL.Bot. ed. 3. 9: 31. 1869, pro syn. ("Kirkii") P kirkii (SYMEex HOOKf.) SYMEex HOOKf., Stud. Fl. Br. Isl. ed. 3. 435. 1884. P xtiselii K. RICHT.,P1. Eur. 1: 13. 1890. ("Tiselii") = P dubius TISELIUS,Potamog. Suec. Exs., fasc. 1: [sched.] no. 19, notulae p. 5. 1894. 25 x 48. P xvariifolius THORE,Essai Chloris 47. 1803, pro sp. ("variifolius") [= P. natans x P pusillus] P gramineus subsp. variifolius (THORE)NYMAN,Consp. Fl. Eur. 4: 682. 1882. -P javanicus subsp. variifolius (THORE)P. FOURNIER, Quatre Fl. Fr. 140. 1935. 25 x 56. P. xyamagataensis KADONO et WIEGLEB, J. Jap. Bot. 62(3): 73. 1987. [= P natans x P octandrus] - P pleiophyllus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 159. 1916, p. p. ? 25 x 68. P. xnomotoensis KADONO et T. NOGUCHI, Acta Phytotax. Geobot. 42(2): 175. 1991, pro sp. [= ? P natans x P pectinatus] Notes (1) P floridanus is a unique plant collected from a restricted area. Morphologically it is similar to a juvenile P. natans. It differs from the type in its completely different shoot anatomy. Anatomical characters point to hybridization with P illinoensis or P gramineus. Both its identity with P natans or a hybrid of this species have been rejected in the past for phytogeographical reasons. (2) The authenticcollection of P pleiophyllus includes both P xyamagataensis and P nodosus. Furtherspecimens are listed in its protologue including also P distinctus and maybe even P natans. A lectotype specimen has to be selected in the future to elucidate the identity with P. xyamagataensis. (3) P xnomotoensis displays a unique charactercombination of a broad-leaved species with long adnate stipules. It could represent a hybrid, a hybridogenous species or an extreme deviation of a broad-leaved species like P. natans (for an analogous case of the last possibility see HELLQUIST 1978). Further research is necessary. (4) The name "P fluitans" has been misapplied to almost all broad-leaved species with floating leaves. Most of specimens named as such relate to P nodosus, but by no means all records of "P fluitans" can be explained in this way. Despite the lack of type specimens we adopt the name for the hybrid P. natans x P lucens, being aware of the fact that this hybrid still grows not far from the type locality in the same river. 17. Potamogeton oakesianus J.W. ROBBINSin GRAY,Manual Bot. North. U. S. ed. 5. 485. 1867. ("Oakesianus") Description Rhizome slender, terete, perennial. Stem unbranchedor sparingly branched, slender, terete, annual to perennial, overwintering as shortened shoots; specialized dormant turions not developing. Submerged leaves sessile; lamina reduced to linear phyllodes, 50-160 mm long, (0.2-)0.3-1.0 mm wide, 120-300 times as long as wide, dark green, 1-3-veined, lateral veins inconspicuous, entire at margins, straight at base, narrowly obtuse to acuminate at apex. Floating leaves petiolate; lamina oblong to elliptical or broadly ovate, (13-)22-40(-55) mm long, (5-)10-22(-29) mm wide, 1.5-2.7 times as long as wide, opaque, coriaceous, bright green to olive green, sometimes with a brownish tinge, (7-)9-19(-23)-veined, cuneate to rounded at base, broadly acute to obtuse at apex; petiole 25-70(-100) mm long, 1.0-2.5 times as long as the lamina, often with a discoloured section at the junction with the lamina. Stipules axillary, convolute, 10-40(-55) mm long, translucent,persistent. Peduncles 25-60 mm long, 1.5-2.5 times as long as the fruiting spike, usually thicker than the stem. Spikes cylindrical, 15-30 mm long in fruit, contiguous. Flowers numerous, with 4 carpels. Fruits 2.5-3.5(-3.7) mm long, dorsal keel distinct. 268 G. Wiegleb & Z. Kaplan Stem anatomy Stele of trio type, endodermisof U-type, interlacunar bundlesin 1-2 circles present,subepidermalbundles present,pseudohypodermis absentor present,1-layered. Distribution C andE NorthAmerica. Note (1) P. oakesianusis closely relatedto P natans.It comprisesmorphotypeswith a special characterpattern distributedwithina limitedgeographicalarea. 18. Potamogeton papuanicus WIEGLEB, Blumea 37: 379. 1993. Description Rhizomeslender,terete,perennial.Stem unbranchedor very sparinglybranched,slender,terete,annualor perennial,continuinggrowthafterflowering;specializeddormantturionsnot developing.Submergedleaves petiolateor sometimessubsessile;laminanarrowlyoblong to oblong-lanceolate,105-160 mm long, 12-30 mm wide,4-9 times as long as wide, brightgreen,sometimeswitha reddishtinge,7-13-veined, withnarrow rows of lacunaeborderingthe midrib,entireat margins,cuneateto slightlycordateor sagittateat base,acute at apex; petiole 5-45 mm long, 0.1-0.5 times as long as the lamina. Floating leaves petiolate;lamina oblong-lanceolateto elliptical,65-115 mm long, 18-30 mm wide, 2-5 times as long as wide, translucent, membranous to subcoriaceous,brightgreen,sometimeswitha reddishorbrownishtinge,9-15-veined,cuneate atbase,acuteatapex;petiole115-185 mmlong,0.5-3.0 timesas longas thelamina.Stipulesaxillary,convolute, 20-60 mmlong,translucent, persistent.Peduncles130-180 mmlong, 5-7 timesas long as thefloweringspike, thickerthanthe stem, insertedin the axils of floatingand submergedleaves. Spikes cylindrical,21-28 mm long in flower,contiguous.Flowersnumerous,with 4 carpels.Fruitsnot seen. Stem anatomy Steleof protoor trio(2) type,endodermisof 0-type, interlacunar bundlesabsent,subepidermal bundlesabsent, pseudohypodermis absent. Distribution Papua-NewGuinea,LesserSundaIsles? Note (1) Bothmorphologyanddistributionof P papuanicusarestill insufficientlyknown.The speciesis relatedto P distinctusandP. nodosus. 19. Potamogeton distinctus A. BENNETT, J. Bot. 42: 72. 1904. P digynusWALLICH, Numer.List 181, no. 5177. 1832, nom.nud. = P natansf. indicusMIQ.,Fl. Ind. Batav.,Suppl. 1 [= Fl. Ned. Ind., EersteBijv.], 2: 259, 3: 597. 1861. ("indica") = P malaianusvar.tenuiorMIQ.,Ill. Fl. ArchipelInd. 1: 47. 1870. = P.franchetiiA. BENN.et BAAGOE ex A. BENN.,J. Bot. 45: 234. 1907. ("Franchetii") = P tepperivar.a. attenuatusA. CAMUS in LECOMTE, Not. Syst. 1: 85. 1909. = P tepperivar.P. subcordatusA. CAMUS in LECOMTE, Not. Syst. 1: 85. 1909. = P longipetiolatusA. CAMUS in LECOMTE, Not. Syst. 1: 88. 1909. = P. perversusA. BENN.,Philipp.J. Sci. 9: 343. 1914. = P. alatus KoIDZ.,Bot. Mag. (Tokyo)43: 397. 1929. = P fontigenusY.H.Guo, X.Z. SUNet H.Q.WANG,Bull. Bot. Res. North.-East.Forest.Inst.5(2): 133. 1985; Y.H.Guo, H.Q. WANGet X.Z. SUN,Acta Bot. Bor.-Occid.Sin. 5(4): 301. 1985. - Description Rhizomeslender,terete,perennial,with apicalwinterbuds.Stemunbranched or sparinglybranched,slender, terete,annual;specializeddormantturionsnotdeveloping.Submergedleavesmostlypresent,petiolate;lamina oblongto lanceolate,decayingearly,sometimesthatof the lowest leaves reducedto phyllodes,45-140 mm long, (5-)10-23 mm wide, 4-7 times as long as wide, brightgreento darkgreen,9-17-veined, with narrow rows of lacunaeborderingthe midrib,minutelydenticulateat margins,cuneateat base, acuteat apex;petiole 30-190(-230) mm long, 0.5-5.0 timesas long as the lamina.Intermediate leaves sometimespresent.Floating Taxonomy of Potamogeton 269 leaves petiolate; lamina oblong to broadly elliptical or obovate, (30-)50-95(-125) mm long, 10-35(-50) mm wide, 2-6 times as long as wide, opaque, coriaceous, brightgreen, sometimes with a reddish tinge, 11-1 9-veined, narrowly cuneate to broadly cuneate at base, acute to obtuse at apex; petiole (45-)80-260(-390) mm long, 0.5-7.0 times as long as the lamina. Stipules axillary, convolute, 40-105 mm long, translucent, persistent. Peduncles 45-105 mm long, 1-3 times as long as the fruiting spike, slightly thicker than the stem, inserted in the axils of floating leaves. Spikes cylindrical, 25-80 mm long in fruit, contiguous. Flowers numerous, with 1-2(-4) carpels. Fruits 2.9-3.7 mm long, dorsal keel more or less distinct. Stem anatomy Stele of trio (1,2) type, endodermis of 0-type, interlacunarbundles absent, subepidermal bundles mostly absent, pseudohypodermis mostly absent, rarely 1-layered. Distribution E and SE Asia, Pacific islands. Hybrids 19 x 21. P. xmalainoides MIKI, WaterPhan. Japan 20. 1937. [= P. distinctusx P. wrightii] Notes (1) P distinctus is closely related to P. nodosus. Because transitional plants are sometimes found it may be regarded in the future as its geographical subspecies (see WIEGLEB1990a). (2) The identity of P xmalainoides might be doubted since it cannot be excluded that its type specimen represents a shallow water form of P. wrightii with floating leaves. However, intermediate forms between the parent species occur without doubt, but their origin has not been satisfactorily explained. 20. Potamogeton nodosus POIRETin LAMARCK, Encycl. Meth. Bot., Suppl. 4: 535. 1816. ("nodosum") P.fluitans proles rothii G. FISCH.,Mitt. Bayer. Bot. Ges. 3(5): 103. 1914. ("Rothii") - P indicus ROXB.,Hort. Bengal. 12. 1814, nom. nud. - P indicus ROXB.in CAREY,Fl. Ind. 1: 471. 1820, nom. illeg. ("indicum"), non ROTHex ROEM.et SCHULT. 1818. P roxburghianus SCHULT. et SCHULT.f., Mant. 3: 367. 1827. ("Roxburghianus") = P petiolaris C. PRESLin J. PRESLet C. PRESL,Delic. Prag. 151. 1822, nom. illeg. ("petiolare"), non P petiolaris RAF. 1811. -P natans subsp. y. petiolaris [C. PRESL]ARCANG.,Comp. Fl. Ital. 642. 1882. -P fluitans proles petiolaris [C. PRESL]GRAEBN.in ENGL.,Pflanzenr. 31 (IV.'1): 59. 1907. - P canariensis LINKin BUCH,Phys. Beschr. Canar. Ins. 138. 1825. P petiolatus WOLFG.in SCHULT.et SCHULT.f., Mant. 3: 352. 1827. - P leschenaultii CHAM.et SCHLTDL., Linnaea 2(2): 223, t. 6. fig. 23. 1827. ("Leschenaultii") = P occidentalis SIEBERex CHAM.et SCHLTDL., Linnaea 2(2): 224. 1827. = P americanus CHAM.et SCHLTDL.,Linnaea 2(2): 226. 1827. = P natans var. angustatus f) americanus (CHAM.et SCHLTDL.) KUNTH,Enum. P1. 3: 128. 1841. = P fluitans subsp. americanus (CHAM.et SCHLTDL.) MAGNIN,Bull. Soc. Bot. France 43: 436. 1896. - P fluitans subsp. americanus (CHAM.et SCHLTDL.) GRAEBN.in ENGL.,Pflanzenr. 31 (IV.l 1): 60. 1907. [isonymum] - P syriacus CHAM.et SCHLTDL., Linnaea 2(2): 227. 1827. P fluitans proles syriacus (CHAM.et SCHLTDL.) GRAEBN.in ENGL.,Pflanzenr. 31 (IV.l 1): 60. 1907. = P marianensis CHAM.et SCHLTDL.,Linnaea 2(2): 228. 1827. = P mascarensis CHAM.et SCHLTDL.,Linnaea 2(2): 228. 1827. P fluitans proles mascarensis (CHAM.et SCHLTDL.) GRAEBN.in ENGL.,Pflanzenr. 31 (IV.I 1): 60. 1907. -P americanus subsp. mascarensis (CHAM.et SCHLTDL.) A. BENN.,J. Bot. 46: 160. 1908. = ? P owaihiensis CHAM.et SCHLTDL.,Linnaea 2(2): 228. 1827. ("O-Waihiensis") -? P. fluitans proles owaihensis (CHAM.et SCI11rDL.)GRAEBN.in ENGL.,Pflanzenr. 31 (IV.11): 60. 1907. = P malaianus MIQ.,Ill. Fl. Archipel Ind. 1: 46. 1870. ("malaina") - P mexicanusA. BENN.,J. Bot. 25: 289. 1887. - ? P peruvianus C. PRESLex A. BENN.,J. Bot. 28: 298. 1890, pro syn. ("peruviana") 270 G. Wiegleb & Z. Kaplan = P delavayiA. BENN.,J. Bot. 30: 228. 1892. ("Delavayi") = P lonchitesvar.novaeboracensisMORONG,Mem.TorreyBot. Club3(2): 20. 1893. = P druceiFRYER,Potamoget.Brit. Isles 31, t. 21. 1898. ("Drucei") = P. semicoloratusA. BENN.,J. Bot. 48: 150. 1910. = P stagnorus HAGSTR.in R.E. FR., Wiss. Ergenb. Schwed. Rhod.-Kongo-Exped. 1911-1912, 1(2): 187. 1916. ("stagnorum") = P. rotundatusHAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5): 153. 1916. = ? P insulanusHAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5): 154. 1916. Description Rhizome slender, terete, perennial, with apical winter buds. Stem unbranched or sparingly branched, slender, terete, annual; specialized dormant turions not developing. Submerged leaves present, absent in landforms, petiolate; lamina narrowly oblong to oblanceolate-oblong, sometimes that of the lowest leaves reduced to phyllodes, (47-)160-280(-350) mm long, (1 -)22-38 mm wide, 5-9 times as long as wide, bright green to dark green, (7-)11-21-veined, with narrow to broad rows of lacunae borderingthe midrib, minutely denticulate at margins, narrowly cuneate at base, acute at apex; petiole (12-)60-180(-250) mm long, 0.2-1.5 times as long as the lamina. Floating leaves present, rarely absent, petiolate; lamina oblong to broadly elliptical, (35-)60-130 mm long, (I1-)25-50 mm wide, 2.0-4.5 times as long as wide, opaque, coriaceous, bright green to olive green, sometimes with a reddish tinge, ( I1-) 15-23-veined, narrowly cuneate to rounded at base, obtuse to broadly acute at apex; petiole 30-210 mm long, 0.5-2.3 times as long as the lamina. Stipules axillary, convolute, (33-)45-125 mm long, translucent, persistent or decaying. Peduncles (32-)45-130 mm long, 2-3 times as long as the fruiting spike, thicker than the stem, inserted in the axils of floating leaves, rarely of submerged leaves. Spikes cylindrical, 25-70 mm long in fruit, contiguous. Flowers numerous, with (2-)4(-5) carpels. Fruits 2.7-4.1(-4.3) mm long, dorsal keel distinct. Stem anatomy Stele of trio (1,2) or proto type, endodermis mostly of 0-type, sometimes of O-U-type, interlacunarbundles absent, rarely a few present, subepidermal bundles absent, rarely a few present, pseudohypodermis absent. Distribution Subcosmopolitan; Europe, Africa, temperate and tropical Asia, Australia, Pacific islands, North America, N and C South America. Hybrids 16 x 20. P. xschreberi G. FISCH., Mitt.Bayer. Bot. Ges. 1(37):471. 1905. ("Schreberi") [= P natansx P nodosus] ? 22 x 20. P. xfaxonii MORONG, Mem.TorreyBot. Club 3(2): 22, t. 32. 1893, pro sp. ("Faxonii") [= ? P illinoensisx P nodosus] P xchamplainiiA. BENN.,J. Bot. 46: 248. 1908. ("Champlainii") - P xrugeliiA. BENN.,J. Bot. 46: 250. 1908, nom. nud. ("Rugelii") Notes (1) P nodosus is one of the most polymorphic Potamogeton species. It shows several regionally distinct morphotypes as well as an extreme phenotypic plasticity all over its range. (2) The southern limits of the distribution of P nodosus in South America and the Malesia-Australia area is unclear.Confusionwith species like P linguatus,P ferrugineus,P. tepperi,andP sulcatusis common. (3) The identity of P owaihiensis is questionable. The original material could not be studied. The name has been placed into the synonymy of P nodosus by several authors. However, broad-leaved specimens from Hawaii collected later are more similar to P solomonensis than to P nodosus. (4) P xfaxonii is provisionally placed here as a hybrid, but its exact identity has not been proved so far. Because of the phenotypic plasticity of the parent species P nodosus hybrids are generally difficult to verify without experimental crossing. 21. Potamogeton wrightii MORONG, Bull. Torrey Bot. Club 13: 158, t. 59. 1886. ("Wrightii") = P mucronatus C. PRESL,Epimel. Bot. 245. 1851. ("1849"), nom. illeg., non SCHRAD.ex SONDER1850. = ? P. sumatranus MIQ., Fl. Ind. Batav., Suppl. 1 [= Fl. Ned. Ind., Eerste Bijv.], 2: 259, 3: 597. 1861. - P japonicus FRANCH. et SAV.,Enum. Pi. Jap. 2: 15. 1877, nom. nud. Taxonomy of Potamogeton - - 271 P tretocarpus MAXIM.ex A. BENN.,J. Bot. 29: 154. 1891, pro syn. P tonkinensis A. CAMUSin LECOMTE,Not. Syst. 1: 86. 1909. - P. distinctusvar.tonkinensis(A. CAMUS) CUONG in CUONG et J.E. VIDAL,Fl. CambodgeLaos Vietnam 20: 58. 1983, nom. inval. P hindostanicus HAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5): 156. 1916. P miyakezimensis HONDA,Bot. Mag. (Tokyo)50: 435. 1936. P jeholensis KITAGAWA, J. Jap.Bot. 44(6): 182. 1969. Description Rhizomeslender,terete,perennial,with apicalwinterbuds.Stemunbranchedor sparinglybranched,slender, terete,annual;specializeddormantturionsnot developing.Submergedleaves petiolate;laminalanceolateor mostly oblong to narrowlyoblong, with parallelmargins,sometimesthat of the lowest leaves reducedto phyllodes,80-200(-310) mm long, (7-)14-20(-27) mm wide,4-10(-17) timesas long as wide,brightgreen to yellow-green,9-13-veined, with narrowrows of lacunaeborderingthe midrib,minutelydenticulateat margins,narrowlycuneateat base, mucronateat apex;petiole(16-)30-70(-140) mm long, 0.1-1.0 times as long as thelamina.Intermediate leavessometimespresent.Floatingleavesusuallyabsentor sometimespresent, petiolate;laminaoblongto elliptical,52-125 mmlong, 12-25 mmwide,2.5-8.0 timesas long as wide,opaque, coriaceous,brightgreen,sometimeswith a reddishtinge, 11-25-veined,cuneateat base, mucronateat apex; petiole 25-135 mm long, 0.5-2.0 times as long as the lamina.Stipulesaxillary,convolute,25-85 mm long, translucent, persistent.Peduncles46-70(-105) mmlong, 1-2 timesas longas thefruitingspike,slightlythicker thanthestem.Spikescylindrical,25-56 mmlong in fruit,contiguous.Flowersnumerous,with4 carpels.Fruits 2.0-3.3 mm long, with a ventralprotrusion,dorsalkeel moreor less distinct. Stem anatomy Steleof trio,rarelyof prototype,endodermismostlyof U-type,sometimes0-type, interlacunar bundlespresent, in 1-2(-3) circles,subepidermal bundlesabsent,rarelya few present,pseudohypodermis present,1-layered. Distribution C, E andSE Asia, Pacific islands. Hybrids 19 x 21. P. xmalainoides MIKI,Water Phan. Japan 20. 1937. [= P distinctus x P. wrightii] 24 x 21. P. xinbaensis KADONO, Acta Phytotax. Geobot. 34(1-3): 54. 1983. [= P lucens x P wrightii] 26 x 21. P. xanguillanus KOIDZ., Bot. Mag. (Tokyo) 43: 398. 1929. [= P perfoliatus x P wrightii] ? P. intortusifolius J.B. HE, L.Y. ZHOUet H.Q. WANG,Bull. Bot. Res. North-East.Forest.Inst. 8(3): 125. 1988. 37 x 21. P. xphilippinensis A. BENN.,PHILIPP. J. SCi. 9: 342. 1914. [= P maackianus x P wrightii] Notes (1) P. wrightiiis a clearlycircumscribedspecies.Nevertheless,confusionhas occurreduntilrecentlywith P lucens, P. distinctus and P. nodosus. (2) The species here called P wrightiiwas generallytreatedunderthe name "P malaianusMIQ."until the typificationof thatnamewas carriedout (WIEGLEB1990b).The typespecimenof P malaianusactuallyrelates to P. nodosus. (3) P sumatranusMIQ.differsfromthe typein certaincharacters(abundant formationof floatingleaves,wider submergedleaves,lowernumberof interlacunar bundles,see WIEGLEB1990bfor details).At presentit cannot be decidedwhetherthis is a regionalmorphotypeof P wrightii,a hybrid,or a species in its own right.In the firstmentionedcase nomenclatural consequencesarise. (4) P xanguillanushasalso beendescribedunderthe informalnamePotamogetonsp. B by LEACH & OSBORNE (1985). (5) P xphilippinensishas been describedfrom a collectionwhich may also containordinaryP maackianus. Lectotypification will be carriedout in the future. 272 G. Wiegleb&Z. Kaplan 22. Potamogeton illinoensis MORONG, Bot. Gaz. (Crawfordsville) 5: 50. 1880. = P. lucens var. connecticutensisJ.W. ROBBINS in A. GRAY,ManualBot. North.U. S. ed. 5. 488. 1867. ("Connecticutensis") P.angustifoliusvar.connecticutensis (J.W.ROBBINS) A. BENN.,J. Bot. 39: 199. 1901.("Connecticutensis") = P lucenssubsp.brasiliensisA. BENN.ex GRAEBN. in ENGL.,Pflanzenr.31 (IV.11): 79. 1907. -P brasiliensis(A. BENN.ex GRAEBN.) A. BENN.,J. Bot. 48: 150. 1910. = P zizii var.il. gracilis A. BENN.ex GRAEBN. in ENGL., Pflanzenr.31 (IV.11): 83. 1907. = P. zizii var.4. porrectifoliusA. BENN.ex GRAEBN. in ENGL.,Pflanzenr.31 (IV.11): 83. 1907. = P curvatusA. BENN.,J. Bot. 46: 249. 1908, pro hybr.P. angustifoliusx P. lucens. = P illinoensisf. rosulatusHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 199. 1916. = P illinoensisf. homophyllusHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 199. 1916. = P fragillimusHAGSTR., Handl.55(5): 202. 1916. Kungl.SvenskaVetenskapsakad. = P macrophylloides HAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 202. 1916. = P pulchelliformisHAGSTR., Ark.Bot. 17(7): 12. 1922. = P pederseniiTUR,Darwiniana24(1-4): 253. 1982. = ? P dunicolaTUR,Darwiniana24(1-4): 254. 1982. Description Rhizomeslenderto robust,terete,perennial,withapicalwinterbuds.Stemunbranched or sparinglybranched, slenderto robust,terete,annual;specializeddormantturionsnotdeveloping.Submergedleavessessileto shortly petiolate;laminanarrowlyoblongor oblanceolateto elliptical,sometimesthatof the lowest leavesreducedto phyllodes,(50-)70-180(-220) mmlong,(4-)15-40(-53) mmwide,3.5-7.0 timesas longas wide,yellow-green to brightgreen,sometimeswith a reddishor brownishtinge, (7-)9-17(-19)-veined, with or withoutnarrow rows of lacunaeborderingthe midrib,minutelydenticulateto entireat margins,cuneateat base, mucronateat apex;petiole0-21(-40) mm long, 0.0-0.2(-0.3) times as long as the lamina.Intermediate leaves sometimes present. Floating leaves present or absent, petiolate; lamina oblong to elliptical or ovate-elliptical, (40-)52-125(-190) mm long, 19-65 mm wide, 1.9-3.1 times as long as wide, opaque,subcoriaceousto coriaceous,yellow-greento darkgreen, sometimeswith a brownishtinge, (11-)13-29-veined, cuneateto roundedor subcordateat base, obtuseor mucronateto acuteat apex;petiole (8-)14-90 mm long, 0.1-0.8 timesas longas thelamina.Stipulesaxillary,convolute,(13-)25-80 mmlong,translucent, persistent.Peduncles 35-130(-310) mm long, 0.8-3.0(-5.0) timesas long as the fruitingspike,as thickas or slightlythickerthan the stem.Spikescylindrical,20-65 mmlong in fruit,contiguous.Flowersnumerous,with(2-)4 carpels.Fruits 2.7-3.6(-3.9) mm long, dorsalkeel distinct. Stem anatomy Stele of protoor trioto oblongtype,endodermisof U-type,rarely0-type, interlacunar bundlespresent,in 1-2 circles, the inner one complete, well developed, subepidermalbundles present, incomplete,or absent, pseudohypodermis present,1-layered,or absent. Distribution NorthAmericaandSouthAmerica. Hybrids ? 22 x 20. P. xfaxonii MORONG, Mem.TorreyBot. Club 3(2): 22, t. 32. 1893, pro sp. ("Faxonii") [= ? P illinoensisx P nodosus] 25 x 22. P xdeminutus HAGSTR., Kungi.Svenska Vetenskapsakad.Handl.55(5): 209. 1916. [= P gramineusx P. illinoensis] ? P. gramineusvar.spathulaeformis J.W.ROBBINS in A. GRAY,ManualBot. North.U. S. ed. 5. 487. 1867. ("spathulxformis") - ? P spathaeformis TUCK.ex J.W.ROBBINS in A. GRAY,ManualBot. North.U. S. ed. 5. 487. 1867,pro syn. ("spatheformis") ? P xspathulaeformis (J.W.ROBBINS) MORONG, Mem.TorreyBot. Club3(2): 26, t. 35. 1893. ? P angustifoliusvar.methyensisA. BENN.,J. Bot. 29: 151. 1891.("Methyensis") - ? P zizii var.methyensisA. BENN.in MACO'IN, Cital. Canad.P1.5: 370. 1890,nom. nud. In ENGL., _ ? P zizii var.methyensis(A. BENN.)GRAEBN. Pflanzenr.31 (IV.l 1): 89. 1907. ? P xmethyensis(A. BENN.)A. BENN.,Trans.& Proc.Bot. Soc. Edinburgh29(1): 50. 1924. - P xpseudolucens HAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 199. 1916. Taxonomy of Potamogeton 273 = P xpseudoziziiHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 210. 1916. ("pseudo-Zizii") Notes (1) P. illinoensisis a polymorphicspecies which has been establishedby North Americanauthorsas an independententitysince the beginningof this century.Nowadaysthe conceptincludesalso plantsfromSouth America.The species is very closely relatedto P lucens. (2) P dunicolais eitheran aberrantformof P illinoensisor a non-floatingleavedformof P linguatus.Stem anatomyseems to justify the first assumption(see TUR1982). 23. Potamogeton schweinfurthii A. BENNETTin DYER, Fl. Trop. Afr. 8: 220. 1901. ("Schweinfurthii") - P capensisSCHEELE ex A. BENN.,Ann. K. K. Naturhist.Hofmus.Wien7: 287. 1892, nom. nud. - P capensis SCHEELE ex A. BENN.in DYER,Fl. Capens. 7: 46. 1897, pro syn. - P lucens var. azoricus A. BENN.,J. Bot. 42: 71. 1904, nom. nud.("azorica") - P azoricus A. BENN.ex HAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5): 198 et 265. 1916, nom. nud. = ? P chamissoi A. BENN.,J. Bot. 42: 74. 1904. ("Chamissoi") = ? P repensHAGSTR. in R.E. FR.,Wiss. Ergenb.Schwed.Rhod.-Kongo-Exped. 1911-1912, 1(2): 185. 1916. = P nodosus var. billotii f. angustissimus HAGSTR.in R. E. FR., Wiss. Ergenb. Schwed. Rhod.-Kongo-Exped. 1911-1912, 1(2): 186. 1916. = P promontoricusHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 182. 1916. = P capensisSCHEELE ex HAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 203. 1916. = P venosus A. BENN.,Trans.& Proc.Bot. Soc. Edinburgh29(1): 52. 1924. Description Rhizomeslender,terete,perennial,withapicalwinterbuds.Stemsparinglyto richlybranched,slender,terete, annual;specializeddormantturionsnot developing.Submergedleaves sessile to shortlypetiolate;lamina narrowly lanceolate to oblong-elliptical, sometimes that of the lowest leaves reduced to phyllodes, 52-170(-235) mm long, (3-)7-28 mm wide, 4-17(-21) timesas long as wide, yellow-greento brightgreen, often with a reddishor brownishtinge, 7-11-veined, with or withoutnarrowrows of lacunaeborderingthe midrib,minutelydenticulate,cuneateat base,mucronateatapex;petiole0-25(-65) mmlong,0.00-0.15(-0.35) timesas long as the lamina.Intermediate leaves sometimespresent,insteadof floatingleaves.Floatingleaves presentor often absent,petiolate;laminaoblongto ellipticalor ovate,43-130 mm long, 12-30 mm wide, 2-6 timesas long as wide, opaque,subcoriaceousto coriaceous,yellow-greento darkgreen,with a reddishtinge, 11-21-veined,cuneateto roundedat base, obtuseto acuteat apex;petiole 14-63 mm long, 0.1-0.6 timesas long as thelamina.Stipulesaxillary,convolute,20-62 mmlong, translucent, persistent.Peduncles35-250 mm long, 2-3 times as long as the fruitingspike, slightlythickerthanthe stem, mostly terminalor lateralin the axils of submergedleaves, sometimesin the axils of floatingleaves. Spikes cylindrical,30-90 mm long in fruit,contiguous.Flowersnumerous,with 4 carpels.Fruits3.0-3.9 mm long, dorsalkeel distinct. Stem anatomy Steleof protoortrioto oblongtype,endodermisof U-type,interlacunar bundlespresent,in 1circle,subepidermal bundlesabsentor scatteredones present,pseudohypodermis present,1-layered. Distribution MascareneIslands,the Azores,Mediterranean Africa,Madagascar, islands?,SW Asia? Hybrids ? 26 x 23. P. xvaginans (BOJER ex A. BENN.)HAGSTR., Kungi. Svenska Vetenskapsakad.Handl.55(5): 280. 1916, pro sp. [= ? P perfoliatus x P schweinfurthii] _ P lucens subsp. vaginans BOJERex A. BENN.,Annuaire Conserv.Jard.Bot. Geneve9: 94. 1905. Notes (1) P schweinfurthii is closely related to P lucens and P illinoensis. It is more widespread than formerly assumed.However,the exactgeographicaldelimitationfromP lucensis unknown,in particularin theAtlantic Islands,the Mediterranean andSW Asia. Transitional formsof unknownstatusareknowne.g. fromPalestine, Greece, and Iraq. 274 G. Wiegleb & Z. Kaplan (2) P chamissoimost probablyrepresentsan apetiolateform of P schweinfurthii.Unfortunately,its type specimenis badlypreserved.Specimenscollectedlaterunderthatnamereferto P nodosus. (3) P xvaginansis provisionallyplaced here as this hybrid.Morphologyand distributionare insufficiently known.As far as is known,it shows a morphologicalvariationpatternanalogousto P xsalicifolius. 24. Potamogeton lucens Linnaeus, Sp. PI. 126. 1753. = Spirilluslucens(L.) NIEUWL.,Amer.Midl.Naturalist3: 17. 1913. = P acuminatus SCHUMACH., Enum.P1. 1: 49. 1801. ("acuminatum") = P lucens [var.]y acuminatus(SCHUMACH.) RCHB.,Icon. Fl. Germ.Helv. 7: 23. 1845. = P longifoliusJ. GAY in LAM.,Encycl. M6th. Bot., Suppl. 4: 535. 1816. ("longifolium") - P lucens subsp. longifolius (J. GAY) MAGNIN,Bull. Soc. Bot. France 43: 440. 1896. = P volhynicus BESSERex ROEM.et SCHULT.,Syst. Veg. ed. 16. 3: 509. 1818. = P cornutus J. PRESLet C. PRESL,Fl. Cech. 37. 1819. ("comutum") _ P caudatus SEIDLex OPIZ,Boheims Phaner. Crypt. Gewachse 23. 1823, nom. illeg. ("caudatum") = P lucens var. P. macrophyllus WALLR.,Sched. Crit. 1: 65. 1822. ("macrophylla") = P macrophyllus WOLFG.in SCHULT.et SCHULT.f., Mant. 3: 358. 1827. = P lucens subsp. macrophyllus (WOLFG.)NYMAN,Consp. Fl. Eur. 4: 682. 1882. = P gaudichaudii CHAM.et SCHLTDL.,Linnaea 2(2): 199. 1827. ("Gaudichaudii") - P lucens var. teganumensis MAKINO,Bot. Mag. (Tokyo) 19: 142. 1905. _ P teganumensis (MAKINO)MAKINO,Bot. Mag. (Tokyo) 26: 122. 1912. = P dentatus HAGSTR.,Bot. Not. 1908: 101. 1908. = P sinicus MIGO,J. Shanghai Sci. Inst., sect. 3, 3: 2. 1934. = P lucens subsp. sinicus (MIGO)HARA,J. Jap. Bot. 60(8): 238. 1985. Description Rhizome slender to robust, terete, biennial to perennial, with apical winter buds. Stem sparingly to richly branched, slender to robust, terete, annual; specialized dormant turions not developing. Submerged leaves shortly petiolate; lamina narrowly oblong to broadly elliptical, sometimes that of the lowest leaves reduced to phyllodes, (49-)70-200(-300) mm long, (10-)25-65 mm wide, (2-)3-6(-10) times as long as wide, yellow-green to bright green, 9-11 -veined, without rows of lacunae borderingthe midrib, denticulate at margins, broadly to narrowly cuneate at base, mucronate at apex; petiole 2-7(-15) mm long, 0.03-0.10 times as long as the lamina. Floating leaves always absent. Stipules axillary, convolute, (20-)30-80(-1 10) mm long, translucent, persistent. Peduncles 50-200(-350) mm long, 2-3(-5) times as long as the fruiting spike, conspicuously thicker than the stem. Spikes cylindrical, 25-70 mm long in fruit, contiguous. Flowers numerous, with 4(-6) carpels. Fruits 3.2-4.5 mm long, dorsal keel distinct. Stem anatomy Stele mostly of oblong type, sometimes of proto or trio type, endodermis of U-type, interlacunar bundles present, multicellular, in 1-3 circles, subepidermal bundles present, often in incomplete circle, pseudohypoderrmispresent, 1-layered. Distribution Europe, N and E? Africa, W, N and E Asia (southwards to Luzon). Hybrids 13 x 24. P. xnervigerWOLFG. in SCHULT. et SCHULT. f., Mant. 3: 359. 1827, pro sp. [= P alpinus x P lucens] 24 x 16. P. xfiuitans ROTH,Tent. Fl. Germ. 1: 72. 1788, pro sp. [= P lucens x P natans] 24 x 21. P. xinbaensis KADONO, Acta Phytotax. Geobot. 34(1-3): 54. 1983. [= P lucens x P wrightii] 25 x 24. P. xangustifolius J. PRESLin BERCHT. et J. PRESL,Rostlinaci 1, fasc. Zabnjkowite 19. 1821, pro sp. [= P gramineus x P lucens] - P zizii MERT.et W.D.J. KOCH,Rohlings Deutschl. Fl. ed. 3. 1: 845. 1823, pro syn. ("Zizii") - P lucens [var.] &.coriaceus MERT.et W.D.J. KOCH,R6hlings Deutschl. Fl. ed. 3. 1: 850. 1823. _ P lucens var. y. amphibius FR., Novit. Fl. Suec. ed. 2. 34. 1828, nom. illeg. Taxonomy of Potamogeton 275 _ P coriaceus (MERT.et W.D.J. KOCH)FRYERex A. BENN.,J. Bot. 24: 223. 1886. = P xzizii W.D.J. KOCHex ROTH,Enum. P1. Phaen. Germ. 1(1): 531. 1827, pro sp. ("Zizii") P gramineus var. y. zizii (W.D.J. KOCHex ROTH)KUNTH,Enum. P1. 3: 131. 1841. ("Zizii") P. heterophyllus var. c. zizii (W.D.J. KOCHex ROTH)BOREAU,Fl. Centre France ed. 3. 2: 600. 1857. ("Zizii") P lucens var. P. zizii (W.D.J. KOCHex ROTH)ASCH.,Fl. Brandenb. 1: 660. 1864. ("Zizii") P lucens subsp. zizii (W.D.J. KOCHex ROTH)NYMAN,Consp. Fl. Eur. 4: 682. 1882. Spirillus zizii (W.D.J. KOCHex ROTH)NIEUWL.,Amer. Midl. Naturalist 3: 19. 1913. ("Zizii") = P lucens var. b. heterophyllus FR., Novit. Fl. Suec. ed. 2. 34. 1828. = P coriaceus FRYER,J. Bot. 27: 8. 1889, nom. illeg., non (MERT.et W. D. J. KOCH)FRYERex A. BENN. 1886. = P. xbabingtonii A. BENN.,J. Bot. 32: 204. 1894. ("Babingtonii") = P xheidenreichii ASCH.et GRAEBN.,Synops. Mitteleur. Fl. 1: 327. 1897. ("Heidenreichii") = P xdecipiens var. berolinensis ASCH.et GRAEBN.,Synops. Mitteleur. Fl. 1: 331. 1897. P berolinensis (ASCH.et GRAEBN.)GRAEBN.,Naturwiss. Wochenschr. 22(6): 361. 1907. ("Berolinensis") 24 x 26. P. xsalicifo/ius WOLFG.in SCHULT. et SCHULT. f., Mant. 3: 355. 1827, pro sp. [= P lucens x P perfoliatus] = P xdecipiens NOLTEex W.D.J. KOCH,Syn. Fl. Germ. Helv. ed. 2. 779. 1844. P lucens var. decipiens (NOLTEex W.D.J. KOCH)HOOK.f., Stud. Fl. Brit. lsl. 372. 1870. - P olivaceus 0. LANG,Flora 29(30): 472. 1846, pro syn. = P decipiens var. affinis A. BENN.,J. Bot. 20: 184. 1882. _ P xaffinis (A. BENN.) P. FOURNIER,Quatre Fl. Fr. 140. 1935. = P upsaliensis TISELIUS,Bot. Not. 1884: 15. 1884. _ P decipiens subsp. upsaliensis (TISELIUS)MAGNIN,Bull. Soc. Bot. France 43: 443. 1896. = P. decipiens var. P. torssanderi TISELIUS,Potamog. Suec. Exs., fasc. 2: [sched.] no. 75. 1895. ("Torssandri") _ P torssanderi (TISELIUS)DORFLER,Herb. Norm. No. 3583. 1898. ("Torssandri") = P salignus FRYERin HIERN,Victoria Hist. Devon. 1: 129. 1906. = P xdecipiens var. y. vollmannii G. FISCH.in E. BAUMANN,Veg. Untersees 105. 1911. ("Vollmanni") - P vollmannii (G. FISCH.)G. FISCH.,Repert. Spec. Nov. Regni Veg. 14(385): 4. 1914, nom. inval. ("Vollmanni") - P xsteriliformis HAGSTR. in HOLMB.,Hartmans Handb. Skand. Fl. 1: 97. 1922, nom. nud. = P xkupfferi A. BENN.,J. Bot. 66: 103. 1928. ("Kupfferi") 35 x 24. P. xcadburyae DANDYet G. TAYLOR, Kew Bull. 12: 332. 1957. [= P crispus x P lucens] Notes (1) P lucens is a distinct species which is easily distinguishable over most of its range. Taxonomic difficulties appear on the southern border of its distribution. (2) The hybrid between P gramineus and P lucens has been called either P xzizii or P xangustifolius. KAPLAN (1997) definitively designated the type of P angustifolius and confirmed its priority. (3) The name P salicifolius has often been misapplied to plants of P. xnitens. In particular,morphotypes called P. torssanderi lead to some confusion causing some authors to assume even triple hybrids among P gramineus, P. lucens, and P perfoliatus. (4) P decipiens has often been wrongly considered to be a result of hybridization of P lucens x P praelongus. The last named hybrid has never been confirmed, even though it was also proposed under various other names. (5) Recently described species P. xinganensis Y.C. MA, Acta Sci. Nat. Univ. Intramongolicae 20(2): 281. 1989, might represent another hybrid of P lucens. 25. Potamogeton gramineus Linnaeus, Sp. PI. 127. 1753. = P heterophyllus SCHREB.,Spicil. Fl. Lips. 21. 1771. Spirillus heterophyllus (SCHREB.)NIEUWL.,Amer. Midl. Naturalist 3: 17. 1913. P gramineus subsp. heterophyllus (SCHREB.)SCHINZet THELL.,Fl. Schweiz ed. 3. 2: 16. 1914. = P hybridus PETAGNA,Inst. Bot. 2: 289. 1787. = P gramineus subsp. hybridus (PETAGNA)ARCANG.,Comp. Fl. Ital. 642. 1882. PI. 276 G. Wiegleb & Z. Kaplan = P augustanusBALB., MWm.Acad. Sci. Turin, Sci. Phys. Math. 1, 10-11 (1802-1803): 330. 1804. ("Augustanum") = P distachyusBELLARDI, MWm.Acad. Sci. Turin,Sci. Phys. Math. 1, 10-11 (1802-1803): 447. 1804. ("distachyum") = P lanceolatusPOIR. in LAM., Encycl.Meth. Bot., Suppl.4: 536. 1816,nom. illeg. ("lanceolatum"), non SM. 1809. P lanciformisROEM. et SCHULT.,Syst. Veg. ed. 16. 3: 512. 1818. - P paucifolius OPIZ,Boheims Phaner. Crypt. Gewachse 23. 1823, nom. nud. - P paucifolius OPIZ,Naturalientausch 223. 1824. P gracilis WOLFG.in SCHULT.et SCHULT.f., Mant. 3: 355. 1827. P wolfgangiiKIHLM. in A. T. SAELAN, KIHLM. et HJELT, Herb.Mus. Fenn.ed. 2. 1: 128. 1889, nom. illeg. ("Wolfgangii") P gramineusproleswolfgangii[KIHLM.] GRAEBN. inENGL.,Pflanzenr.31 (IV.11):89. 1907.("Wolfgangii") P gramineus var. cc. graminifolius FR.,Novit. Fl. Suec. ed. 2. 36. 1828. _ P gramineus subsp. graminifolius (FR.)SCHINZet THELL., Fl. Schweiz ed. 3. 2: 15. 1914. P graminifolius(FR.)FRYERin FRYERet A. BENN.,Potamoget. Brit. Isles 64. 1915. P gramineus var. f. heterophyllus FR.,Novit. Fl. Suec. ed. 2. 37. 1828. - P gramineus [var.] ("spielart")c. heterophyllus G. MEY.,Chloris Han. 520. 1836, nom. illeg., non Fr. 1828. P. nigrescens FR., Novit. Fl. Suec. Mant. 3: 17. 1842. - P rufescenssubsp.nigrescens(FR.)NYMAN, Consp.Fl. Eur.4: 681. 1882. - P kochii 0. LANG, Flora 29(30): 471. 1846, nom. illeg. ("Kochii"), non F W. Schultz 1844. P lonchitesTuCK., Amer.J. Sci. Arts,ser.2, 6: 226. 1848. - P heterophyllus subsp. lonchites (TUCK.)HOOK.f., Stud. Fl. Brit. Isi. 371. 1870. ("lonchitis") - Spirilluslonchites(TUCK.)NIEUWL.,Amer.Midl.Naturalist3: 16. 1913. P latifolius SLOBODA,Rostlinictvf 229. 1852. - P gramineusvar.myriophyllus J.W.ROBBINSin A. GRAY,ManualBot. North.U. S. ed. 5. 487. 1867. = P gramineus var.maximus MORONGex A. BENN., J. Bot. 19: 241. 1881. = P variansMORONG ex FRYER,J. Bot. 25: 308. 1887. = P falcatus FRYER, J. Bot. 27: 65, t. 286. 1889. -P gramineusvar.mongolicusMAXIM.ex A. BENN., J. Bot. 28: 300. 1890, pro syn.; MAXIM. ex A. BENN., - - Bull. Herb. Boissier 4: 546. 1896, pro syn. ? P xseemenii ASCH.et GRAEBN.,Synops. Mitteleur.Fl. 1: 335. 1897, pro hybr.P gramineus x P polygonifolius. ("Seemenii") P biformis HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 247. 1916. ? P sarmaticus MAEMETS,Novosti Sist. Vyssh. Rast. 15: 4. 1979. ("1978") P biformoides PAPCHENKOV, Bot. Zhurn. 82(12): 69. 1997. Description Rhizome slender, rarely filiform, terete, perennial, with apical winter buds. Stem sometimes sparingly to mostly richly branched, filiform to slender, terete, annual; specialized dormant turions not developing. Submerged leaves sessile, linear-oblong or narrowly oblong to oblong or oblanceolate, sometimes that of the lowest leaves reduced to phyllodes, (17-)35-90(-170) mm long, (2-)5-12(-17) mm wide, 4-12(-15) times as long as wide, bright green to dark green, (3-)7-9(-13)-veined, with or without narrow rows of lacunae bordering the midrib, denticulate at margins, cuneate at base, mucronate at apex. Intermediate leaves sometimes present, often as membranous petiolate leaves. Floating leaves present or absent, petiolate; lamina broadly oblong to elliptical or obovate-elliptical, 15-70(-95) mm long, (5-)8-34 mm wide, 1.3-3.6 times as long as wide, opaque, coriaceous, yellow-green to dark green, (7-)1 1-21 (-23)-veined, cuneate to subcordate at base, obtuse to acute at apex; petiole (7-)18-60(-172) mm long, 0.5-4.0 times as long as the lamina. Stipules axillary, convolute, (6-)10-25(-35) mm long, translucent to opaque, persistent. Peduncles (20-)35-100(-350) mm long, usually thicker than the stem, 2-6(-9) times as long as the fruiting spike. Spikes cylindrical, 15-40 mm long in fruit, contiguous. Flowers numerous, with (3-)4(-5) carpels. Fruits 2.4-3.1 mm long, dorsal keel distinct. Stem anatomy Stele of oblong type, endodermis of U-type, interlacunar bundles present, in 1 outer circle, multicellular, subepidermal bundles present or absent, pseudohypodermis absent or present, 1-layered. Taxonomy of Potamogeton 277 Distribution Circumpolar, boreal and temperate regions throughout the Northern Hemisphere. Hybrids 25 x 1. P. xianceolatifolius(TISELIUS)C.D. PRESTON, Watsonia 16(4): 437. 1987. [= P. gramineus x P. polygonifolius] 3 x 25. P. xbillupsii FRYER,J. Bot. 31: 353, t. 337 et 338. 1893. ("Billupsii") [= P coloratus x P gramineus] 13 x 25. P. xnericius HAGSTR.,Kungi. Svenska Vetenskapsakad. Handl. 55(5): 145. 1916. [= P. alpinus x P. gramineus] 25 x 16. P. xsparganiifolius LAEST.ex FR., Novit. Fl. Suec. Mant. 1: 9.1832. ("sparganifolius") [= P gramineus x P. natans] 25 x 22. P. xdeminutus HAGSTR.,Kungi. Svenska Vetenskapsakad. Handl. 55(5): 209. 1916. [= P gramineus x P illinoensis] 25 x 24. P. xangustifolius J. PRESLin BERCHT. et J. PRESL,Rostlinar 1, fasc. Zabnjkowite 19. 1821, pro sp. [= P gramineus x P lucens] 25 x 26. P. xnitens WEBER,Suppi. Fl. Holsat. 5. 1787. [= P gramineus x P. perfoliatus] _ P heterophyllus subsp. nitens (WEBER) HOOK. f., Stud. Fl. Brit. Isl. 371. 1870. = P curvifolius HARTM., Handb. Skand. Fl. 78. 1820. P nitens = = = P xlundii P nipponicus P nitens -P = = P. curvifolius var. MAKINO, f. involutus xinvolutus P xfallax Ill. Fl. Japan ASCH. et GRAEBN., HAGSTR., P. xbiwaensis 1(9): 2, t. 56. Mitteleur. Synops. Kungl. Mag. 1896. Man. Fl. 1: 330. 1897. Brit. Bot. Fl. ed. 2. 1: 504. Vetenskapsakad. (Tokyo) ("involuta") in BAB., Mitteleur. Svenska MIKI, Bot. 1879. 1891. 34: 1, t. 353 et 354. Synops. Fl. ed. 11. 433. Skand. ("Lundii") H. GROVES et J. GROVES ASCH. et GRAEBN., P xfischeri C. HARTM., Handb. 1: 13. 1890. FRYER, J. Bot. (FRYER) = ? P xsubnitens 25 x 37. (HARTM.) K. RICHT., P1. Eur. 48: 326. Handi. 1913. 55(5): ed. 9. 440. 1904. ("Fischeri") 259. 1916. 1934. [= P gramineus x P maackianus] Notes (1) P gramineus great number is another (2) P. sarmaticus also been is most described from (3) No separate taxonomic an independent crossing and Asia, extremely of hybridizations which has polymorphic in which probably a large-leaved Scandinavia value form and North described Delimitation is particularly difficult of the because for P nipponicus. with as of P gramineus. Plants of comparable size have the type result from leaf America. is acknowledged of P gramineus been species. it is involved. the small a separate leaved species The differences form under from of P perfoliatus various names which (e.g. P occurs in East sachalinensis, P juzepczukii). 26. Potamogeton perfoliatus Linnaeus, Sp. PI. 126. 1753. Spirillus - =P perfoliatus P. perfoliatus loeselii P (L.) NIEUWL., var. typicus OGDEN, ROEM. et SCHULT., Syst. perfoliatus [subsp.] Amer. Veg. P. loeselii Midl. Rhodora ed. 45: Naturalist 3: 17. 1913. 177. 1943, nom. 16. 3: 508. 1818. ("Loeselii") (ROEM. et SCHULT.) SCHUBL. inval. et G. MARTENS, Fl. Wurttemb. 110. 1834. ("Loeselii") =P =P - perfoliatus var. a. ovatifolius perfoliatus var. P. rotundifolius [var.] oc. ovalifolius P. perfoliatus Bohm. 1838, - 2(1): nom. P perfoliatus Fl. Bohm. 1838. 251. illeg., 1838; WALLR., MERT. et W.D.J. non WALLR. 251. 1838; ("cordato-lanceolatus") Sched. MERT. et W.D.J. Crit. 1: 66. Crit. 1822. 1: 67. 1822. KOCH ex FIEBER in BERCHT. et OPIZ, Oekon.-Techn. KOCH ex FIEBER in BERCHT. et FIEBER, Potam. Bohmens Fl. 14. 1822. [var.] f. cordatolanceolatus 2(1): Sched. WALLR., MERT. et W.D.J. MERT. et W.D.J. KOCH ex FIEBER in BERCHT. et OPIZ, Oekon-.Techn. KOCH ex FIEBER in BERCHT. et FIEBER, Potam. Bohmens 14. 278 G. Wiegleb & Z. Kaplan = P perfoliatus [var.] y. rotundifolius MERT.et W. D. J. KOCHex FIEBERin BERCHT.et OPIZ,Oekon.-Techn. Fl. Bohm. 2(1): 251. 1838; MERT.et W. D. J. KoCH ex FIEBERin BERCHT.et FIEBER,Potam. Bohmens 14. 1838, nom. illeg., non WALLR.1822. = P perfoliatus var. x. rotundifolius MERT.et W.D.J. KOCHex RCHB.,Icon. Fl. Germ. Helv. 7: 19. 1845, nom. illeg., non WALLR.1822. = P perfoliatus var. x. rotundifolius SONDER,Fl. Hambug. 98. 1850. ("1851"), nom. illeg., non WALLR.1822. = P. perfoliatus var. muelleri A. BENN.,J. Bot. 25: 177. 1887. ("Muelleri") P.perfoliatus subsp. muelleri (A. BENN.)GRAEBN.in ENGL.,Pflanzenr. 31 (IV.11): 95. 1907. ("Muelleri") = P. perfoliatus var. mandschuriensis A. BENN.,Annuaire Conserv. Jard. Bot. Geneve 9: 100. 1905. - P alatofructus A. BENN.,Trans. & Proc. Bot. Soc. Edinburgh 29(1): 49. 1924. = P bupleuroides FERNALD,Rhodora 10: 46. 1908; FERNALDin B.L. ROBINSONet FERNALD,Gray's New Manual ed. 7. 75. 1908. P perfoliatus subsp. bupleuroides (FERNALD)HULTEN,Kungl. Svenska Vetenskapsakad. Hand]., ser. 4, 8(5) [Circump. P1. 1]: 254. 1964. = P perfoliatus var. sachalinensis H. Liv., Repert. Spec. Nov. Regni Veg. 8: 285. 1910. P sachalinensis (H. LEv.) H. LEv., Repert. Spec. Nov. Regni Veg. 10: 441. 1912. = P juzepczukii P DOROF.et TZVELEV,Novosti Sist. Vyssh. Rast. 20: 4. 1983. Description Rhizome slender, terete, perennial, with apical winter buds. Stem unbranchedto richly branched, slender, terete, annual; specialized dormant turions not developing. Submerged leaves sessile, narrowly lanceolate to broadly ovate or orbicular-ovate, 16-115 mm long, 7-42 mm wide, (1.0-)1.3-7.0(-10.0) times as long as wide, yellow-green or bright green to dark green, sometimes with a reddish tinge, (7-)11-25-veined, with narrow rows of lacunae bordering the midrib, denticulate at margins, amplexicaul at base, obtuse to acute and often slightly hooded at apex. Floating leaves always absent. Stipules axillary, convolute, 3-22 mm long, translucent, decaying early. Peduncles 20-110 mm long, 1-5 times as long as the fruiting spike, as thick as or slightly thicker than the stem. Spikes cylindrical, 13-25 mm long in fruit, contiguous. Flowers (6-)9-20, with 4 carpels. Fruits 2.2-3.5(-4.0) mm long, dorsal keel indistinct. Stem anatomy Stele of trio (2) type, with the trio bundle in central position, or rarely of oblong type, endodermis of 0-type, cell wall thickening indistinct or almost absent, interlacunarbundles absent, subepidermal bundles absent or scattered uni-cellular ones present, pseudohypodermis absent or partly present, I-layered. Distribution Europe, N and C Africa, Asia, Australia, E North and C America. Hybrids 13 x 26. P. xprussicus HAGSTR., Bot. Not. 1908: 103. 1908. [= P alpinus x P perfoliatus] 26 x 21. P. xanguillanus KOIDZ., Bot. Mag. (Tokyo) 43: 398. 1929. [= P perfoliatus x P wrightii] 24 x 26. P xsalicifolius WOLFG.in SCHULT. et SCHULT. f., Mant. 3: 355. 1827, pro sp. [= P lucens x P perfoliatus] ? 26 x 23. P. xvaginans (BOJERex A. BENN.)HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 280. 1916, pro sp. [= ? P perfoliatus x P schweinfurthii] 25 x 26. P xnitens WEBER,Suppi. Fl. Holsat. 5. 1787. [= P gramineus x P perfoliatus] 26 x 28. P. xcognatus ASCH.et GRAEBN., Synops. Mitteleur. Fl. 1: 317. 1897. [= P perfoliatus x P praelongus] - P xintermixtus A. BENN.,J. Bot. 41: 166. 1903. 35 X 26. P. xcooperi (FRYER)FRYER,Bot. Exch. Club Brit. Isles Rep. 1: 497. 1897; (FRYER)FRYER,J. Bot. 35: 311. 1897. ("Cooperi") [= P. crispus x P perfoliatus] P undulatus var. cooperi FRYER,J. Bot. 29: 289, t. 313. 1891. ("Cooperi") Taxonomy of Potamogeton 279 P. xcymatodesAsCH. et GRAEBN., Synops.Mitteleur.Fl. 1: 337. 1897,nom. illeg. = ? P xcymbifolius G. FISCH.,Mitt. Bayer.Bot. Ges. 1(31):366. 1904. 37 x 26. P. xleptocephalus KOIDZ. in Y. DoI, Fl. Satsum. 2: 162. 1931. [= P maackianus x P perfoliatus] - P nakamurai YAMAUCHI et MoMIY., Rep. Faun.Fl. LakeKasumigaura 7. 1971, nom. nud. 26 x 48. P. xmysticus MORONG, Bot. Gaz. (Crawfordsville) 5: 50. 1880, pro sp. [= P. perfoliatus x P pusillus] Note (1) P.juzepczukii,like otherP. perfoliatus-forms fromEastAsia, shows certaindeviantcharactersbutin total morphologicaldelimitationis indistinct. 27. Potamogeton richardsonii (A. BENNETT)RYDBERG,Bull. Torrey Bot. Club 32: 599. 1905. ("Richardsonii") P.perfoliatus var.lanceolatus J.W. ROBBINSin A. GRAY,ManualBot. North.U. S. ed. 5. 488. 1867,nom. illeg., non BLYTT1861. P perfoliatus var.richardsonii A. BENN.,J. Bot. 27: 25. 1889. ("Richardsonii") P perfoliatus proles loeselii var. cordatolanceolatus subvar. richardsonii (A. BENN.)ASCH.et GRAEBN., Synops.Mitteleur.Fl. 1: 314. 1897. - Spirillus perfoliatus var. richardsonii (A. BENN.)NIEUWL.,Amer. Midl. Naturalist 3: 17. 1913. P perfoliatus subsp. richardsonii (A. BENN.)HULTEN,Fl. Alaska Yukon 1: 102. 1941. P perfoliatus subsp. richardsonii (A. BENN.)E. MURRAY,Kalmia 12: 23. 1982. [isonymum] Description Rhizomeslender,terete,perennial,withapicalwinterbuds.Stemsparinglyto richlybranched,slender,annual; specializeddormantturionsnot developing.Submergedleavessessile,narrowlylanceolateto ovate-lanceolate, (15-)30-100 mm long, 5-19 mm wide, 2.5-7.0 times as long as wide, yellow-green to dark green, (7-) l 3-25(-33)-veined, withnarrowrowsof lacunaeborderingthemidrib,denticulateat margins,amplexicaul at base, narrowlyobtuse to acute but not hoodedat apex. Floatingleaves always absent.Stipulesaxillary, convolute, 8-26 mm long, opaque, fibrous, decaying but remaining as whitish fibres. Peduncles (14-)20-100(-250) mm long, 0.9-6.0 times as long as the fruitingspike,as thickas or slightlythickerthan the stem. Spikes cylindrical,8-30(-40) mm long in fruit,contiguous.Flowers7-17, with 4 carpels.Fruits 2.7-4.2 mm long, dorsalkeel indistinct. Stem anatomy Stele of triotype,withthe triobundlesin centralposition,endodermisof 0-type, cell wall thickeningindistinct or almostabsent,interlacunar absentorpartly bundlesabsent,subepidermal bundlesabsent,pseudohypodermis 1-layered. Distribution NorthAmerica. Note (1) P richardsoniiis closely relatedto P perfoliatus.They arepartlyvicariantin theirdistribution. 28. Potamogeton praelongus WULFEN in ROEMER, Arch. Bot. 3(3): 331. 1805. E P acuminatusWAHLENB., Fl. Upsal.58. 1820, nom. illeg. ("acuminatum") = P lucens [var.]("spielart") a. corniculatusG. MEY.,ChlorisHan.522. 1836. = Spirillus praelongus (WULFEN)NIEUWL.,Amer.Midl. Naturalist3: 17. 1913. = P flexuosus WREDOW,Oekon.-Techn.Fl. Meklenb.1: 255. 1811. = P perfoliatus var.lacustris WALLMANin LILJ.,UtkastSv. Fl. ed. 3. 706. 1816. = P gramineusvar.a. borealisLAEST.,Kongl.SvenskaVetenskapsakad. Handl.1824: 162. 1824. ("boreale") = P praelongus var.brevifolius CELAK.,Sitzungsber.Konigl.Bohm. Ges. Wiss. Prag,Math.-Naturwiss. Cl. 1886: 11. 1886. = P praelongus var.6. angustifolius GRAEBN.in ENGL.,Pflanzenr.31 (IV.11): 97. 1907. = P praelongus f. pygmeus GALINISin NATKEVICAITE-IVANAUSKIENE, Liet. TSR Flora 2: 677. 1963. 280 G. Wiegleb & Z. Kaplan Description Rhizomeslenderor robust,terete,perennial,with apical winterbuds and overwinteringshortshoots. Stem unbranched to richlybranched,slenderto robust,terete,annualto perennial;winterbudsas axillary,short,leafy shoots, specialized dormantturions not developing. Submergedleaves sessile, narrowlylanceolate to lanceolate-ovate,(45-)60-180(-360) mm long, 14-40 mm wide, (2.5-)3.0-7.5(-l 1.0) timesas long as wide, brightgreento darkgreen, 11-19(-25)-veined, with narrowrows of lacunaeborderingthe midrib,entireat margins,roundedand semiamplexicaulat base, obtuseanddistinctlyhoodedat apex. Floatingleaves always absent.Stipulesaxillary,convolute, 10-80 mm long, translucentwhen fresh, opaquewhen dry, persistent. Peduncles(50-)80-250(-800) mmlong, 2-7(-9) timesas long as the fruitingspike,as thickas or thickerthan the stem.Spikescylindrical,20-80 mmlong in fruit,contiguous.Flowersnumerous,with(2-)4 carpels.Fruits (3.8-)4.5-5.5 mm long, dorsalkeel distinct. Stem anatomy Stele of prototype, endodermisof U-type,rarely0-type, interlacunar bundlespresent,in 2-3 circles,strong, subepidermal bundlespresent,pseudohypodermis present,1-3-layered. Distribution Circumboreal, throughoutthe northernhemisphere. Hybrids 13 x 28. P. xgriffithiiA. BENN.,J. Bot. 21: 65, t. 235. 1883. ("Griffithii") [= P. alpinus x P praelongus] 26 x 28. P. xcognatus ASCH. et GRAEBN., Synops. Mitteleur. Fl. 1: 317. 1897. [= P perfoliatus x P praelongus] 35 x 28. P. xundulatus WOLFG. in SCHULT.et SCHULT.f., Mant. 3: 360. 1827, pro sp. [= P crispus x P praelongus] 29. Potamogeton epihydrus RAFINESQUE,Med. Repos., Hexade 3, 2: 409.1811.. ("epihydrum") - P epihydrus var.typicus FERNALD, Mem.Amer.Acad.ArtsSci. 17(1): 114. 1932, nom. inval. - P epihydrusRAF.,Med. Repos.,Hexade2, 5: 354. 1808, nom. prov.("epihydrum") = P. nuttallii CHAM.et SCHLTDL., Linnaea2(2): 226, t. 6, fig. 25. 1827. ("Nuttalii") -P. epihydrus var.nuttallii (CHAM. et SCHLTDL.) FERNALD, Mem.Amer.Acad.ArtsSci. 17(1): 115. 1932. = P epihydrussubsp. nuttallii(CHAM.et SCHLTDL.) CALDER et R.L. TAYLOR, Canad.J. Bot. 43: 1388. 1965. = P pennsylvanicusWILLD. ex CHAM.et SCHLTDL., Linnaea2(2): 227. 1827. ("pensylvanicus") = P pumilus WOLFG. in SCHULT. et SCHULT. f., Mant.3: 354. 1827. = P claytonii TUCK., Amer.J. Sci. Arts,ser. 1, 45: 38. 1843. ("Claytoni") = P nuttallii var.ramosus PECK, AnnualRep. New YorkStateMus. 47: 162. 1894. = P epihydrus var. ramosus (PECK) H.D. HOUSE,New York State Mus. Bull. 254: 52. 1924. = P nuttallii var.cayugensis WIEGAND, Rhodora2: 102. 1900. ("Cayugensis") -P epihydrus var.cayugensis (WIEGAND) A. BENN., J. Bot. 42: 69. 1904. ("Cayugensis") =P cayugensis(WIEGAND)HAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5): 140. 1906. = P tennesseensis FERNALD, Rhodora38: 167. 1936. Description Rhizomeslenderto robust,compressed,perennial,withapicalscalywinterbuds.Stemunbranched or sparingly branched,slenderto robust,compressedto teretetowardsthe apex, annual;specializeddormantturionsnot developing.Submergedleaves sessile, often markedlydistichous,linearto ribbon-like,65-240 mm long, (1.0-)2.5-1 1.0 mm wide, 18-30(-60) times as long as wide, brightgreen to olive green or brown-green, sometimeswitha reddishorbrownishtinge,5-9(-1 3)-veined,withbroadrowsof lacunaeborderingtheniidrib, entireat margins,straightto narrowlycuneateat base, narrowlyobtuseto acuteat apex. Intermediate leaves sometimespresent,shortpetiolate;petioleoftenflattened.Floatingleavespetiolate;laminaoblongto elliptical, 35-80 mmnlong, 7-22 mm wide, 2.5-5.0 times as long as wide, opaque,coriaceous,brown-greento dark green,9-21-veined, cuneateat base,obtuseat apex;petiolenot flattened,20-60(-90) mm long,0.5-2.0 times as long as the lamina.Stipulesaxillary,convolute,10-45 mm long, translucent,decayingearly.Peduncles 23-90 mm long, 1.5-4.0 times as long as the fruitingspike,usuallyas thickas the stem, mostly insertedin the axils of floating leaves, rarelyin the axils of, or suboppositeto, submergedleaves. Spikes cylindrical, Taxonomy of Potamogeton 281 10-30 mm long in fruit, contiguous. Flowers 11-18, with 4 carpels. Fruits 2.5-3.1(-4.0) mm long, dorsal keel indistinct. Stem anatomy Stele of eight bundles or oblong to four bundles type, endodermis of 0-type, interlacunar bundles absent or scattered ones present, subepidermal bundles absent or scattered ones present, pseudohypodermis absent. Distribution North America, NW Europe (British Isles). 30. Potamogeton ulei K. SCHUMANN in MARTIUS, Fl. Bras. 3(3): 690. 1894. ("Ulei") = ? P sclerocarpus K. SCHUM.in MART.,Fl. Bras. 3(3): 688. t. 120, fig. 2. 1894. = P paramoanusR.R. HAYNESet HOLM-NIELS., Syst. Bot. 7(4): 498. 1982. Description Rhizome slender, compressed, perennial, with apical winter buds. Stem unbranched, slender, terete to slightly compressed, annual; specialized dormant turions not developing. Submerged leaves sessile, linear, 35-265 mm long, 1.0-4.1 mm wide, 25-70 times as long as wide, bright green to olive green or brown-green, sometimes with a reddish or brownish tinge, 3-7-veined, with broad rows of lacunae bordering the midrib, entire at margins, straight at base, narrowly obtuse to acute at apex. Intermediate leaves often present. Floating leaves mostly present, petiolate; lamina oblong to elliptical, 14-31 mm long, 6-9 mm wide, 2-4 times as long as wide, opaque, coriaceous, brown-green to dark green, 5-9-veined, narrowly cuneate at base, acute to obtuse at apex; petiole 14-44 mm long, 0.8-1.5 times as long as the lamina, mostly flattened. Stipules axillary, convolute, 5-26 mm long, translucent, decaying early. Peduncles 11-27 mm long, 1.5-2.5 times as long as the fruiting spike, as thick as or thinner than the stem, inserted in the axils of both floating and submerged leaves. Spikes cylindrical, 6-14 mm long in flower, contiguous. Flowers 12-18, with 4 carpels. Fruits 2.3-2.7 mm long, dorsal keel distinct. Stem anatomy Stele of four bundles type, endodermis of 0-type, interlacunarbundles absent, rarely present, subepidermal bundles present, pseudohypodermis present (1-layered?). Distribution N and NE South America. Notes (1) P ulei is closely related to P epihydrus. (2) Since its original introduction, P ulei has always been considered as a homophyllous species similar to P polygonus. However, the leaf anatomy of the original collection ULE 1919 (HBG), with their well developed lacunae and abundantanastomoses, clearly points these plants to the P epihydrus-group.In addition, isolectotype plants have well developed floating leaves, by which character they are definitively distinguished from P polygonus. (3) P sclerocarpus shows certain deviating characters in its general appearance and stem anatomy. We are inclined to presume that such named plants represent deep-water forms of P ulei, since both the morphotypes share many important distinguishing characters, especially in leaf anatomy. 31. Potamogeton montevidensis A. BENNETT, Ann. K. K. Naturhist. Hofmus. Wien 7(4): 293. 1892. Description Rhizome slender, terete, perennial, non-dormant scaly winterbuds present. Stem unbranched, slender, terete, annual;specialized dormantturions not developing. Submerged leaves sessile; lamina linear-lanceolate to linear, mostly decaying early, 70-100 mm long, 4-6 mm wide, 14-21 times as long as wide, bright green to brown-green, 5-9-veined, with broad rows of lacunae bordering the midrib, entire at margins, straight to narrowly cuneate at base, acute at apex. Intermediaiteleaives sometimes present, petiolate, lanceolate. Floating leaves petiolate; lamina oblong or lanccolate to obovate, 33-50(-65) mm long, (5-)15-20(-25) mm wide, 2.1-4.5(-6.6) times as long as wide, opaque, corialceOus, bright green to brown-green, 11-15(-17)-veined, cuneate at base, rounded or subacute at apex; petiole flattened, 40-115(-150) mm long, 1.1-2.5 times as long as the lamina. Stipules axillary, convolute, 20-35 mm long, translucent,decaying early. Peduncles 40-100 mm 282 G. Wiegleb & Z. Kaplan long, 2-5 timesas long as the fruitingspike,as thickas or slightlythinnerthanthe stem,insertedas lateralor terminalin the axils of floatingleaves, or rarelysuboppositeto floatingleaves. Spikescylindrical,10-30 mm long in fruit,contiguous.Flowers 1-13, with4 carpels.Fruits3.0-3.5 mm long, dorsalkeel distinct. Stem anatomy Stele of trioor complex4 bundlestype, endodermisof 0-type or faintU-type,interlacunar bundlesabsentor 1 circlepresent,subepidermalbundlespresentas incompletecircle,pseudohypodermis absent. Distribution Argentina,Uruguay,Brazil. Note (1) P. montevidensisis closely relatedto P. epihydrusand to P ulei. Delimitationis indistinctdespitethe geographicaldistance. 32. Potamogeton drummondiiBENTHAM in BENTHAM et F. MUELLER, Fl. Austral. 7: 171. 1878. ("Drummondii") = ? P similisA. BENN.,J. Bot. 40: 146. 1902. Description Rhizomefiliformto slender,terete,perennial,winterbudsnot seen. Stemunbranched, slender,terete,annual; specializeddormantturionsnot developing.Submergedleaves sessile to shortlypetiolate;laminanarrowly oblong to lanceolateor broadlyovate, 40-120 mm long, 5-20 mm wide, 2-12 times as long as wide, pale green,3-1 1-veined,withnarrowrowsof lacunaeborderingthemidrib,entireat margins,cuneateatbase,acute at apex;petiole0-5 mm long, 0-0.05 timesas long as the lamina.Floatingleavespresentor absent,petiolate; laminaellipticalto broadlyelliptical,20-40 mm long, 12-25 mm wide, 1.2-2.0 timesas long as wide,opaque, coriaceous,yellow-greento olive green,9-15-veined,broadlycuneateatbase,acuteatapex;petiole(10-)35-80 mm long, (0.3-)1.0-2.4 times as long as the lamina.Stipulesaxillary,convolute,16-25 mm long, translucent, persistent.Peduncles30-90 mm long, 4-6 times as long as the fruitingspike, slightlythickerthanthe stem, insertedin the axils of floatingandsubmergedleaves.Spikessubgloboseto cylindrical,7-22 mm long in fruit, contiguous.Flowers 10-16, with 4 carpels.Fruits1.7-2.0(-2.5) mm long, dorsalkeel distinct,lateralkeels indistinct. Stem anatomy Stele mostlyof fourbundlestype, sometimesof protoor triotype,endodermisof 0-type, interlacunar bundles absent or present in 1 incompletecircle, subepidermalbundlesusually absent, rarelyfaint ones present, pseudohypodermis absentor partlypresent. Distribution Westemand SouthernAustralia,Tasmania. Note (1) P. drummondiiis not sufficientlyknown as to the rangeof its characters.It is eitheranotherextremely polymorphicspecies or it consists of two independenttaxa.The "holotype"Drummond,Nova Hollandia,is of uncertainorigin, and has relativelywell-developedsubepidermalbundles.RAUNKIAER(1903) found no such bundles,only single strands,althoughHAGSTROM (1916) did. In the specimeninvestigated(fromC) it wasdifficultto decidewhatone can reallysee. Therearesomebundlesbutwhethertheyaretrulysubepidermal or the outerinterlacunar ones cannotbe discerned.The presentdescriptionis basedon recentspecimensonly (Weston80-44, PERTH;Gardner1372, PERTH;Orchard4356, PERTH;Strid21233, B, C, PERTH;Strid 21234, B, C, M; Meebold2/27, M). Withinthese specimenstwo morphotypesexist, one with lanceolateand one with oblong submergedleaves. The oblongmorphotypealways lacks subepidermal bundles.Cultivation experimentsare necessaryto clarifythe statusof the morphotypes. 33. Potamogeton cheesemanii A. BENNETT, J. Bot. 21: 66. 1883. ("Cheesemanii") - P oblongifoliusKIRKex HOOK. f., Handb.New Zeal. Fl. 2: 742. 1867, nom. nud. - P. natansvar.australisKIRKex A. BENN.,J. Bot. 25: 177. 1887, pro syn.; KIRK ex A. BENN.,Ann. K. K. Naturhist.Hofmus.Wien7: 286. 1892,pro syn. = ? P tricarinatusF. MUELL. et A. BENN.,J. Bot. 30: 229. 1892. = ? P samariformis HAGSTR.,Kungl.SvenskaVetenskapsakad. HandI.55(5): 166. 1916. 283 Taxonomy of Potamogeton = = = = ? P sessilifolius HAGSTR., Handl.55(5): 167. 1916. Kungl.SvenskaVetenskapsakad. P porrigens HAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 172. 1916. Handl.55(5): 174. 1916. P cheesemanii f. tasmanicus HAGSTR.,Kungl.SvenskaVetenskapsakad. ? P. cheesemanii f.frondosus HAGSTR., Handl.55(5): 174. 1916. Kungl.SvenskaVetenskapsakad. Description Rhizomefiliformto slender,terete,perenial,winterbudsnot seen. Stem unbranchedor sparinglybranched, slender,terete,annual;specializeddormantturionsnot developing.Submergedleaves sessile or subsessileto shortlypetiolate;laminanarrowlylinear-lanceolate or narrowlyelliptical,relativelyuniform,40-100 mmlong, 5-15 mm wide, 6-12 times as long as wide, brightgreento darkgreen, sometimeswith a brownishtinge, 5- 1-veined, with narrowrows of lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base, roundedto emarginateor subacuteat apex;petiole0-5(-30) mm long, 0.00-0.05(-0.30) times as long as the lamina.Intermediate leaves sometimespresent,petiolate,lanceolateto lanceolate-spathulate; petioleup to 20 mm long. Floatingleavespresentor absent,petiolate;laminaovateto elliptical-oblong,20-45(-58) mm long, 10-26 mm wide, 1.3-3.3 times as long as wide, opaque,coriaceous,yellow-greento olive green,sometimes with a brownishtinge, (5-)9-1 5(-17)-veined,roundedor truncateto subcordateat base, roundedto subacute at apex;petiole(15-)30-80 mm long, (0.3-)1.5-3.2 timesas long as the lamina.Stipulesaxillary,convolute, (13-)24-35 mm long, translucent,decayingor persistent.Peduncles(23-)40-60 mm long, 2.5-4.0 times as long as the fruitingspike,as thickas the stem,insertedin the axilsof floatingleaves.Spikescylindrical,10-25 mm long in fruit, contiguous.Flowers 16-numerous,with 4 carpels.Fruits2.0-2.6 mm long, dorsalkeel distinct,lateralkeels distinct. Stem anatomy Stelemostlyof fourbundlestype,sometimesof protoortriotype,withstrongcentralsclerenchyma,endodermis of 0-type, rarelyO-U-type,interlacunar bundlesabsentor outercirclepresent,subepidermal bundlespresent, mostlystronglydeveloped,pseudohypodermis absent. Distribution New Zealand,Australia,Tasmania. Notes (1) In the presenttreatmentP cheesemanii is conceivedas a species comprisinga wide rangeof divergent morphotypes.Becauseof thispolymorphismthe wide distribution of P cheesemanii has beenoverlookeduntil recently.ConfusionwithP. sulcatus (underP tricarinatus), P australiensis, P drummondii, andP suboblongus has occurred.The ultimateidentityof several synonyms(P sessilifolius, P samarifonnis, also P similis) dependson the choice of lectotypesin the futureand the exact delimitationbetween P cheesemanii and P drummondii. So far unrecognizedhybridization may be anothercause of confusion. (2) Thename"P tricarinatus" has beenappliedto almostanybroad-leavedPotamogeton speciesof Australia. In the strictsense however,P tricarinatus may be regardedas a species in its own right.In theirtreatment submittedto Flora of Australia,Papassotiriou,Jacobsand Hellquistprovidea shortdescription.The plant resemblesP cheesemanii in generalhabitbut is closer to P sulcatus with respectto fruitshape.The plantis rare,andobviouslyrarelycollectedanddistributedamongtheherbaria.At presentthereis notenoughmaterial availableto providea fully satisfactorydescription. 34. Potamogeton solomonensis WIEGLEB, Blumea 37: 381. 1993. Description Rhizomeslender,terete,perennial,winterbudsnot seen. Stemunbranched, slender,terete,annual;specialized dormantturionsnot developing.Submergedleaves mostlypetiolate,sometimessubsessile;laminalanceolate to ribbon-like,partlyfalcate,80-135(-150) mm long, 5-8(-15) mm wide, 8-19 timesas long as wide,bright greento darkgreen,3-5-veined, withnarrowrowsof lacunaeborderingthemidrib,entireat margins,narrowly cuneateatbase,acuteat theapex;petiole(0-)20-50 mmlong,(0-)0.2-0.4 timesas longas thelamina.Floating leaves presentor absent,petiolate;laminaoblongto lanceolate,35-45 mm long, 12-18 mm wide, 2.3-3.1 times as long as wide, opaque,coriaceous,yellow-greento olive green, 9-1 1-veined, narrowlyto broadly cuneateat base, obtuse to subacuteat apex; petiole 40-80 mm long, 1.7-4.0 times as long as the lamina. Stipulesaxillary,convolute,20-30 mm long, translucent,persistent.Inflorescencesdimorphic.Peduncleof apical inflorescencesinsertedin the axils of floatingleaves, 40-60 mm long, 2.5-4.0 times as long as the floweringspike, as thick as the stem;peduncleof lateralinflorescencesinsertedin the axils of submerged 284 G. Wiegleb & Z. Kaplan leaves or suboppositeto submergedleaves, 10 mm long, withthe spike6 mm long, oftenundeveloped.Spikes dimorphic,cylidricalor subglobose,(6-)10-15 mm long in flower,contiguous.Flowersnumerous,with 4 carpels.Ripe fruitsnot seen. Stem anatomy Stele of reducedtrio or four bundlestype, endodermisof 0-type, interlacunar bundlesabsent,subepidermal bundlesabsent,pseudohypodermis absentor present,1-layered. Distribution SolomonIslands,New Caledonia. Note (1) P solomonensis is closely related to P cheesemanii. 35. Potamogeton crispus Linnaeus, Sp. PI. 126. 1753. - P crispus var. a. genuinus RCHB.,Icon. Fl. Germ. Helv. 7: 18. 1845, nom. inval. - P tuberosus ROXB.,Hort. Beng. 12. 1814, nom. nud. ("tuberosum") P tuberosus ROXB.in CAREY,Fl. Ind. 1: 472. 1820. ("tuberosum") P serrulatusOPIZ,Flora5: 267. 1822, nom.nud.;OPIZ,BoheimsPhaner.Crypt.Gewachse23. 1823,nom. nud.("serrulatum") = P crenulatus D. DON, Prodr. Fl. Nepal. 22. 1825. ("crenulatum") - - P crispatus WALLMANex FR., Novit. Fl. Suec. ed. 2. 43. 1828, pro syn. = P crispus [var.] ("spielart")a. planifolius G. MEY., Chloris Han. 523. 1836. P. crispus [var.]a. acutifolius FIEBERin BERCHT.et OPIZ,Oekon.-Techn. Fl. Bohm.2(1): 269. 1838;FIEBER in BERCHT.et FIEBER,Potam. Bobhmens32. 1838. = P crispus[var.]P. obtusifoliusFIEBERin BERCHT.et OPIZ,Oekon.-Techn. Fl. Bohm. 2(1):269.1838;FIEBER - in BERCHT. et FIEBER, Potam. Bohmens 32. 1838. = P crispusvar.P. gemmiferRCHB.,Icon. Fl. Germ.Helv.7: 18, t. 30, fig. 51. 1845. = P crispus var. Y. serrulatus SCHRAD.ex RCHB.,Icon. Fl. Germ. Helv. 7: 18, t. 30, fig. 52. 1845. = P lactucaceus MONTANDON,Guide Bot. Sundgau [= FRICHE-JOSET, Syn. Fl. Jura ed. 2.] 305. 1868. ("lactucaceum") = P hohenackeri GAND.,Oesterr.Bot. Z. 31: 43. 1881. ("Hohenackeri") = P hungaricus GAND.,Oesterr. Bot. Z. 31: 43. 1881. = P pallidior GAND.,Oesterr. Bot. Z. 31: 43. 1881. = P rubricans GAND.,Oesterr. Bot. Z. 31: 43. 1881. = P austriacus GAND.,Oesterr. Bot. Z. 31: 44. 1881. = P leptophyllus GAND.,Oesterr. Bot. Z. 31: 44. 1881. = P macrorrhynchus GAND.,Oesterr. Bot. Z. 31: 44. 1881. _ P crispus var. macrorrhynchus (GAND.)ASCH. et GRAEBN.,Synops. Mitteleur. Fl. 1: 336. 1897. = P notarisiiGAND.,Oesterr.Bot. Z. 31: 44. 1881. ("Notarisii") = P rubrinaevus GAND.,Oesterr. Bot. Z. 31: 44. 1881. Description Rhizomefiliformto slender,compressed,annualor biennial.Stemunbranched or sparinglybranched,filiform to slender,compressed,bicanaliculate,annualor partlywintergreen;stiff axillarynon-dormantturionsof variousshapesdevelopingthroughoutthe growthseason.Submergedleaves sessile, linearto linear-oblong, 25-95(-132) mm long, (4-)6-12(-18) mm wide, 5-9(-13) timesas long as wide, brightgreento darkgreen, oftenwitha reddishtinge,(3-)5(-7)-veined, withnarrowto broadrowsof lacunaeborderingthemidrib,serrate and usuallystronglyundulateat margins,broadlycuneateat base, obtuseto acute at apex. Floatingleaves alwaysabsent.Stipulesaxillary,convoluteto shortlyconnate,4-12(-17) mm long,translucent, decayingearly. Peduncles14-65(-125) mmlong,3-8 timesas longas thefruitingspike,as thickas thestem.Spikescylindrical, 5-16 mmlong in fruit,contiguousto shortlydistant.Flowers3-8, with(2-)4 carpels.Fruits4.0-6.2 mmlong, adnateat base,dorsalkeel distinct,beakvery prominent,0.5-0.8 timesas long as the restof the fruit. Stem anatomy Stele of oblong type, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundles absent, pseudohypodermis present,1-layered,or absent. Taxonomy of Potamogeton 285 Distribution Europe, Africa, Asia, Australia, introduced in New Zealand, North America and S South America. Hybrids 13 x 35. P. xolivaceus BAAGOE ex G. FISCH.,Ber. Bayer. Bot. Ges. 11: 33. 1907. [= P alpinus x P. crispus] 35 x 24. P. xcadburyae DANDYet G. TAYLOR, Kew Bull. 12: 332. 1957. [= P. crispus x P. lucens] 35 x 26. P. xcooperi (FRYER) FRYER, Bot. Exch. Club Brit. Isles Rep. 1: 497. 1897; (FRYER)FRYER,J. Bot. 35: 311. 1897. ("Cooperi") [= P crispus x P. perfoliatus] 35 x 28. P. xundulatus WOLFG.in SCHULT. et SCHULT. f., Mant. 3: 360. 1827, pro sp. [= P crispus x P praelongus] 35 x 47. P xlintonii FRYER,J. Bot. 38: 366. 1900; FRYER,Bot. Exch. Club Brit. Isles Rep. 1899-1900: 21. 1900. ("Lintoni") [= P crispus x P friesii] 35 x 55. P. xbenneffii FRYER,J. Bot. 33: 1, t. 348. 1895. ("Bennettii") [= P. crispus x P trichoides] Note (1) P crispus exhibits extreme morphological variation. Despite this fact it is always easily recognizable as being the most distinct species within the genus. 36. Potamogeton robbinsii OAKES,Mag. Hort. Bot. 7(5): 180. 1841. ("Robbinsii") _ Spirillus robbinsii (OAKES) NIEUWL., Amer. Midl. Naturalist 3: 19. 1913. ("Robbinsii") - P pumilus NuTT. ex A. BENN., Ann. K. K. Naturhist. Hofmus. Wien 7: 292. 1892, pro syn. ("pumilum") Description Rhizome slender, terete, perennial. Stem sparingly branchedbelow, richly branchedupwards, filiform to slender, terete, annual; axillary or apical dormant turions developing. Submerged leaves sessile, linear to lanceolate, 25-80(-120) mm long, (2-)3-6(-8) mm wide, 7-15 times as long as wide, dark green, 5-7-veined, with 20-72 additional sclerenchymatous strands, without rows of lacunae bordering the midrib, mostly serrulateat margins, auriculate at base, acute at apex. Floating leaves always absent. Stipules adnate, convolute, 5-21 mm long, fused with the leaves for 2-12 mm, opaque, whitish, persistent. Peduncles 30-50(-70) mm long, 2-5 times as long as the fruiting spike, as thick as the stem. Spikes cylindrical, 5-20 mm long in fruit, contiguous to shortly distant. Flowers 4-7, with 4 carpels. Fruits extremely rare, 3.5-4.7(-6.2) mm long, dorsal keel distinct. Stem anatomy Stele of complex oblong type, sometimes of proto type, endodermis of 0-type, with varying strength, scattered interlacunarbundles present, subepidermal bundles present, pseudohypodermis present, 1-layered. Distribution North America. Note (1) P robbinsii is closely related to P maackianus. 37. Potamogeton maackianus A. BENNETT,J. Bot. 42: 74. 1904. ("Maackianus") [nom. cons. prop.] P serrulatusREGEL et MAACK in REGEL, MWm. Acad. Imp. Sci. Saint P6tersbourg, ser. 7, Sci. Phys.-Math.. 4(4): 139. 1861. = P robbinsii var.japonicus A. BENN.,Bull. Herb. Boissier 4: 549. 1896. Description Rhizome slender, terete, perennial, with wintergreen short shoots. Stem richly branched, slender, terete, annual to perennial; specialized dormant turions not developing. Submerged leaves sessile, linear, 14-80(-100) mm long, (1 .1-)1.5-4.0 mm wide, 8-25 times as long as wide, bright green to olive green or dark green, 3-5-veined, with 4-8 additional sclerenchymatous strands, with narrow rows of lacunae bordering the midrib, serrulate at margins, rounded at base, acute at apex. Floating leaves always absent. Stipules adnate, convolute, 4-12 mm 286 G. Wiegleb & Z. Kaplan long, fusedwith the leaves for 2-6 mm,translucentto opaque,persistent.Peduncles12-35 mm long, 1.5-5.5 times as long as the fruitingspike,as thickas the stem.Spikescylindrical,4-10 mm long in fruit,contiguous to shortlydistant.Flowers2-4, with 4 carpels.Fruitsrare,3.3-3.8 mm long, dorsalkeel distinct. Stem anatomy Stele of oblong type, endodermisof 0-type, interlacunarbundles absent, subepidermalbundles present, pseudohypodermis 1-layered. Distribution E andSE Asia. Hybrids 37 x 21. P. xphilippinensis A. BENN.,Philipp.J. Sci. 9: 342. 1914. [= P. maackianusx P wrightii] 25 x 37. P. xbiwaensis MIKI, Bot. Mag.(Tokyo)48: 326. 1934. [= P gramineusx P. maackianus] 37 x 26. P. xleptocephalus KOIDZ.in Y. Doi, Fl. Satsum. 2: 162. 1931. [= P maackianusx P perfoliatus] 37 x 46. P. xkyushuensis KADONO et WIEGLEB, J. Jap. Bot. 62(3): 76. 1987. [- P maackianusx P oxyphyllus] = P tenuinervisA. CAMUSin LECOMTE, Not. Syst. 1: 88. 1909, p. p. Notes (1) P. serrulatusREGEL et MAACK,the earliestnamerelatingto the speciesconcerned,has beenfoundnot to be illegitimateas formerlysupposed.However,for reasonsof preservingnomenclatural stabilityandin order to avoid a disadvantageous nomenclatural changeit is proposedto conservethe widely andpersistentlyused name,P maackianus(KAPLAN 1998). (2) Thetypecollectionof P tenuinervisconsistsof plantsof bothP.maackianusandP xkyushuensis. Selection of a single lectotypewill be necessaryin the future. 38. Potamogeton polygonus CHAMISSO et SCHLECHTENDAL, Linnaea 2(2): 184, t. 4, fig. 1 1. 1827. = ? P. pseudopolygonusHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 81. 1916. Description Rhizomefiliformto slender,terete,perennial.Stem richlybranched,filiformto slender,compressed,annual; axillaryor apical dormantturionsdeveloping.Submergedleaves sessile, linearto linear-lanceolate, 90-170 mm long, 3-6(-9) mm wide, 17-30 times as long as wide, brightgreen to dark green or olive green, (5-)7-9-veined, with 24-36 additionalsclerenchymatous strands,borderedby a very strongmarginalvein, with narrowrows of lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base, acuminateat apex. Floatingleaves always absent.Stipulesaxillary,convolute, 15-30 mm long, translucentto opaque, persistentbut erodingearly to fibrousstrandsat the apex. Peduncles15-55 mm long, 0.8-2.0 times as long as the fruitingspike, as thick as the stem. Spikescylindrical,12-23 mm long in fruit,contiguousto shortly distant.Flowers(6-)12-16, with 1-2 carpels.Fruits2.8-3.5 mm long, dorsalkeel distinct. Stem anatomy Stele of protoor reducedtrio type, endodermisof 0-type, scatteredinterlacunar bundlespresentor absent, subepidermal bundlespresent,pseudohypodermis present,1-layered. Distribution SouthAmerica. Hybrids 38 x 48. P xaftenuatus HAGSTR., Kungi. Svenska Vetenskapsakad. Handl. 55(5): 112. 1916. [= P polygonus x P pusillus] Note (1) P polygonusis superficiallysimilarto non-floatingleavedphenotypesof P ulei. However,they can be clearlydistinguishedby thepresenceof distinctsclerenichymatous strands,absenceof extensivelacunae,longer internodesand reducedcarpelnumber.The morphologicalsimilarityis due to convergenceamongdistinct speciesgroups(P epihydrus-group vs. P compressus-group). Taxonomy of Potamogeton 287 39. Potamogeton ochreatus RAOUL,Ann. Sci. Nat., Ser. 3, 2: 117. 1844. Description Rhizomeslender,terete,perennial,short.Stemrichlybranched,slender,terete,annual;lateraldormantturions developing.Submergedleaves sessile, linear,25-90(-130) mm long, 2-5(-6) mm wide, 10-25 timesas long as wide, brightgreen to darkgreen, sometimeswith a brownishtinge, (3-)5-veined, with 20-32 additional sclerenchymatous strands,borderedby a strongmarginalvein, with narrowrows of lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base, obtuseat apex. Floatingleaves always absent.Stipules axillary,convolute,4-15(-20) mm long, translucentto opaque,persistentbuterodingearlyto fibrousstrands at the apex. Peduncles(20-)30-75 mm long, 2-4 times as long as the fruitingspike, as thick as the stem. Spikescylindrical,9-15 mm long in fruit,contiguous.Flowers6-9, with4 carpels.Fruits2.8-4.5 mm long, dorsalkeel distinctto indistinct. Stem anatomy Stele of oblong type, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundlespresent, pseudohypodermis present,2-3-layered. Distribution SW, S, SE andE Australia,New Zealand. 40. Potamogeton furcatus HAGSTROM, Kungi. Svenska Vetenskapsakad. Handl. 55(5): 80. 1916. Description Rhizomefiliformto slender,terete,perennial,short.Stemrichlybranched,terete,slender,annual;specialized dormantturionsnot seen. Submergedleaves sessile, linear,85-140(-200) mm long, 2-4 mm wide, 25-50 timesas long as wide, brightgreento darkgreen,sometimeswitha brownishtinge,(3-)5-veined,with20-32 additionalscierenchymatous strands,borderedby a strongmarginalvein,withnarrowrowsof lacunaebordering the midrib,entireat margins,narrowlycuneateat base, acuteat apex.Floatingleaves alwaysabsent.Stipules axillary,convolute,8-15 mm long, translucentto opaque,persistentbuterodingearlyto fibrousstrandsat the apex. Peduncles 10-24 mm long, 1-3 times as long as the floweringspike, as thick as the stem. Spikes cylindrical,8-12 mm long in flower,contiguous.Flowers8, with4 carpels.Fruitsnot seen. Stem anatomy Stele of oblong type, endodermisof 0-type, interlacunarbundles absent, subepidermalbundles present, pseudohypodermis present,2-3-layered. Distribution Papua-NewGuinea,New Caledonia?,SE andE? Australia. Note (I) P furcatusis closely relatedto P ochreatus,buthas a differentgeographicaldistribution.It has also been informallydescribedas Potamogetonsp. A by LEACH& OSBORNE (1985). 41. Potamogeton acutifolius LINKin ROEMER et SCHULTES, Syst. Veg. ed. 16. 3: 513. 1818. P zosterifolius[var.]P. acutifolius(LINK)SCHULT. et SCHULT. f., Mant.3: 362. 1827. P compressussubsp.acutifolius(LINK)HOOK.f., Stud.Fl. Brit.Isl. 373. 1870. - P cuspidatusSCHRAD. ex MERT. et W.D.J.KOCH, RohlingsDeutschl.Fl. ed. 3. 1: 854. 1823, pro syn. -P acutifoliusvar.oc.majorFIEBER in BERCHT. et OPIZ,Oekon.-Techn.Fl. Bohm. 2(1): 272. 1838;FIEBER in BERCHT. et FIEBER, Potam.Bohmens35. 1838. - P. acutifoliusvar. minor FIEBER in BERCHT. et OPIZ,Oekon.-Techn.Fl. Bohm. 2(1): 272. 1838;FIEBER P. in BERCHT. et FIEBER, Potam.Bohmens35. 1838. - ? P henningiiA. BENN., J. Bot. 48: 151. 1910. ("Henningii") Description Rhizomeabsentor filiform,compressedto almostterete,annual,short.Stem sparinglyto richly branched, filiformto slender,stronglycompressedto flattened,0.4-3.0 mm wide, annual;axillaryor apicaldormant turions developing. Submergedleaves sessile, linear, 35-80(-135) mm long, 1.8-3.8(-5.5) mm wide, 13-30(-40) timesas long as wide, brightgreento darkgreen,sometimeswitha reddishtinge,3-veined,with 16-24 additionalsclerenchymatous strands,borderedby a strongmarginalvein, withnarrowrows of lacunae 288 G. Wiegleb & Z. Kaplan borderingthe midrib,entireat margins,narrowlycuneateat base, acuteto acuminateat apex.Floatingleaves always absent.Stipulesaxillary,convolute,1O-21(-29) mm long, translucentto opaque,persistentbut soon erodingto fibrousstrandsat the apex.Peduncles3-15(-26) mm long, 1-6 times as long as the fruitingspike, as thick as the stem. Spikes almostglobose, 4-8 mm long in fruit,contiguous.Flowers4-7, with 1 carpel. Fruits3.0-4.0(-4.7) mm long, dorsalkeel distinct. Stem anatomy Stele of oblong type, endodermisof 0-type, interlacunarbundles absent, subepidermalbundles present, multicellular, pseudohypodermis absent. Distribution Temperateregionsof Europe,W Asia? Hybrids 41 x 47. P. xpseudofriesii DANDYet G. TAYLOR, Kew Bull. 12: 332. 1957. [= P acutifoliusx P.friesii] 41 x 48. P. xsudermanicus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 73. 1916. [= P acutifoliusx P pusillus] Notes (1) P acutifoliusis a species closely relatedto P compressus. Even thoughnot alwayseasily recognizablein its non-floweringstate,it is distinguishedin manycharactersof its inflorescenceandflower/fruitmorphology. UnlikeP compressus,it occupiesa limitedgeographicalarea. (2) P henningiiA. BENN.hasbeenrecentlyreportedfromseveralplacesin Siberia(VOLOBAEV1993).However, the present-dayconceptis unlikelyto correspondto the originalone. Biosystematicalrevisionof the whole groupis desirable. (3) Theoccurrenceof the hybridP acutifoliusx P compressushasrepeatedlybeenclaimedto arise.However, bothparentsareoftenindistinguishable vegetativelyowingto significantoverlapof characters.Therefore,their hybridcannotbe identifiedon the basis of non-floweringspecimens.Experimentalcrossingis necessaryto confirmthe existenceof the hybrid. 42. Potamogeton compressus Linnaeus, Sp. Pi. 127. 1753. ("compressum") = P zosterifolius SCHUMACH., Enum.P1. 1: 50. 1801. ("zosterefolium") = P zosterophyllus DUMORT.,Fl. Belg. 164. 1827, nom. illeg. = Spirilluszosterifolius(SCHUMACH.) NIEUWL.,Amer.Midl.Naturalist3: 17. 1913. = P complanatusWILLD.,Ges. Naturf.FreundeBerlinMag. NeuestenEntdeck.GesammtenNaturk.3: 297. 1809. ("complanatum") = P laticaulisWAHLENB.,Fl. Suec. 1: 107. 1824. ("laticaule') = P carinatus KUPFFERin MUHLEN,Korrespondensbl. Naturf.-Vereins Riga 49: 164. 1906. _ P acutifolius subsp. carinatus (KUPFFER)GRAEBN.in ENGL.,Pflanzenr. 31 (IV.11): 104. 1907. = P monoginus MIKI,Water Phan. Japan 18. 1937. Description Rhizome absent or filiform, compressed, annual, usually short. Stem richly branched, filiform to slender, strongly flattened, 0.5-3.4(-4.8) mm wide, annual; axillary or apical dormant turions developing. Submerged leaves sessile, linear, (70-)85-240(-290) mm long, (2.2-)2.9-5.4(-6.0) mm wide, 20-60(-90) times as long as wide, olive green to dark green, sometimes with a reddish tinge, (3-)5-veined, with 20-32 additional sclerenchymatous strands, bordered by a strong marginal vein, with narrow rows of lacunae bordering the midrib, entire at margins, narrowly cuneate at base, acute to mucronate at apex. Floating leaves always absent. Stipules axillary, convolute, (19-)22-35(-55) mm long, translucent to opaque, persistent but eroding early to fibrous strands at the apex. Peduncles (21-)28-69(-95) mm long, 2-5 times as long as the fruiting spike, as thick as the stem. Spikes cylindrical, 16-33 mm long in fruit, contiguous. Flowers 10-20, with (1-)2(-3) carpels. Fruits 3.4-4.0 mm long, dorsal keel distinct. Stem anatomy Stele of oblong type, endodermis of 0-type, interlacunar bundles absent, subepidermal bundles present, multicellular, pseudohypodermis absent. Taxonomy of Potamogeton 289 Distribution Borealand temperateregionsof EuropeandAsia. Hybrids 42 x 46. P. xfauriei (A. BENN.)MIKI,Water Phan. Japan 45. 1937. ("Fauriei") [= P compressus x P oxyphyllus] _ P oxyphyllus var.fauriei A. BENN.,J. Bot. 42: 76. 1904. ("Fauriei") 43. Potamogeton zosteriformis FERNALD,Mem. Amer. Acad. Arts Sci. 17: 36. 1932. P. zosterifolius subsp. zosteriformis (FERNALD)HULTEN,Kungl. Svenska Vetenskapsakad. Handl., ser. 4, 8(5) [Circump.P1. 1]: 168. 1964. = P zosterifolius var.minor HOOK.,Fl. Bor.-Amer.2: 172. 1838. = P zosterifoliusvar.americanusA. BENN.,Trans.& Proc.Bot. Soc. Edinburgh29(1):46. 1924. Description Rhizomeabsentor filiformto slender,compressed,annual.Stemrichlybranched,filiformto slender,flattened, 0.6-3.2 mm wide, annual;axillaryor apicaldormantturionsdeveloping.Submergedleaves sessile, linear, 50-200 mmlong,(1.8-)2.3-5.0 mmwide,25-50 timesas longas wide,brightgreento darkgreen,sometimes witha reddishtinge,3-veined,with20-34 additionalsclerenchymatous strands,borderedby a strongmarginal vein, with narrowrows of lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base, acuteto mucronateat apex. Floatingleaves always absent.Stipulesaxillary,convolute,(16-)20-32(-40) mm long, translucent, persistent,generallyintactthroughout the season.Peduncles(19-)30-100 mm long, 1.5-5.0 times as long as the fruitingspike, as thick as the stem. Spikescylindrical,15-32 mm long in fruit,contiguous. Flowers10-20, with (1-)2 carpels.Fruits4.0-5.0(-5.5) mm long, dorsalkeel distinct. Stem anatomy Stele of oblong type, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundlespresent, pseudohypodermis absent. Distribution NorthAmerica. Hybrids 51 x 43. P. xhaynesii HELLQ.et G.E. CROW,Brittonia 38(4): 415. 1986. [= P. strictifolius x P zosteriformis] 53 x 43. P. xogdenii HELLO. et R.L. HILTON, Syst. Bot. 8(1): 88. 1983, pro sp. [= P. hillii x P. zosteriformis] Notes (1) P zosteriformisis closely relatedto P compressus.They are vicariantin theirdistribution.The former occursin NorthAmericawhile the latteris Eurasian. (2) P ogdeniiwas describedas a speciesof hybridogenous origin.The speciesnaturewasjustifiedespecially by the rich fruit production. However, especially P xangustifolius, but also P xfluitans and P xsudermanicus, arealso knownto producefruits.Nothingis known,however,aboutthe viabilityandgerminationrateof these fruits.Even thoughP xogdeniiis clearlyintermediate betweenthe putativeparents,its speciesstatusmay be substantiated in futurestudies. 44. Potamogeton manchuriensis (A. BENNETT)A. BENNETT,Trans. & Proc. Bot. Soc. Edinburgh 29: 50. 1924. ("mandschuriensis") P acutifolius subsp.manchuriensis A. BENN.,J. Bot. 42: 76. 1904. - P manchuriensis (A. BENN.)FERNALD,Mem. Amer. Acad. Arts Sci. 17: 68. 1932. [isonymum] Description Rhizome filiform, slightly compressed,perenniail.Stem sparinglyto richly branched,filiform, slightly compressed,annual;axillaryor apicaldormanlt tlrions developing.Submergedleaves sessile, linear,40-150 mm long, 1.5-2.5 mm wide, 25-60 times as long as wide, olive green to darkgreen,3-veined,with 10-18 additionalsclerenchymatous strands,borderedby a strongmarginalvein,withnarrowrowsof lacunaebordering the midrib,entireat margins,narrowlycuneateat base, acuminateat apex. Floatingleaves always absent. 290 G. Wiegleb & Z. Kaplan Stipulesaxillary,convolute, 18-30 mm long, translucentto opaque,persistentbut erodingearly to fibrous strandsat the apex.Peduncles20-55 mmlong, 2.5-3.5 timesas long as the fruitingspike,as thickas the stem. Spikescylindrical,6-17 mm long in fruit,contiguous.Flowerandcarpelnumbersunknown.Fruits2.8-3.5 mm long, dorsalkeel distinct. Stem anatomy Stele of oblong type, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundles present, pseudohypodermis absent. Distribution NE Asia. Note (1) P manchuriensisis insufficientlyknown.At presentit is regardedas being relatedto P. compressus. 45. Potamogeton sibiricus A. BENNETT, J. Bot. 28: 300. 1890. = P subsibiricusHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 84. 1916. = P porsildiorusFERNALD,Mem. Amer.Acad. ArtsSci. 17:40. 1932. ("Porsildiorum") = P anadyrensisV.N. VASSIL.,Bot. Mat. Gerb.Bot. Inst. Akad.Nauk SSSR [= Not. Syst. Herb.Inst.Bot. Acad. Sci. URSS] 17:45. 1955. Description Rhizomefiliform,slightlycompressed,perennial.Stem unbranchedor sparinglybranched,filiform,slightly compressed,annual;axillaryorapicaldormantturionsdeveloping.Submergedleavessessile,linear,35-80(-95) mm long, 1.2-2.0(-2.5) mm wide, 20-40 times as long as wide, olive greento darkgreen, 3-veined,with (8-)12-20 additionalsclerenchymatousstrands,borderedby a strongmarginalvein, with narrowrows of lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base, acuteto roundedor mucronateat apex.Floatingleaves alwaysabsent.Stipulesaxillary,convolute,(10-)15-25 mm long, translucentto opaque, persistentbuterodingearlyto fibrousstrandsat the apex.Peduncles17-35(-50) mm long, 1-3 timesas long as the fruitingspike,as thick as the stem. Spikescylindrical,7-17 mm long in fruit,contiguous.Flowerand carpelnumbersunknown.Fruits2.1-3.0 mm long, dorsalkeel distinct. Stem anatomy Stele of oblong type, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundlespresent, pseudohypodermis absent. Distribution NE Europe,N Asia, NW andN NorthAmerica. Note (1) P sibiricusis insufficientlyknown.Most probablyit is relatedto P oxyphyllusor P compressus. 46. Potamogeton oxyphyllus MIQUEL, Ann. Mus. Bot. Lugduno-Batavum 3: 161. 1867. = ? P chongyangensisW.X.WANG,Acta Phytotax.Sin. 22(6): 490. 1984. Description Rhizome filiform, terete, perennial,continouslygrowing. Stem richly branched,filiform, terete, mostly wintergreen; axillarydormantturionsdeveloping.Submergedleavessessile,linearto narrowlylinear-lanceolate, 50-105(-135) mm long, 2.0-3.5(-4.2) mm wide, 20-40 times as long as wide, brightgreen to darkgreen, 5-7(-9)-veined, with (2-)8-16(-20) faintadditionalsclerenchymatous strands,borderedby a strongmarginal vein, withnarrowrows of lacunaeborderingthemidrib,entireat margins,narrowlycuneateat base,acuminate at apex. Floatingleaves always absent.Stipulesaxillary,convolute,15-25 mm long, translucent,persistent. Inflorescenceaxillary.Peduncles20-45 mmlong, 2-3 timesas long as the fruitingspike,as thickas the stem. Spikescylindrical,6-15 mm long in fruit,contiguous.Flowers5-9, with 4 carpels.Fruits3.2-3.8 mm long, dorsalkeel indistinct. Stem anatomy Stele of oblong type, endodermisof 0-type, interlacunarbundles absent, subepidermalbundles present, pseudohypodermis absent. Taxonomy of Potamogeton 291 Distribution E andSE Asia. Hybrids 37 x 46. P. xkyushuensis KADONO et WIEGLEB, J. Jap. Bot. 62(3): 76. 1987. [= P maackianus x P oxyphyllus] 42 x 46. P. xfauriei (A. BENN.)MIKI,Water Phan. Japan 45. 1937. ("Fauriei") [= P compressus x P. oxyphyllus] 46 x 48. P. xorientalis HAGSTR., Bot. Not. 1908: 102. 1908, pro sp. [= P oxyphyllus x P. pusillus] - P henryiFERNALD, Mem. Amer.Acad.ArtsSci. 17: 73. 1932. ("Henryi") 56 x 46. P. xkamogawaensis MIKI,Bot. Mag. (Tokyo) 48: 328. 1934. [= P. octandrus x P. oxyphyllus] Note (1) P xorientalisis a widespreadhybridoccurringalmostthroughout theareaof P oxyphyllus.Despiteits vital andabundantgrowthit is completelysterile. 47. Potamogeton friesii RUPRECHT,Beitr. Pflanzenk. Russ. Reiches 4: 43. 1845. ("Friesii") P pusillus subsp. friesii (RUPR.)HOOK.f., Stud.Fl. Brit.Isl. ed. 3. 435. 1884. ("Friesii") Spirillusfriesii(RUPR.)NIEUWL., Amer.Midl.Naturalist3: 17. 1913. -P mucronatusSCHRAD. ex ROEM. et SCHULT., Syst. Veg.ed. 16. 3: 517. 1818,nom. nud. = P compressus var. ,B.acutus SCHLTDL., Fl. Berol. 1: 117. 1823. = P compressus [var.] P. elongatus WAHLENB.,Fl. Suec. 1: 107. 1824. ("elongatum") - P pusillus[var.]("spielart") a. latifoliusG. MY., ChlorisHan.525. 1836,nom. illeg. = P pusillus[var.]a. majorFR.,Novit.Fl. Suec.ed. 2. 48. 1828,nom.illeg., nonMERT. et W.D.J.KOCH1823. P =P =P - P major [FR.] MORONG,Mem. Torrey Bot. Club 3(2): 41. 1893. [non vidimus] mucronatus SCHRAD.ex RCHB.,Icon. Fl. Germ. Helv. 7: 15. t. 24. 1845, pro syn. oederi G. MEY.,Fl. Hanov. Exscurs. 536. 1849. ("Oederi") mucronatus SCHRAD.ex SONDER,Fl. Hamburg. 99. 1850. ("1851") P pusillusvar.mucronatus(SCHRAD. ex SONDER) HOOK. f., Stud.Fl. Brit.Isl. 374. 1870. P pusillus[subsp.]b) mucronatus(SCHRAD. ex SONDER) CELAK., Analyt.Kvet.Cech,Mor.a Rak.Slezska ed. 3. 44. 1897. - P compressus var. dimidius CREP.,Notes P1. Rar. Belgique 4: 44. 1864. Description Rhizomeabsentor present,filiform,compressed,annual,short.Stem richlybranched,filiform,compressed, annual;axillaryor apicaldormantturionsdeveloping.Submergedleavessessile,linear,(31-)40-85(-100) mm long, 1.5-3.5(-4.0) mm wide, 15-45 times as long as wide, brightgreen, sometimeswith a reddishtinge, (3-)5(-7)-veined, withoutadditionalsclerenchymatous strands,borderedby a faintmarginalvein, withnarrow rowsof lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base,mucronateat apex.Floating leaves alwaysabsent.Stipulesaxillary,shortlyconnateonly at base andsplitintotwo remnantsat apex,7-25 mm long,opaque,whitish,persistent.Peduncles15-40(-70) mmlong, 1-5 timesas long as the fruitingspike, as thickas the stem. Spikes cylindrical,7-14 mm long in fruit,contiguousto shortlydistant.Flowers4-8, with 4 carpels.Fruits2.4-3.0 mm long, dorsalkeel indistinct. Stem anatomy Stele of circulartype, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundlespresent, pseudohypodermis absent. Distribution borealandtemperateregionsthroughoutthe northernhemisphere. Circumpolar, Hybrids 35 x 47. P. xlintonii FRYER,J. Bot. 38: 366. 1900; FRYER,Bot. Exch. Club Brit. Isles Rep. 1899-1900: 21. 1900. ("Lintoni") [= P crispus x P friesii] 292 G. Wiegleb & Z. Kaplan 41 x 47. P. xpseudofriesii DANDY et G. TAYLOR, Kew Bull. 12: 332. 1957. [= P acutifolius x P friesii] pusillus LINNAEUS,Sp. Pi. 127. 1753. - P pusillus [subsp.] a) genuinus CELAK.,Analyt. Kvet. Cech, Mor. a Rak. Slezska ed. 3. 43. 1897, nom. inval. Spirillus pusillus (L.) NIEUwL.,Amer. Midl. Naturalist 3: 18. 1913. = P pusillus [var.] a. major MERT.et W.D.J. KOCH,Rohlings Deutschl. Fl. ed. 3. 1: 857. 1823. = P pusillus var. P. tenuissimus MERT.et W.D.J. KOCH,R6hlings Deutschl. Fl. ed. 3. 1: 857. 1823. = P pusillus [subsp.] P. tenuissimus (MERT.et W.D.J. KOCH)SCHUBL.et G. MARTENS,Fl. Wurttemb. 112. 1834. P. tenuissimus (MERT.et W.D.J. KoCH) RCHB.,Icon. Fl. Germ. Helv. 7: 14, t. 22, fig. 39. 1845. - P pusillus subsp. tenuissimus (MERT.et W.D.J. KOCH)R.R. HAYNESet HELLQ.,Novon 6(4): 370. 1996. [isonymum] = ? P. denticulatus LINKin BUCH,Phys. Beschr. Canar. Ins. 138. 1825. = P. gracilis FR., Novit. Fl. Suec. ed. 2. 50. 1828, nom. illeg., non WOLFG.1827. P noltei A. BENN.,J. Bot. 28: 300. 1890. ("Noltei") = P panormitanus BIv. in A. BIv. f., Nuove Piante 6. 1838. P pusillus var. panormitanus (Biv.) A. BENN.,J. Bot. 19: 242. 1881. P pusillus subsp. panormitanus (BIv.) G. FISCH.in DORFLER, Herb. Norm. no. 4767. 1905. P pusillus proles panonnitanus (BIV.) GRAEBN.in ENGL.,Pflanzenr. 31 (IV.11): 116. 1907. = P panormitanus var. minor BIv. in A. BIv. f., Nuove Piante 6. 1838. = P berchtoldii FIEBERin BERCHT.et OPIZ,Oekon.Techn. Fl. Bohm. 2(1): 277. 1838; FIEBERin BERCHT.et FIEBER,Potam. Bohmens 40. 1838. ("Berchtoldi") P pusillus subsp. berchtoldii (FIEBER)MAGNIN,Bull. Soc. Bot. France 43: 446. 1896. ("Berchtoldi") P pusillus var. berchtoldii (FIEBER)ASCH.et GRAEBN.,Synops. Mitteleur. Fl. 1: 345. 1897. P pusillus proles berchtoldii (FIEBER)GRAEBN.in ENGL.,Pflanzenr. 31 (IV.I 1): 15. 1907. ("Berchtoldii") = P. berchtoldii [var.] a. mucronatus FIEBERin BERCHT.et OPIZ,Oekon.-Techn. Fl. Bohm. 2(1): 277. 1838; FIEBERin BERCHT.et FIEBER,Potam. Bohmens 40. 1838. = P berchtoldii [var.] P. acuminatus FIEBERin BERCHT.et OPIZ,Oekon.-Techn. Fl. Bohm. 2(1): 278. 1838; FIEBERin BERCHT.et FIEBER,Potam. Bohmens 41. 1838. = P grisebachii HEUFF.,Verh. K. K. Zool.-Bot. Ges. Wien 8: 200. 1858. ("Grisebachii") = ? P. berteroanus PHIL.,Linnaea 30: 200. 1859-1860. ("Berteroanus") = P subtrichoides SCHUR,Enum. P1. Transsilv. 633. 1866. = P pusillus var. gemmiparus J.W. ROBBINSin A. GRAY,Manual Bot. North. U. S. ed. 5. 489. 1867. - P gemmiparus J.W. ROBBINSin A. GRAY,Manual Bot. North. U. S. ed. 5. 489. 1867, pro syn. P gemmiparus (J.W. ROBBINS)MORONG,Bot. Gaz. (Crawfordsville) 5: 51. 1880. P pusillus subsp. gemmiparus (J.W. ROBBINS)R.R. HAYNESet HELLQ., Novon 6(4): 370. 1996. = P tenuifolius F PHIL.,Anal. Mus. Nac. Chile 2(8): corr. pag. 95. 1891, nom. illeg., non RAF. 1811. _ P aschersonii A. BENN.,J. Bot. 31: 294. 1893. ("Aschersonii") = P trinervius G. FISCH.,Ber. Bayer. Bot. Ges. 11: 29 et 123. 1907, pro hybr. P pusillus (sub P panormitanus) x P trichoides. = ? P uruguayensis A. BENN.et GRAEBN.in ENGL.,Pflanzenr. 31 (IV.l 1): 1 11. 1907. = P pusillus subsp. argentinus A. BENN.,J. Bot. 46: 250. 1908. = P turionifer HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 91. 1916, pro hybr. P foliosus x P pusillus. = ? P pusilliformis HAGSTR.,Kungl. Svenska Vetenskapsakad.Handl. 55(5): 97. 1916, pro hybr. P.friesii (sub P mucronatus) x P pusillus. = P dualis HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 103. 1916, pro hybr. P panormitanus x P pusillus. = P badius HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 104. 1916. = ? P antaicus HAGSTR.,Kungl. Svenska Veteniskapsakad.Handl. 55(5): 105. 1916. = P exiguus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 106. 1916. = P lacunatus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 120, fig. 53. 1916. 48. Potamogeton Taxonomy of Potamogeton = ? P loculosus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 120. 1916. = ? P. groenlandicus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 127. 1916. _ ? P pusillus subsp. groenlandicus (HAGSTR.)BOCHER,Meddel. Groenland 147(9): 44. 293 1952. = P subjavanicus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 129. 1916. = P pusillus subsp. lacustris PEARSALL et PEARSALLf., J. Bot. 59: 163. 1921. _ P lacustris (PEARSALL et PEARSALL f.) DRUCE,List Brit. P1. ed. 2. 117. 1928. = ? P tubulatus HAGSTR.in HEDIN,Southern Tibet 6(3): 96. 1922. = P clystocarpus FERNALD,Mem. Amer. Acad. Arts Sci. 17: 79. 1932. = P hoggarensis DANDY,J. Linn. Soc., Bot. 50: 522. 1937. = P millardii HESL.HARR., Proc. Univ. Durham Phil. Soc. 10: 365. 1942. = P skvortsovii KLINKOVA, Byull. Glavn. Bot. Sada 1993(168): 48. 1993. Description Rhizome absent or present later in the growing season, filiform, terete, annual to biennial. Stem sparingly to richly branched, filiform, terete to slightly compressed, annual to perennial; axillary or apical dormant turions developing, rarely directly on rhizomes, or sometimes not developing. Submerged leaves sessile, linear, (15-)20-85(-110) mm long, (0.3-)0.8-2.5(-3.1) mm wide, (15-)20-60(-90) times as long as wide, bright green to olive green or dark green, sometimes with a brownish tinge, (1-)3(-5)-veined, without additional sclerenchymatous strands, mostly bordered by a faint marginal vein, with or without narrow or sometimes broad rows of lacunae bordering the midrib, entire at margins, narrowly cuneate at base, acuminate or acute to subobtuse at apex. True floating leaves absent but rarely the uppermost leaves with lamina floating at the water surface, subsessile, linear-oblanceolate, 18-38 mm long, 1.3-3.5 mm wide, 7-20 times as long as wide, translucent, membranous to almost subcoriaceous, bright green, 3-5-veined, with broad rows of lacunae bordering the midrib, narrowly cuneate at base, acute to narrowly obtuse at apex. Stipules axillary, convolute or connate, 4-18(-32) mm long, translucent, persistent to decaying. Peduncles (6-)10-45(-80) mm long, 1-6 times as long as the fruiting spike, as thick as the stem. Spikes cylindrical, 4-13 mm long in fruit, contiguous to shortly distant. Flowers 2-7, with (3-)4(-7) carpels. Fruits 1.8-2.7(-3.3) mm long, dorsal keel indistinct. Stem anatomy Stele of circular type, rarely of oblong type, endodermis of 0-type, interlacunarbundles absent, subepidermal bundles present, pseudohypodermis absent or partly 1-layered. Distribution Europe, Africa, Asia, North America and South America. Hybrids 1 x 48. P. xrivularis GILLOT in MAGNIER, Scrin. Fl. Select. 6: 118. 1887. [= P polygonifolius x P pusillus] 3 x 48. P. xianceolatus SM. in SOWERBY, ENGL.Bot. 28: t. 1985. 1809, pro sp. ("lanceolatum") [= P coloratus x P pusillus] 25 x 48. P. xvariifolius THORE,Essai Chloris 47. 1803, pro sp. ("variifolius") [= P natans x P pusillus] 26 x 48. P. xmysticus MORONG, Bot. Gaz. (Crawfordsville) 5: 50. 1880, pro sp. [= P. perfoliatus x P pusillus] 38 x 48. P. xattenuatus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 112. 1916. [= P. polygonus x P pusillus] 41 x 48. P. xsudermanicus HAGSTR.,Kungi. Svenska Vetenskapsakad. Handl. 55(5): 73. 1916. [= P acutifolius x P. pusillus] 46 x 48. P. xorientalis HAGSTR., Bot. Not. 1908: 102. 1908, pro sp. [= P. oxyphyllus x P pusillus] 48 x 55. P. xgrovesii DANDY et G. TAYLOR, Watsonia6: 316. 1967. [= P. pusillus x P. trichoides] 56 x 48. P. xapertus MIKI,Bot. Mag. (Tokyo) 49: 690. 1935. [= P octandrus x P pusillus] 294 G. Wiegleb & Z. Kaplan Notes (1) P.pusillusis regardedhereas a highlypolymorphicspecieswithnumerousregionalformsandecomorphoses. Moredetailedclassificationseems to be impossiblebecauseof the highlyreticularvariation.No correlatedset of characterswhich wouldmakediscrimination of taxapossiblehavebeen confirmed. (2) The SouthAmericanP. pusillushas been oftentreatedas a separatespecies,viz P. berteroanus.However, these plantsfall well withinthe variationpatternof P. pusillusas definedhere. (3) ManyauthorsregardP. berchtoldiiand/orP gemmiparusas a separatespecies of the respectiveregions wherethey occur.TheirdistinctionfromP. pusilluss. str.is, however,insufficient. (4) Some of the plantscalled P. groenlandicusshow certaincharactersdeviantfromthe presentconceptof P pusillus.They are characterizedespeciallyby the leaves with up to 8 additionalsclerenchymatous strands. Theseplantsareknownonly froma geographicallylimitedareain WesternGreenland.Furtherresearch,such as experimentalcultivation,is necessaryin orderto clarifytheirstatus. (5) P clystocarpus and P hoggarensis are regarded as extreme local morphotypes of P pusillus. Both are knownonly fromthe type locality. (6) ManyhybridsbetweenspecieswithintheP pusillus-grouphavebeenproposed.Linear-leavedspecieshave a reducedmorphologicalvariationandarephenotypically extremelyvariableandplastic.Distinguishinghybrids on a solely morphologicalbasis is generallyavoided.Consequentlymanyproposednamesof allegedhybrids cannotbe acceptedon the basisof ourpresentstateof knowledge.Crossingexperimentsarenecessaryto solve this problem. 49. Potamogeton gayiA. BENNETT, Ann. K. K. Naturhist. Hofmus. Wien 7(4): 293. 1892. ("Gayii") = P burkartiiHORNex TURin CABRERAet al., Fl. Prov.BuenosAires 4(1): 287. 1968. Description Rhizomefiliformto slender,terete,perennial,long, regularlyproduced.Stem sparinglyto richlybranched, filiform,tereteto slightlycompressed,perennial;axillarydormantturionssometimesdeveloping.Submerged leaves sessile, linear,55-100 mm long, (2-)3-6 mm wide, 18-25 timesas long as wide, brightgreento dark green,oftenwitha reddishorbrownishtinge,3-5-veined,withoutadditionalsclerenchymatous strands,bordered by a strongmarginalvein, with narrowrows of lacunaeborderingthe midrib,entireat margins,narrowly cuneateat base, acute at apex. Floatingleaves always absent.Stipulesaxillary,convolute,14-20 mm long, translucent,persistentto decaying.Peduncles15-60 mm long, 1.5-4.5 times as long as the fruitingspike,as thickas the stem.Spikescylindrical,10-17 mm long in fruit,contiguous.Flowers5-12, with4 carpels.Fruits 4.3-4.6 mm long, dorsalkeel distinct. Stem anatomy Steleof oblongtype,endodermisof 0 type,interlacunar bundlesabsentor rarelypresent,subepidermal bundles present,multicellular,pseudohypodermis 1(-2)-layered. Distribution SouthAmerica. Note (1) P gayi is closely relatedto P.pusillus.However,it deviatesfromthe variationpatternof the latterspecies and it is confinedto a restrictedgeographicalarea. 50. Potamogeton rutilus WOLFGANG in SCHULTES et SCHULTES f., Mant. 3: 362. 1827. P pusillusvar.rutilus(WOLFG.)WIEDEM.et E. WEBER,Beschr.Phan.Gew.Esth-,Liv-Curl.94. 1852. - P cespitosusNOLTEex RCHB.,Icon. Fl. Germ.Helv.7: 15, t. 23, fig. 41. 1845, pro syn. ("cespitosum") Description Rhizomeabsentor filiform, slightly compressed,annual.Stem unbranchedor sparinglybranched,filiform, slightlycompressed,annual;axillarydormantturionsdeveloping.Submergedleavessessile, linear,32-75 mm long,0.5-1.1 mmwide, 35-80 timesas long as wide,brightgreen,sometimeswitha brownishtinge,somewhat rigid,3-veined,withoutadditionalsclerenchymatous strands,borderedby a strongmarginalvein,withoutrows of lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base,acuminateat apex.Floatingleaves alwaysabsent.Stipulesaxillary,shortlyconnate,15-20 mmlong,opaque,fibrous,whitish,persistent.Peduncles (3-)10-17 mmlong, 1-3 timesas long as the fruitingspike,as thickas the stem.Spikescylindrical,4-10 mm long in fruit,contiguous.Flowers5-6, with (2-)4 carpels.Fruits2.0-2.1 mm long, dorsalkeel indistinct. Taxonomy of Potamogeton 295 Stem anatomy Stele of circulartype, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundlespresent, pseudohypodermis absent. Distribution W, N andC Europe,W Asia. Note (1) P rutilusis relatedto P. pusillus. It comprisesplants with a special set of charactersof a restricted geographicalarea. 51. Potamogeton strictifolius A. BENNETT, J. Bot. 40: 148. 1902. P pusillusvar.pseudorutilusA. BENN.,J. Bot. 39: 201. 1901. ("pseudo-rutilus") - P strictifolius var. typicus FERNALD, Mem. Amer. Acad. Arts Sci. 17: 56. 1932, nom. inval. = P strictifolius var. rutiloides FERNALD,Mem. Amer. Acad. Arts Sci. 17: 57. 1932. = P pusillusvar.rutiloides(FERNALD) B. BOIVIN, NaturalisteCanad.94: 527. 1967. = P longiligulatus FERNALD,Mem. Amer. Acad. Arts Sci. 17: 66. 1932. Description Rhizomefiliform,terete,annual,short.Stem unbranchedor branched,filiform,slightlycompressed,annual; axillaryor apicaldormantturionsdeveloping.Submergedleaves sessile, linear,12-63 mm long, 0.6-2.0 mm wide, 20-40 times as long as wide, bright green, sometimes with a brownishtinge, somewhatrigid, 3-5(-7)-veined, withoutadditionalsclerenchymatous strands,borderedby a strongmarginalvein, without rows of lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base,acuteto acuminateat apex. Floatingleaves alwaysabsent.Stipulesaxillary,connate,6-16 mm long, opaque,fibrous,whitish,persistent. Peduncles10-45 mm long, 1.5-3.5 timesas long as the fruitingspike,as thickas the stem,slightlythickened upwards.Spikescylindrical,6-13 mm long in fruit,contiguous.Flowers5-7, with 4 carpels.Fruits1.9-2.1 mm long, dorsalkeel indistinct. Stem anatomy Stele of circulartype, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundlespresent, pseudohypodermis absent. Distribution NW,C and E NorthAmerica. Hybrids 51 x 43. P. xhaynesii HELLQ.et G. E. CROW, Brittonia38(4):415. 1986. [= P strictifoliusx P zosteriformis] Note (1) P strictifoliusis closely relatedto P rutilus.It is distinguishedmainlyon quantitativecharacters. 52. Potamogeton foliosus RAFINESQUE, Med. Repos., Hexade 3, 2: 409. 1811. ("foliorum") - P foliosus RAF.,Med. Repos.,Hexade2, 5: 354. 1808, nom. prov.("foliosum") = P pauciflorusPURSH,Fl. Amer.Sept. 1: 121. 1814,nom. illeg. ("pauciflorum") = Spirillusfoliosus (RAF.) NIEUWL.,Amer. Midl. Naturalist 3: 18. 1913. P foliosus var.genuinusFERNALD,Mem.Amer.Acad.ArtsSci. 17: 43. 1932, nom. inval. = P niagarensisTUCK.,Amer.J. Sci. Arts,ser.2, 7: 354. 1849. = P pauciflorusvar.niagarensis(TUCK.)J.W. ROBBINSin A. GRAY,ManualBot. North.U. S. ed. 2. 435. 1856. = P foliosus var.niagarensis(TUCK.)MORONG,Mem.TorreyBot. Club3(2): 39. 1893. - = Spirillusfoliosusvar.niagarensis(TUCK.) NIEUWL., Amer.Midl.Naturalist3: 18. 1913. = P pauciflorusvar.californicusMORONG, Bot. Gaz. (Crawfordsville)10: 254. 1885. = P foliosus var.californicus(MORONG) MORONG. Mem.TorreyBot. Club3(2): 40. 1893. = P californicus(MORONG) PIPER, CoItr. Uitjl. St. N;at.Herb.IlI:98. 1906. = P curtisiiMORONG,Bull. TorreyBot. Clutb 13: 145. 1886.("Curtsii") = P.foliosus var. macellusFERNALD, Mein.Amer.Acad.ArtsSci. 17: 46. 1932. = P fibrillosusFERNALD, Mem. Amer.Acad.ArtsSci. 17:51. 1932. 296 G. Wiegleb & Z. Kaplan P foliosus var.fibrillosus(FERNALD)R.R. HAYNESet REVEAL,Rhodora75: 76. 1973. P foliosus subsp.fibrillosus(FERNALD)R.R. HAYNESet HELLQ.,Novon 6(4): 370. 1996. Description Rhizomefiliform,slightlycompressed,perennial.Stembranched,filiform,slightlycompressed,annual;axillary or apicaldormantturionsdeveloping.Submergedleaves sessile, linear,13-82 mm long, 0.3-2.3 mm wide, 30-60 times as long as wide, brightgreento olive green,sometimeswith a reddishtinge, (1-)3(-5)-veined, withoutadditionalsclerenchymatous strands,borderedby a faintmarginalvein, with or withoutnarrowrows of lacunaeborderingthe midrib,entire at margins,narrowlycuneateat base, narrowlyobtuse or acute to acuminateat apex. Floatingleaves always absent.Stipulesaxillary,convoluteor connate,2-22 mm long, translucentto opaque,persistentto decaying.Peduncles3-1 1(-37) mm long, 2-7 timesas long as the fruiting spike, as thickas the stem, slightlythickenedupwards.Spikesglobose to cylindrical,2-7 mm long in fruit, contiguous.Flowers2-4, with4 carpels.Fruits1.4-2.7 mm long, dorsalkeel distinct,undulate,dentate,to 0.4 mm high. Stem anatomy Stele of circulartype, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundlespresent, pseudohypodermis absent. Distribution NorthandCentralAmerica. Note (1) P foliosus is relatedto P pusillus.It is distinguishedmainlyon the basisof inflorescence,flowerandfruit characters. 53. Potamogeton hiliii MORONG, Bot. Gaz. (Crawfordsville) 6: 290. 1881. ("HiIIii") = P porteri FERNALD,Mem. Amer.Acad.ArtsSci. 17: 73. 1932.("Porteri") Description Rhizome absent or present, filiform, slightly compressed,perennial.Stem branched,filiform, slightly compressed,annual;apical dormantturionsdeveloping.Submergedleaves sessile, linear,20-60 mm long, 0.6-2.5(-4.0) mm wide, 20-40 timesas long as wide,brightgreento olive green,3-veined,withoutadditional sclerenchymatous strands,borderedby a faintmarginalvein,withnarrowrowsof lacunaeborderingthemidrib, entireat margins,narrowlycuneateat base,acuminateat apex.Floatingleavesalwaysabsent.Stipulesaxillary, convolute,7-16 mm long, translucent,persistent.Peduncles6-14 mm long, 1.5-3.0 times as long as the fruitingspike, as thick as the stem. Spikes globose, 2-7 mm long in fruit,contiguous.Flowers2-4, with 4 carpels.Fruits2.3-4.0 mm long, dorsalkeel distinct,dentate,to 0.2 mm high. Stem anatomy Stele of circulartype, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundlespresent, pseudohypodermis absent. Distribution E NorthAmerica. Hybrids 53 x 43. P. xogdenii HELLQ.et R. L. HILTON, Syst. Bot. 8(1): 88. 1983, pro sp. [= P. hillii x P zosteriformis] Note (1) P hillii is closely relatedto P pusillus.Similarto P foliosus, it is recognizableby some constantcharacters in a restrictedarea. 54. Potamogeton obtusifolius MERTENS et W.D.J. KoCH,Rohlings Deutschl. Fl. ed. 3. 1: 855. 1823. = Spirillusobtusifolius(MERT.et W.D.J. KOCH)NIEUWL.,Amer.Midl. Naturalist3: 19. 1913. = P compressusvar.,B.tenuis WAHLENB.,Fl. Upsal.60. 1820. = P compressusvar.et. obtususSCHLTDL., Fl. Berol. 1:117. 1823. = P tataricus LESSING,Linnaea 9: 206. 1834. Taxonomy of Potamogeton 297 = P obtusifolius[var.]a. angustifoliusFIEBER in BERCHT. Fl. Bohm.2(1): 275. 1838; et OPIZ,Oekon.-Techn. FIEBER in BERCHT. et FIEBER,Potam.Bohmens38. 1838. = P. obtusifolius[var.]P. latifoliusFIEBER in BERCHT. et OPIZ,Oekon.-Techn.Fl. Bohm. 2(1): 275. 1838; FIEBER in BERCHT. et FIEBER,Potam. Bohmens 38. 1838. = P foliosus var.diffususA. BENN.,Bot. Soc. Exch. ClubBrit.Isles 6: 860. 1923. Description Rhizomeabsentor present,filiform,slightlycompressed,annual,oftenshortandnot muchdifferentiated from the stem. Stem richly branched,filiform, slightly compressed,annual;apical or axillarydormantturions developing.Submergedleavessessile,linear,(30-)48-85(-100) mmlong,(1.8-)2.5-3.5 mmwide, 15-30(-38) times as long as wide, brightgreento darkgreen,often with a reddishtinge,3(-5)-veined,withoutadditional sclerenchymatous strands,not borderedby a marginalvein, with narrowto broadrows of lacunaebordering the midrib,entireat margins,narrowlycuneateat base,obtuseto roundedat apex,oftenveryshortlyandrather obscurely mucronate.Floating leaves always absent. Stipules axillary,convolute, (6-)10-30 mm long, translucentto opaque,persistent.Peduncles(5-)8-20(-42) mm long, 1-4 times as long as the fruitingspike, as thickas thestem.Spikesshortlycylindrical,7-13 mmlongin fruit,contiguous.Flowers6-8, with(3-)4(-5) carpels.Fruits2.6-3.6 mm long, dorsalkeel indistinctto distinct. Stem anatomy Steleof oblongtype,endodermisof 0-type, interlacunar bundlesabsentora few present,subepidermal bundles present,pseudohypodermis present,1-layered. Distribution Circumpolar, Europe,W andN Asia, N NorthAmerica. Note (1) P obtusifoliusis the most distinctspecies of the P pusillus-group,being easy to identifyin most of its phenotypes. 55. Potamogeton trichoides CHAMISSO et SCHLECHTENDAL, Linnaea 2(2): 175, t. 4, fig. 6. 1827. -P pusillus var. 6. trichoides (CHAM.et SCHLTDL.) KUNTH,Enum.P1.3: 137. 1841. = P pusillusvar.,B.capillarisGAUDIN, FH.Helv. 1: 479. 1828. = P condylocarpus TAUSCH,Flora19(2): 423. 1836. = P trichoidesvar.condylocarpus(TAUSCH) ASCH.et GRAEBN., Synops.Mitteleur.Fl. 1: 347. 1897. = P monogynusJ. GAYin Coss. et GERM.,Suppl.Cat.P1.Env.Paris89. 1843. = P trichoides var.y. monogynus (J. GAY)MAGNIN,Bull. Soc. Bot. France43: 447. 1896. = P tuberculatus TEN. et Guss., Syll. P1.Fl. Neapol.,Append.5: 4. 1842. P trichoidesvar.tuberculatus(TEN. et Guss.) ASCH.,Fl. Brandenb.1: 665. 1864,nom. illeg., non RCHB. 1845. = P trichoides var. P. tuberculosus RCHB.,Icon. Fl. Germ. Helv. 7: 13, t. 22, fig. 35. 1845. = P trichoides var.liocarpus ASCH.,Fl. Brandenb.1: 665. 1864. = P trichoidesvar.trimmeriCASP.,J. Linn.Soc., Bot. 8: 273. 1865. ("Trimmeri") = P baenitziiGAND.,Oesterr.Bot. Z. 31: 19. 1881. ("Baenitzii") = P danicus GAND.,Oesterr.Bot. Z. 31: 18. 1881. = P orthorrhynchus GAND.,Oesterr.Bot. Z. 31: 18. 1881. = P perneglectus GAND.,Oesterr.Bot. Z. 31: 18. 1881. = P phialaePOST,Bull. Herb.Boissier 1(8):409. 1893.("Phialae") = P trichoidesvar.y. phialae (POST)GRAEBN. in ENGL.,Pflanzenr.31 (IV.11): 120. 1907. ("Phialae") Description Rhizomeabsentor presentat the end of the growingseason,filiform,terete.Stemsparinglyto richlybranched, filiform,terete to slightly compressed,annualto perennial;apical or axillarydormantturionsdeveloping. Submergedleaves sessile, linear,14-80(-130) mm long, 0.3-1.0(-1.8) mm wide, (30-)40-80(-l 10) timesas long as wide, brightgreento darkgreen,often with a brownishtinge, 3-veined,lateralveins inconspicuous, withoutadditionalsclerenchymatous strands,notborderedby a marginalvein,withoutrowsof lacunaebordering the midrib,entireat margins,narrowlycuneateat base, acuminateat apex. Floatingleaves always absent. Stipulesaxillary,convolute,5-27 mm long, translucent,often with a greenishtinge, persistent.Peduncles 10-75 mm long, (2-)3-9 times as long as the fruitingspike,as thickas the stem. Spikes shortlycylindrical, 298 G. Wiegleb & Z. Kaplan 3-9 mm long in fruit,contiguousto shortlydistant.Flowers3-5, with 1(-2) carpels.Fruits2.5-3.2 mmlong, dorsalkeel distinct. Stem anatomy Stele of circulartype, endodermisof 0-type, interlacunarbundlesabsent, subepidermalbundlespresent, pseudohypodermis absent. Distribution W, C, S andE Europe,N, E andS Africa,W, SW,N andC Asia. Hybrids 35 x 55. P. xbennetti FRYER,J. Bot. 33: 1, t. 348. 1895. ("Bennettii") [= P. crispusx P trichoides] 48 x 55. P. xgrovesii DANDYet G. TAYLOR, Watsonia 6: 316. 1967. [= P pusillusx P. trichoides] Note (1) P trichoidesis closely relatedto P pusillus.It is sometimesdifficultto distinguishfrommorphotypesof P pusilluswithextremelynarrowleavesin thevegetativestate.Thespeciespossessesa set of uniquecharacters in flowersandfruit,which alwaysmakeidentificationpossible. 56. Potamogeton octandrus POIRETin LAMARCK, Encycl. Meth. Bot., Suppl. 4: 534. 1816. ("octandrum") HydrogetonheterophyllusLOUR., Fl. Cochinch. 1: 244. 1790. ("heterophyllum") [non Potamogeton heterophyllus SCHREB.1771] = P javanicusHASSKARL,Acta Soc. RegiaeSci. Indo-Neerl.1(8):26. 1856. = P tenuicaulisF. MUELL., Fragm.Phyt.Austral.1: 90 et 244. 1858. = P parvifoliusBUCHENAU,Abh. Naturwiss.VereineBremen7: 32. 1882. ("parvifolia") = P miduhikimo MAKINO, Illustr.Fl. Japan1(9):2, tab. 54. 1891. = P octandrusvar.miduhikimo(MAKINO) HARA,J. Jap.Bot. 20: 331. 1944. - P huillensisWELW.ex SCHINZ, Ber.Schweiz.Bot. Ges. 1: 61. 1891,pro syn. ("Huillensis") P limosellifoliusMAXIM.ex KORSH.,TrudyImp. S.-Peterburgsk. Bot. Sada [= Acta HortiPetrop.]12(2): 393. 1893. P. octandrus var.limosellifolius (MAXIM.et KORSH.)TZVELEV in KHARKEV., Sosud.Rast.Sovet.Dal'nego Vostoka2: 323. 1987. = P asiaticusA. BENN., AnnuaireConserv.Jard.Bot. Geneve9: 103. 1905. P. octandrusvar.asiaticus(A. BENN.)TZVELEVin KHARKEV.,Sosud.Rast.Sovet. Dal'negoVostoka2: 323. 1987. = P numasakianus A. BENN.,AnnuaireConserv.Jard.Bot. Gen&ve9: 104. 1905. = P javanicus var. b. major A. BENN.ex GRAEBN. in ENGL.,Pflanzenr. 31 (IV. 1): 161. 1907. - P quinquenervius HAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 130. 1916. - P ligulatusHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 131. 1916. P subfuscusA. BENN.,J. Bot. 65: 114. 1927. - P hubeiensisW.X.WANG, X.Z. SUNet H.Q.WANG,Acta Phytotax.Sin. 26(2): 160. 1988. = P octandrussubsp.ethiopicusLYE,Lidia3(3): 79. 1993. Description Rhizomeabsentor present,filiform,terete,annualor perennial.Stem sparinglyto richlybranched,filiform, terete,annual;axillarydormantturionsdeveloping.Submergedleaves sessile, linear,25-55(-79) mm long, 0.5-1.2(-1.9) mm wide, 30-75 times as long as wide, brightgreento brown-green,3-veined,lateralveins inconspicuous,with very broadrowsof lacunaeborderingthe midrib,entireat margins,straightat base,acute to acuminateat apex.Intermediate leavesoftenpresent,petiolate,oblongto lanceolate.Floatingleavespresent or absent,petiolate;laminalinear-oblongto elliptical,sometimeswith parallelmargins,(5-)9-29(-38) mm long, 3-11 mm wide, 1.3-5.8(-8.5) times as long as wide, opaque,coriaceousto subcoriaceous,brightgreen to darkgreen,sometimeswitha brownishtinge,5-7-veined,cuneateat base,acuteat apex;petiole3-25(-34) mmlong,0.2-1.1 timesas longas the lamina.Stipulesaxillary,convolute,4-13 mmlong,translucent, decaying early.Inflorescenceterminalor lateral,in theaxilsof floatingandsubmergedleaves.Peduncles9-21 mmlong, Taxonomy of Potamogeton 299 0.7-2.4 times as long as the fruiting spike, as thick as or slightly thicker than the stem. Spikes cylindrical, 5-16 mm long in fruit, contiguous to shortly distant. Flowers 7-9, with 4(-5) carpels. Fruits 1.5-2.4 mm long, dorsal keel indistinct to distinct, beak short. Stem anatomy Stele of oblong or circular type, endodermis of 0-type, interlacunar bundles absent, rarely a few present, subepidermal bundles present, pseudohypodermis absent or present, 1-layered. Distribution C and S Africa, S and E Asia, Australia. Hybrids 25 x 56. P. xyamagataensis KADONOet WIEGLEB,J. Jap. Bot. 62(3): 73. 1987. [= P. natans x P octandrus] 56 x 46. P. xkamogawaensis MIKI,Bot. Mag. (Tokyo) 48: 328. 1934. [= P octandrus x P. oxyphyllus] 56 x 48. P. xapertus MIKI,Bot. Mag. (Tokyo) 49: 690.1935. [= P octandrus x P pusillus] Note (1) P. octandrus is a highly polymorphic species with reticulate variation. 57. Potamogeton cristatus REGEL et MAACK in REGEL,Mem. Acad. Imp. Sci. Saint Petersbourg, ser. 7, Sci. Phys.-Math., 4(4): 139, tab. 10, fig. 3-6. 1861. = P iriomotensis MASAMUNE, Trans. Nat. Hist. Soc. Taiwan 24: 281. 1934. Description Rhizome absent or filiform, filiform, terete, annual or perennial, short, with vegetative and generative stems. Stem unbranched or sparingly branched, filiform, terete, annual; axillary dormant turions developing. Submerged leaves sessile, linear, 30-60 mm long, 0.5-1.0 mm wide, 40-80 times as long as wide, bright green to dark green, 3-veined, lateral veins inconspicuous, with broad rows of lacunae along the midrib, entire at margins, straight at base, acute to acuminate at apex. Intermediate leaves often present, petiolate, lanceolate. Floating leaves present or absent, petiolate; lamina broadly lanceolate to oblong or elliptical, 15-27 mm long, 3-11 mm wide, 2.1-5.0 times as long as wide, opaque, subcoriaceous, bright green to dark green, 7-veined, cuneate at base, acute to obtuse at apex; petiole 6-14 mm, 0.2-0.7 times as long as the lamina. Stipules axillary, convolute, 6-10 mm long, translucent, decaying early. Inflorescences mostly lateral, some sometimes terminal, in the axils of floating leaves. Peduncles 10-20 mm long, 0.8-2.0 times as long as the fruiting spike, as thick as the stem, slightly thickened upwards. Spikes 10-15 mm long in fruit, contiguous. Flowers 9-11, with (3-)4 carpels. Fruits 1.5-2.5 mm long, dorsal keel distinct, strongly crested with hooked appendages, beak long and slender. Stem anatomy Stele of circular type, endodermis absent. of 0-type, interlacunar bundles absent, subepidermal bundles absent, pseudohypodermis Distribution East Asia (Japan, Korea, China?, Taiwan). Note (1) P. cristatus is closely related to P octandrus. It is regarded as a distinct species because it shows a number of distinct features in a well defined area. 58. Potamogeton vaseyi J.W. ROBBINSin A. GRAY,Manual Bot. North. U. S. ed. 5. 485. 1867. ("Vaseyi") = P. lateralis MORONG, Bot. Gaz. (Crawfordsville) 5: 51. 1880, p. p. = P vaseyi var. latifolius MORONG, Mem. Torrey Bot. Club 3(2): 44. 1893. Description Rhizome absent or present, filiform, terete, annual or perennial. Stem sparingly to richly branched, filiform, terete, annual; apical or axillary dormant turions developing, in particular on non-flowering shoots. Submerged 300 G. Wiegleb & Z. Kaplan leaves sessile, linear,25-80 mm long, 0.1-0.5 mnmwide, 150-250 times as long as wide, brightgreen to brown-green,3-veined,lateralveins inconspicuous,with narrowrows of lacunaeborderingthe midrib,entire at margins,straightat base, acuminateat apex. Intermediate leaves often present.Floatingleaves presentor absent,petiolate;laminalinear-oblongto ellipticalor obovate,6-15 mm long, 3-8 mm wide, 1.6-2.3 times as long as wide, opaque,coriaceousto subcoriaceous,brightgreento darkgreen,sometimeswith a brownish tinge,5-9-veined, cuneateat base, obtuseat apex;petiole3-25 mm long,0.7-2.0 timesas long as the lamina. Inflorescenceterminalor lateral,in the axils of floatingleaves. Stipulesaxillary,convolute,4-12 mm long, translucent,decayingearly.Peduncles8-16 mm long, 1.0-2.3 times as long as the fruitingspike,as thickas or thickerthanthe stem. Spikes cylindrical,6-8 mm long in fruit,contiguousto shortlydistant.Flowers6, with 4 carpels.Fruits1.6-2.2 mm long, dorsalkeel distinct,beak short. Stem anatomy Stele of one bundletype, endodermisof 0-type, interlacunar bundlesabsent,subepidermalbundlespresent, pseudohypodermis absent. Distribution E NorthAmerica. Note (1) P vaseyiis very similarto P. octandrus.Thereis, however,a largedistributional gap betweenthe two taxa. 59. Potamogeton confervoides REICHENBACH, Icon. Fl. Germ. HeIv. 7: 13. 1845. - P tuckermanii J.W.ROBBINSin A. GRAY,ManualBot. North.U. S. ed. 2. 434. 1856. ("Tuckermani") - P monticolusSCHWEIN. ex A. BENN.,Ann.K. K.Naturhist.Hofmus.Wien7: 292. 1892,prosyn.("monticola") Description Rhizomefiliformto slender,terete,perennial,long creeping,with apicalfusiformturions.Stem sparinglyto richly branched,filiform, terete, annual;apical or axillarydormantturionsdeveloping.Submergedleaves sessile, filiform,(12-)18-65 mm long, 0.1-0.5 mm wide, 50-150 timesas long as wide, brightgreento dark green,sometimeswith a reddishtinge, 1-veined,withoutadditionalsclerenchymatous strands,borderedby a faintmarginalvein, with narrowrows of lacunaeborderingthe midrib,entireat margins,narrowlycuneateat base, long acuminateat apex. Floatingleaves always absent.Stipulesaxillary,convolute,5-12 mm long, translucent,decayingearly.Inflorescence1, rarely2, terminalon primarystem, or rarelyon lower renewal shoots. Peduncles15-240 mm long, 3-25 times as long as the fruitingspike, as thick as the stem. Spikes subgloboseto cylindrical,3-12 mm long in fruit,contiguous.Flowers3-5, with4 carpels.Fruits2.2-3.0 mm long, dorsalkeel distinct. Stem anatomy Stele of oblongtype, endodermisof 0-type with strongcell walls, interlacunar bundlesabsent,subepidermal bundlesrarelya few present,pseudohypodermis present,1-2-layered. Distribution E NorthAmerica. Note (1) P confervoidesis an isolatedspecies withinthe subgenusPotamogeton. 60. Potamogeton spirillus TUCKERMAN, Amer. J. Sci. Arts, Ser. 2, 6: 228. 1848. Zannichelliapalustrisvar.gyrocarpaTRIMEN,J. Bot. 12: 370. 1874. - Spirillustuckermannii J. GAYex A. BENN.,J. Bot. 28: 298. 1890,pro syn. ("Tuckermanni") - ZannichelliacochlospermaA. BRAUNex A. BENN.,J. Bot. 28: 298. 1890, pro syn. ("Cochlospermum") Description Rhizome slender,compressed,perennial,with overwinteringleafy short shoots. Stem sparinglyto richly branched,filiformto slender,compressed,annual;specializeddormantturionsnot developing.Submerged leavessessile, linear,8-80 mmlong,0.5-2.0 mmwide, 15-80 timesas long as wide,brightgreen,1-3-veined, withoutadditionalsclerenchymatous strands,not borderedby a marginalvein, usuallywith narrowrows of lacunaeborderingthe midrib,entire at margins,straightat base, obtuse to acute at apex. Stipulesof the submergedleaves adnate,convolute, 2-12 mm long, fused with the leaves for 1.5-6.0 mm, translucent, persistent.Intermediateleaves often present.Floatingleaves shortlypetiolate;laminaoblong to elliptic or - Taxonomy of Potamogeton 301 ovate-elliptic,7-35 mm long, 2-13 mm wide, 2-4 timesas long as wide, opaque,subcoriaceous,brightgreen to darkgreen,5-13-veined, cuneateto roundedat base, obtuseat apex;petiole5-25 mm long, 0.7-1.1 times as long as the lamina.Stipulesof thefloatingleavesaxillary,convolute,3-15 mm long,translucent, persistent. Inflorescencesdimorphicto trimorphic.Peduncleof inflorescencesin the axils of the submergedleaves 1-3 mm long, 0.5-1.0 times as long as the fruitingspike,as thickas the stem;spikeglobose to subglobose,2-5 mm long in fruit,contiguous.Spikeof inflorescencesin the axils of the intermediate leaves andlowerfloating leaves subglobose,4-7 mmlong in fruit,contiguous.Peduncleof inflorescencesin the axils of floatingleaves 4-27 mmlong,0.8-2.3 timesas long as the fruitingspike,as thickas the stem;spikesubgloboseto cylindrical, 5-14 mm long in fruit,contiguous.Flowers1-6 in submergedspikes,2-8 in emersedspikes,with4 carpels. Fruits1.3-2.4 mm long, dorsalkeel distinct,sharp,entire,lateralkeels absent,embryocoiledmorethan1 turn. Stem anatomy Stele of trio type, endodermisof 0-type, interlacunar bundlesabsent,subepidermalbundlespresent,faint, pseudohypodermis absent. Distribution C andE NorthAmerica. Note (1) P. spirillusis closely relatedto P diversifolius. 61. Potamogeton diversifolius Rafinesque, Med. Repos., Hexade 3, 2: 409. 1811. ("diversifolium") - P diversifoliusRAF.,Med. Repos.,Hexade2, 5: 354. 1808,nom. prov.("diversifolium") - P. diversifoliusvar.capitatusENGELM., Amer.J. Sci. Arts46: 102. 1844, nom. inval. _ Spirillusdiversifolius(RAF.)NIEUWL.,Amer.Midl.Naturalist3: 18. 1913. = P capillaceusPOIR.in LAM.,Encycl.Meth.Bot., Suppl.4: 535. 1816. ("capillaceum") = P dimorphusRAF., Amer.Month.Mag. Crit.Rev. 1: 358. 1817. ("dimorphum") = P diversifoliusvar.spicatusENGELM., Amer.J. Sci. Arts,46: 102. 1844. = P diversifoliusvar.multidenticulatus MORONG, Mem.TorreyBot.Club3(2):48. 1893.("multidenticulatus") P hybridusvar. [. multidenticulatus (MORONG) GRAEBN. in ENGL.,Pflanzenr.31 (IV.11): 51. 1907. ("multidenticulatus") -P tricostatusWALLR.ex GRAEBN.in ENGL., Pflanzenr.31 (IV.11): 51. 1907, pro syn. ? P spirilliformisHAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 137. 1916. - P conjungens HAGSTR., Kungl.SvenskaVetenskapsakad. Handl.55(5): 138. 1916. - P dimorphoides HAGSTR.,Kungl.SvenskaVetenskapsakad. Handl.55(5):263. 1916,prohybr.P diversifolius (sub P dimorphus)x P pusillus. - P capillaceusvar.atripesFERNALD, Rhodora39: 380. 1937. ? P reniacoensisSPARRE, Bol. Soc. Argent.Bot. 6(2): 107. 1956. Description Rhizomefiliformto slender,compressed,perennial.Stem richlybranched,filiformto slender,compressedto subterete,annual;axillarydormantturionsdeveloping.Submergedleaves sessile, linear,(10-)20-65(-l 10) mm long, (0.2-)0.4-1.0(-l.5) mm wide, 20-180(-280) times as long as wide, brightgreen to darkgreen, 1(-3)-veined,withoutadditionalsclerenchymatous strands,not borderedby a marginalvein, with or without narrowrowsof lacunaeborderingthe midrib,entireat margins,straightat base,narrowlyobtuseto acuminate at apex. Stipulesof the submergedleaves adnate,convolute,2-6(-18) mm long, fused with the leaves for 0.3-4.0(-7.0) mm, translucent,persistent.Intermediate leavesoftenpresent.Floatingleaves shortlypetiolate; laminaoblongto ellipticor orbicular-elliptic, (7-)13-40 mmlong,(2-)4-17(-20) mm wide,2-4 timesas long as wide, opaque,subcoriaceous,brightgreento darkgreen,(3-)5-l5(-17)-veined, cuneateto roundedat base, acuteto roundedat apex;petiole2-40 mm long, 0.6-1.2 times as long as the lamina.Stipulesof the floating leaves axillary to slightly adnate, convolute, (2-)7-25 mm long, translucent,persistent.Inflorescences dimorphic.Peduncleof inflorescencesin the axils of the submergedleaves 1-8 mm long, 0.5-1.5 times as long as the fruitingspike,as thickas the stem;spikegloboseto subglobose,2-6 mm long in fruit,contiguous. Peduncleof inflorescencesin the axils of floatingleaves3-32 mm long, 0.8-1.4 times as long as the fruiting spike,as thickas the stem;spike subgloboseto cylindrical,3-28 mm long in fruit,contiguous.Flowers1-8 302 G. Wiegleb & Z. Kaplan in submergedspikes,4-30 in emersedspikes,with4 carpels.Fruits0.9-2.0(-2.2) mmlong,dorsalkeel distinct, sharp,dentate,lateralkeels usuallypresent,entireto dentate,embryocoiled morethan 1 turn. Stem anatomy Stele of triotype, endodermisof 0-type, interlacunar bundlesabsentor rarelypresent,subepidermal bundles absentor a few present,pseudohypodermis absentor partlypresent,1-layered. Distribution NorthAmerica,SE SouthAmerica. Note (1) DespitetheirremoteoccurrenceSouthAmericanplants(likee.g. P.spirilliformis) areregardedas conspecific with NorthAmericanones. However,theirvariationis insufficientlyknown. 62. Potamogeton bicupulatus FERNALD, Mem. Amer. Acad. Arts Sci. 17: 112. 1932. P diversifolius var. trichophyllus MORONG, Mem.Torrey Bot. Club 3(2): 49. 1893. _ P hybridusvar.y. trichophyllus(MORONG) GRAEBN. in ENGL.,Pflanzenr.31 (IV.11): 51. 1907. Description Rhizomefiliform,compressed,perennial.Stemsparinglyto richlybranched,filiform,terete,annual;specialized dormantturionsnot developing.Submergedleavessessile, setaceous,30-1 10 mmlong,0.08-0.40(-0.50) mm wide, (140-)190-500(-600) times as long as wide, brightgreento darkgreen, 1-veined,withoutadditional sclerenchymatous strands,not borderedby a marginalvein, withoutrows of lacunaeborderingthe midrib, entireat margins,straightat base,acuminateat apex.Stipulesof the submergedleavesadnate,convolute,2-12 mm long, fused with the leaves for 0.3-3.5 mm, translucent,persistent.Intermediateleaves often present. Floatingleaves shortlypetiolate;laminaoblongto broadlyelliptic,6-23(-28) mm long, 2-11 mm wide, 2-5 times as long as wide, opaque,subcoriaceous,brightgreento darkgreen,5-15-veined,cuneateto roundedat base,acuteat apex;petiole5-35 mm long, 0.8-1.4 timesas long as the lamina.Stipulesof the floatingleaves axillary,convolute,3-1 1 mmlong,translucent, persistent.Inflorescences dimorphic.Peduncleof inflorescences in the axils of the submergedleaves 1-10 mm long, 0.5-1.5 timesas long as the fruitingspike,as thickas the stem;spikeglobose to subglobose,2-7 mm long in fruit,contiguous.Peduncleof inflorescencesin the axils of floating leaves 3-22 mm long, 1.0-1.9 times as long as the fruitingspike, as thick as the stem; spike subgloboseto cylindrical,3-14 mm long in fruit,contiguous.Flowers 1-8 in submergedspikes, 2-10 in emersedspikes, with 4 carpels.Fruits(l.l-)1.6-2.0 mm long, dorsalkeel distinct,sharp,entireto dentate, lateralkeels usuallypresent,entireto dentate,embryocoiled morethan1 turn. Stem anatomy Not seen. Distribution C andE NorthAmerica. Note (1) P bicupulatusis closely relatedto P diversifolius andmay be regardedas an extrememorphotypeof that speciesundera widerspecies concept. 63. Potamogeton vaginatus TURCZANINOW, Bull. Soc. Imp. Naturalistes Moscou 27(3): 66. 1854. -P. vaginatusTURCZ., Bull. Soc. Imp.NaturalistesMoscou 11(1): 102. 1838, nom. nud. P pectinatus subsp. vaginatus (TURCZ.)MAGNIN,Bull. Soc. Bot. France 43: 447. 1896. _ P.pectinatus var. vaginatus (TURCZ.)ASCH.et GRAEBN.,Synops. Mitteleur. Fl. 1: 351. 1897. Stuckeniavaginata(TURCZ.) HOLUB, Folia Geobot.Phytotax.19(2):215. 1984. Coleogetonvaginatus(TURCZ.) LESet R.R. HAYNES, Novon 6(4): 390. 1996. = P moniliformis H. ST. JOHN,Rhodora 18: 130. 1916. = P vaginatus var. canadensis HAGSTR., Kungl. Svenska Vetenskapsakad. Handl. 55(5): 36. 1916. - P. canadensis HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 36. 1916, nom. prov. Description Rhizomeslenderto robust,terete,perennial,with apicaltubers.Stem richly branched,with severalrenewal shootsspringingfromone node, slender,terete,annualto perennial,wintergreen;specializeddormantturions not developing.Submergedleaves sessile, filiformto linear,20-120(-150) mm long, 1-2 mm wide, 20-130 Taxonomy of Potamogeton 303 times as long as wide, olive green to dark green, often with a greyish tinge, 1-3-veined, lateralveins inconspicuous,withair channelsborderingthe midrib,entireat margins,straightat base,obtuseto sometimes slightlysubretuseat apex.Floatingleavesalwaysabsent.Stipulesadnate,connate,20-50(-70) mmlong, 2-10 mm wide, fused with the leaves for 17-45(-65) mm, persistent.Peduncles30-150(-200) mm long, 1.5-4.5 timesas long as the fruitingspike,as thickas the stem.Spikescylindrical,25-70 mm long in fruit,contiguous to distant.Flowers14-16(-20), with4 carpels.Fruits3.0-3.8 mm long, dorsalkeel indistinct. Stem anatomy Stele of trio or four bundles type, endodermisof U-type, interlacunarbundlespresent in (3-)4 circles, subepidermal bundlesabsent,rarelya few present,pseudohypodermis present,1-2-layered. Distribution Circumboreal; N Europe,N Asia, N NorthAmerica. Hybrids 66 x 63. P. xfennicus HAGSTR., Kungi.Svenska Vetenskapsakad.Handl.55(5): 24. 1916. [= P.filiformisx P. vaginatus] -Stuckenia xfennica (HAGSTR.)HOLUB,Preslia 69: 364. 1997. 68 x 63. P. xbottnicus HAGSTR., Kungi.Svenska Vetenskapsakad.Handl.55(5): 52. 1916. [= P pectinatusx P vaginatus] Stuckenia xbottnica (HAGSTR.)HOLUB,Preslia 69: 364. 1997. Note (1) P. vaginatusis a well defined species which, until recently,has been sometimesconfusedwith its own hybridsand wintergreenformsof P. pectinatus. 64. Potamogeton subretusus HAGSTROM, Kungl. Svenska Vetenskapsakad. Handl. 55(5): 30. 1916. = Stuckenia subretusa (HAGSTR.)HOLUB,Preslia 69: 364. 1997. Description Rhizomeslender,terete,perennial,withapicaltubers.Stemsparinglyto richlybranched,slender,terete,annual to perennial;specializeddormantturionsnot developing.Submergedleaves sessile, filiformto linear,20-100 mmlong,0.6-1.3(-1.5) mm wide, 25-90 timesas long as wide,olive greento darkgreen,oftenwitha greyish tinge,3-5-veined,lateralveins inconspicuous,withairchannelsborderingthemidrib,entireat margins,straight at base, obtuse to distinctly subretuseat apex. Floating leaves always absent. Stipules adnate,connate, 20-30(-40) mm long, 1.5-4.0 mm wide, fused with the leaves for 18-26(-35) mm, persistent.Peduncles 100-170(-200) mm long, 2-5 times as long as the fruitingspike, as thick as the stem. Spikes cylindrical, 20-50 mm long in fruit,contiguousto distant.Flowers6-16, with 4 carpels.Fruits2.2-3.0 mm long, dorsal keel indistinct. Stem anatomy Steleof 4 bundlestype,endodermisof U-type,interlacunar bundlespresentin 1 incompletecircle,subepidermal bundlesabsent,pseudohypodermis absent. Distribution NE Europe,N Asia, NW NorthAmerica. Note (1) P. subretususis closely relatedto P vaginatusandin the futuremaybe regardedas an extrememorphotype of thatspecies. 65. Potamogeton recurvatus HAGSTROM, Kungi. Svenska Vetenskapsakad. Handl. 55(5): 37. 1916. Description Rhizomeslenderto robust,terete,perennial,with apical tubers.Stem branched,slender,terete,annualto perennial;specializeddormantturionsnot developing.Submergedleaves sessile, linear,stronglyrecurvedat the top, (40-)50-120(-500) mm long, 1.0-1.6 mm wide, 30-100 timesas long as wide, brightgreento olive green,3-veined,lateralveins inconspicuous,withairchannelsborderingthe midrib,entireat margins,straight 304 G. Wiegleb & Z. Kaplan at base, obtuseat apex. Floatingleaves alwaysabsent.Stipulesadnate,connate,7-140 mm long, fused with the leaves for 5-120 mm, persistent.Peduncles20-50 mm long, 1-2 times as long as the fruitingspike,as thickas thestem.Spikescylindrical,contiguousto distant.Flowerandcarpelnumbersunknown.Fruits3.0-3.5 mm long, dorsalkeel indistinct. Stem anatomy Stele of four bundlestype, endodermisof U-type,interlacunar bundlespresentin 1-2 circles, subepidermal bundlespresent,pseudohypodermis present,1-layered. Distribution C Asia. Note (1) P recurvatushas been describedon the basis of a few specimensonly. It is insufficientlyknown,but perhaps related to P vaginatus. 66. Potamogeton filiformis PERSOON,Syn. Pi. 1: 152. 1805. ("filiforme") P setaceus SCHUMACH., Enum. P1. 1: 51. 1801, nom. illeg. ("setaceum"), non L. 1753. P pectinatus var. P. setaceus [SCHUMACH.] C. HARTM,Handb. Skand. Fl. ed. 11. 437. 1879. P pectinatus subsp. filiformis (PERS.)HOOK.f., Stud. FH.Brit. Isl. 374. 1870. Stuckenia filiformis (PERs.) BORNER,Fl. Deutsche Volk 713. 1912. Spirillusfilifonnis (PERS.)NIEUWL.,Amer. Midi. Naturalist 3: 18. 1913. Coleogetonfiliformis (PERS.)LES et R.R. HAYNES,Novon 6(4): 390. 1996. = P borealis RAF., Med. Repos., Hexade 3, 2: 409. 1811. - P borealis RAF., Med. Repos., Hexade 2, 5: 354. 1808, nom. prov. P filiformis var. borealis (RAF.)H. ST. JOHN,Rhodora 18: 134. 1916. Stuckenia borealis (RAF.)HOLUB,Preslia 69: 364. 1997. = P fasciculatus WOLFG.in SCHULT.et SCHULT. f., Mant. 3: 364. 1827. - P filiformis var.fasciculatus (WOLFG.)G. FISCH.,Ber. Bayer. Bot. Ges. 11: 132. 1907. = P strictus PHIL.,Fl. Atacam. 50. 1860. [non vidimus] = P marinusvar.alpinusBLYTr,Norges Fl. 1: 370. 1861. P filiformis var. P. alpinus (BLYrF) ASCH.et GRAEBN.,Synops. Mitteleur. Fl. 1: 353. 1897. Coleogetonfiliformis subsp. alpinus (BLYTr)LES et R.R. HAYNES,Novon 6(4): 390. 1996. = P marinus var. occidentalis J.W. ROBBINSin S. WATSON,U.S. Geol. Explor. Fortieth Parallel 5(Botany): 338. 1871. P filiformis var. occidentalis (J.W. ROBBINS)MORONG,Mem. Torrey Bot. Club 3(2): 51. 1893. P interior RYDB., Agric. Exp. Stat. Agric. Coll. Colorado Bull. [Fl. Colorado] 13. 1906. ("1905") Coleogetonfiliformis subsp. occidentalis (J.W. ROBBINS)LES et R R. HAYNES,Novon 6(4): 390. 1996. Stuckenia interior (RYDB.) HOLun, Preslia 69: 364. 1997. = P marinus var. macounii MORONGex MACOUN,Catal. Canad. P1. 4: 88. 1888. ("Macounii") P filiformis var macounii (MORONGex MACOUN)MORONG,Mem. Torrey Bot. Club 3(2): 50. 1893. = P aulacophyllus K. SCHUM.in MART.,Fl. Bras. 3, 3: 696. 1894. ("aulacophyllum") = P juncifolius A. KERN.ex C. FRITSCH,Verh. K. K. Zool.-Bot. Ges. Wien, 45(1895): 366. 1896. _ P filiformis subsp. juncifolius (A. KERN.ex C. FRITSCH)ASCHERS.et GRAEBN.,Synops. Mitteleur. Fl. ed. 2. 1: 544. 1913. P.filiformis var.juncifolius (A. KERN.ex C. FRITSCH)SUESS.in HEGI,Ill. Fl. Mitt.Europ. ed. 2. 1: 202. 1936. = P strictus var. magellanicus HAGSTR.,Kungl. Svenska Vetenskapsakad.Handl. 55(5): 27. 1916. = ? P. rostratus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 27. 1916. = P austrosibiricus KASCHINAin KRASNOB.et SAFONOVA, Novoe Fl. Sibiri 243. 1986. ("austrosibiricus") = P applanatusY.D. CHEN,Acta Hydrobiol. Sin. 11(3): 230. 1987. = P filiformis var. applanatus (Y.D. CHEN)Q.Y. Li, J. Wuhan Bot. Res. 10(1): 13. 1992. = ? P punense GALAN-MERA,Phytologia 64(6): 495. 1988. Description Rhizome slender, terete, perennial, with apical tubers. Stem unbranchedto sparingly branched, slender, terete, annual to perennial; specialized dormant turions not developing. Submerged leaves sessile, filiform, Taxonomy of Potamogeton 305 30-175(-240) mm long, 0.3-1.2(-1.9) mnm wide, (50-)100-300 times as long as wide, olive greento dark green,sometimeswith a greyishtinge, 3-veined,lateralveins inconspicuous,with air channelsborderingthe midrib,entireat margins,straightat base, obtuseto subacuteat apex.Floatingleaves alwaysabsent.Stipules adnate,connate,8-27(-55) mmlong,fusedwiththeleavesfor3-1 9(-50) mm,persistentto decaying.Peduncles (25-)50-190(-220) mm long, 2-5(-6) times as long as the fruitingspike, as thick as the stem, terminalon primarystem or on first orderrenewalshoots.Spikescylindrical,13-75 mm long in fruit,markedlydistant. Flowers4-1 1, with 4(-6) carpels.Fruits(1.9-)2.2-2.8(-3.2) mm long, dorsalkeel indistinct. Stem anatomy Stele of fourbundlesor rarelyoblongtype,endodermisof U-type,rarely0-type, interlacunar bundlespresent in 1(-3) incompletecircles, subepidermal bundlesabsent,pseudohypodermis present,1-2-layered. Distribution Europe,W, C andN Asia, NorthAmericaandSouthAmerica. Hybrids 66 x 63. P. xfennicus HAGSTR.,Kungi.Svenska Vetenskapsakad.Handl.55(5): 24. 1916. [= P filiformisx P vaginatus] 66 x 68. P xsuecicus K. RICHT., Pi. Eur. 1: 15. 1890. [= P.filiformisx P pectinatus] _ Stuckeniaxsuecica(K. RICHT.)HOLUB,Preslia69: 364. 1997. Notes (1) P filiformisis a widespreadpolymorphicspecies.It includesseveralaberrant morphotypeslikeP rostratus. (2) P. strictusdiffers from the type in some anatomicalcharactersof stem structure(e.g. stele regularlyof oblong type). Despite being geographicallyremotefrom the rest of the species, no furtherdistinguishing characterwas found. 67. Potamogeton amblyphyllus C.A. MEYER,Beitr. Pflanzenk. Russ. Reiches 6: 10. 1849. ("amblyophyllus") = P pectinatusprolesamblyphyllus(C.A. MEY.)GRAEBN.in ENGL.,Pflanzenr.31 (IV.11): 125. 1907. = Stuckeniaamblyphylla(C.A. MEY.)HOLUB,Preslia69: 364. 1997. ? P pamiricusBAAGOE,Vidensk.Meddel.DanskNaturhist.Foren.Kjobenhavn1903: 182. 1903. Description Rhizomeslender,terete,perennial,with apicaltubers.Stemunbranched to sparinglybranched,slender,terete, annualto perennial;specializeddormantturionsnot developing.Submergedleaves sessile, filiform,30-120 mm long, 1-3 mm wide, 20-50 times as long as wide, olive green to darkgreen, 3-veined, lateralveins inconspicuous,with air channelsborderingthe midrib,entireat margins,straightat base, obtuse at apex. Floatingleaves alwaysabsent.Stipulesadnate,connate,10-35 mm long, fusedwith the leaves for 5-20 mm, persistent.Peduncles50-80 mm long, 1.5-3.0 timesas long as the fruitingspike,as thickas the stem.Spikes cylindrical,30-35 mmlong in fruit,distant.Flowers9-12, with4 carpels.Fruits(2.8-)3.0-3.5 mmlong,dorsal keel indistinct. Stem anatomy Stele of four bundles type, endodermisof U-type, interlacunarbundles present as 1 incompletecircle, subepidermal bundlesabsent,pseudohypodermis present,1-2-layered. Distribution SW andC Asia. Note (1) P amblyphyllus is closely relatedto P filiformis.It comprisesmorerobustformsof a restrictedgeographical area. P pamiricus is included in this concept of P amblyphyllus. 68. Potamogeton pectinatus LINNAEUS, Sp. Pi. 127. 1753. ("pectinatum") = Stuckenia pectinata (L.) BORNER,Fl. Deutsche Volk 713. 1912. = Spirilluspectiniformis[L.] NIEUWL.,Amer.Midl.Naturalist3: 18. 1913. 306 G. Wiegleb & Z. Kaplan - Coleogeton pectinatus (L.) DOSTAL,Sezn. Cevn. Rostl. Kvet. Ceskosl. 309. 1982, nom. inval.; DOSTAL, Folia Mus. Rer. Natur. Bohem. Occid., Bot., 21: 15. 1984, nom. inval. Coleogeton pectinatus (L.) LES et R.R. HAYNES,Novon 6(4): 390. 1996. = P marinusL., Sp. PI. 127. 1753. ("marinum") = P interruptusKIr.in SCHULT.,Oesterr. Fl. ed. 2. 1: 328. 1814. -P pusillus [var.] P. interruptus (KIT.) J. PRESLet C. PRESL,Fl. (tech. 37. 1819. P. pectinatus var. interruptus (KiT.) ASCH.,Fl. Brandenb. 1: 666. 1864. = P pectinatusproles interruptus(KIr.)GRAEBN.in ENGL.,Pflanzenr. 31 (IV. 11): 124. 1907. Spirillusinterruptus(KIT.)NIEUWL.,Amer. Midl. Naturalist 3: 18. 1913. = P tenuifoliusKUNTH in HUMB.,BONPL.et KuNTH, Nov. Gen. Sp. P1. 1, ed. 40: 370 [et ed. f: 297]. 1815, nom. illeg. ("tenuifolium"), non Raf. 181 1. = P angustissimusKUNTH in HUMB., BONPL.et KUNTH,Nov. Gen. Sp. P1. 1, ed. 4?: 370 [et ed. f?: 297]. 1815. ("angustissimum") = P vaillantii ROEM.et SCHULT.,Syst. Veg. ed. 16. 3: 514. 1818. ("Vaillantii") _ P pectinatus [var.] ("spielart") a. latifolius G. MEY.,Chloris Han. 526. 1836. = P siculus J. PRESLin BERCHT.et J. PRESL,Rostlinar 1,.fasc. Zabnjkowite 21. 1821. ("siculum") = P pectinatusvar. P. dichotomusWALLR.,Sched. Crit. 1: 68. 1822. = P pectinatusvar. a. protensusWALLR.,Sched. Crit. 1: 67. 1822. = P pectinatusvar. Y. scopariusWALLR.,Sched. Crit. 1: 68. 1822. P pectinatus var. diffusus HAGSTR.,Kungl. Svenska Vetenskapsakad. Handl. 55(5): 46. 1916, nom. illeg. P pectinatusproles scoparius(WALLR.)GRAEBN.in ENGL.,Pflanzenr. 31 (IV.11): 125. 1907. P diffusus[HAGSTR.]HERTER,Revista Sudamer. Bot. 6(5-6): 132. 1940. [non vidimus] = P zosteraceus FR.,Novit. Fl. Suec. ed. 2. 51. 1828. = P pectinatus var. zosteraceus (FR.)CASP., Schriften Phys.-Okon. Ges. Konigsberg 29: 89. 1888. = P pectinatusproles zosteraceus(FR.) GRAEBN.in ENGL.,Pflanzenr. 31 (IV.1 1): 126. 1907. = P pectinatus [subsp.] P. fluviatilis SCHUBL.et G. MARTENs,Fl. Wurttemb. 112. 1834. = P drupaceus0. LANG,Flora29(30):472. 1846. = P flabellatusBAB., Man.Brit.Bot. ed. 3. 343. 1851. P pectinatussubsp. flabellatus(BAB.) HOOK.f., Stud. Fl. Brit. Isl. 374. 1870. _ P pusillus subsp. flabellatus (BAB.) HOOK.f., Stud. Fl. Brit. Isl. ed. 3. 436. 1884. ? P pectinatusvar.mongolicusA. BENN.,J. Bot. 32: 203. 1894. ? P pectinatusproles mongolicus(A. BENN.)GRAEBN.in ENGL.,Pflanzenr. 31 (IV.11): 125. 1907. ? P pectinatus subsp. mongolicus (A. BENN.)VOLOB.,Sibir. Biol. Zhurn. 1991(5): 75. 1991. = P columbianus SUKSDORF,Deutsche Bot. Monatsschr. 19: 92. 1901. = P livingstoneiA. BENN.in DYER,Fl. Trop. Afr. 8: 223. 1901. ("Livingstonei") = P vaginatusvar. helveticusG. FISCH.,Ber. Bayer. Bot. Ges. 11: 134. 1907. = P vaginatussubsp. helveticus(G. FISCH.)SCHINZet THELL.,Fl. Schweiz ed. 4. 1: 32. 1923. = P helveticus (G. FIsCH.) W. KOCH in W. KOCHet G. KUMMER,Mitt. Naturf. Ges. Schaffhausen - 1923-1924(3):38. 1924. P helveticus (G. FISCH.)E. BAUMANN,Veroff. Geobot. Inst. ETH Stiftung Rubel Zurich 3(5): 594. 1925. [isonymum] P pectinatus var. helveticus (G. FISCH.)GLUCKin PASCHER,Susswasserflora 15: 62. 1936. Stuckenia helvetica (RAF.)HOLUB,Preslia 69: 364. 1997. - P helveticusvar.balatonicusGAMS,Arch.Balaton.1: 30. 1926. P balatonicus (GAMS)So0, Arch. Balaton. [= Magyar Biol. Kutat6int. Munkai], 2: 136. 1928. P.pectinatus subsp. balatonicus (GAMS)S06, Magyar Biol. Kutat6int. Munkai 8(1935-1936): 235. 1936. - Coleogetonpectinatussubsp. balatonicus(GAMS)DoSTAL,Sezn. Cevn. Rostl. Kvet. C-eskosl. 309. 1982, nom inval.; (GAMS)DoSTAL, Folia Mus. Rer. Natur. Bohem. Occid., Bot., 21: 15. 1984, nom. inval. -? P pectinatusvar.gracilisKUZMINet SKVORTZOV in BARANOVet SKVORTZOV, Diagn. P1.Nov. Min. Cogn. Mandsch. 1. 1943. P macrocarpus DOBROCHOT., Bot. Mat. Gerb. Bot. Inst. Akad. Nauk SSSR [= Not. Syst. Herb. Inst. Bot. Acad. Sci. URSS] 14: 70. 1951. -P intramongolicus Y.C. MA, ActaBot. Bor.-Occid. Sin. 3(1): 8. 1983, nom. inval.; YC. MA, Fl. Intramongolica 7: 12. 1983, nom. inval. Taxonomy of Potamogeton 307 - P acifolius Y.C. MA, Acta Bot. Bor.Occid. Sin. 3(1): 10. 1983, nom. inval. = P pectinatus subsp. chakassiensis KASCHINAin KRASNOB.et SAFONOVA, Novoe o Fl. Sibiri 245. 1986. P. chakassiensis (KASCHINA)VOLOB.,Sibir. Biol. Zhum. 1991(5): 75. 1991. Description Rhizomeslenderto very robust,terete,perennial,with apicaltubersat the end of the growingseason.Stem sparinglyto richly branched,filiform to slender,terete,annualto perennial,summergreenor wintergreen; specializeddormantturionsnot developing,sometimeswith winterbudsas axillaryleafy shoots.Submerged leaves sessile, filiformto linear,22-125(-200) mm long, 0.2-4.0 mm wide, 24-160(-200) times as long as wide, brightgreen to olive green, 3-5-veined, lateralveins inconspicuous,with air channelsborderingthe midrib,entireat margins,straightat base, acuminateto acuteat apex, sometimesthe broadestleaves obtuse. Floatingleaves always absent.Stipulesadnate,convolute,10-70 mm long, fused with the leaves for 8-65 mm,persistent.Peduncles20-130(-450) mmlong, 1.5-5.0(-10.0) timesas long as the fruitingspike,as thick as the stem, flexible. Spikes cylindrical,13-60 mm long in fruit,contiguousat first, laterdistant.Powers (4-)8-14, with4 carpels.Fruits3.3-4.7(-5.1) mm long, dorsalkeel indistinct. Stem anatomy Stele of fourbundles,oblongor rarelyI circulartype, endodermisof U-type,interlacunar bundlespresentin 1 more or less complete circle, subepidermalbundles absent,rarelypresent,pseudohypodermis present, 1-2-layered. Distribution Cosmopolitan;Europe,Africa,Asia, Australia,NorthAmericaand SouthAmerica. Hybrids ? 25 x 68. P. xnomotoensis KADONO et T. Noguchi, Acta Phytotax.Geobot. 42(2): 175. 1991, pro sp. [= ? P natansx P. pectinatus] 68 x 63. P. xbottnicus HAGSTR., Kungi.Svenska Vetenskapsakad.Handl.55(5): 52. 1916. [= P pectinatusx P vaginatus] 66 x 68. P. xsuecicus K. RICHT., PI. Eur.1: 15. 1890. [= P filiformisx P pectinatus] Notes (1) P pectinatusis an extremelypolymorphicspecies with numerouslocal and regionalforms as well as extremeecomorphoses. (2) RobustwintergreenformscalledP helveticusareoccasionallyfoundin riversandlargeclear-waterlakes. Theircharactersare not stablewhen transplantated into cultivationand they are producedrepeatedlyunder specialecologicalcircumstances.The exact relationshipof these similarplantsknownfrom distantareasis unknown. (3) P chakassiensiscomprisesa set of formswith stipulesand leaves considerablylongerthanin the type. However,they do not deservespecificrank(KAPLAN 1995). 69. Potamogeton striatus Ruiz et PAVON,Fl. Peruv. Chil. 1: 70. 1798. ("striatum") P pectinatus var striatus (RUIz et PAV.)HAGSTR.,Kungi. Svenska Vetenskapsakad. Handl. 55(5): 51. 1916. Coleogeton striatus (RuIz et PAV.)LES et R.R. HAYNES,Novon 6(4): 390. 1996. Stuckenia striata (RuIz et PAV.)HOLUB,Preslia 69: 364. 1997. = P pectinatus var. latifolius J.W. ROBBINSin S. WATSON,U. S. Geol. Explor. Fortieth Parallel 5(Bot.): 338. 1871, nom. illeg., non G. MEY1836. P latifolius [J.W. ROBBINS]MORONG,Mem. Torrey Bot. Club 3(2): 52, tab. 59. 1893. nom. illeg., non SLOBODA1852. P filiformis var. latifolius [J.W. ROBBINS]REVEALin CRONQUIST et al., Intermountain Fl., Vasc. P1. Intermountain West,USA 6: 26. 1977. P latiorHOLUB, Folia Geobot.Phytotax.18(2):204. 1983. = P australis F. PHIL.,Anal. Mus. Nac. Chile 2(8): 95. 1891. [non vidimus] = P dissimilis A. BENN., J. Bot. 48: 150. 1910. 308 G. Wiegleb & Z. Kaplan Description Rhizomeslender,terete,perennial,withoutapicaltubers.Stem sparinglyto richlybranched,slender,terete, annualto perennial;specializeddormantturionsnot developing.Submergedleavessessile, linear,50-210 mm long, 0.4-5.1 mm wide, 35-150 times as long as wide, brightgreento darkgreen,3-7-veined, lateralveins inconspicuous,with air channelsborderingthe midrib,entireat margins,straightat base, acute to obtuseat apex,sometimesthe broadestleaves obtuse.Floatingleaves alwaysabsent.Stipulesadnate,convolute,12-34 mm long, fused with the leaves for 9-28 mm,persistent.Peduncles12-54 mm long, 0.8-2.0 timesas long as the fruitingspike, as thick as or slightlythinnerthanthe stem. Spikescylindrical,17-60 mm long in fruit, contiguousat the beginning,distantlater.Flowers7-16, with 4 carpels.Fruits3.0-3.9 mm long, dorsalkeel indistinct. Stem anatomy Stele of complexoblongtypeor rarelycirculartype,endodermisof U-type,rarely0-type, interlacunar bundles presentin 1-2 incompletecircles, subepidermal bundlesabsent,pseudohypodermis 1(-2)-layered. Distribution W andSW NorthAmenrcaandSouthAmerica. Note (1) P striatus has often been treated as a subunit of P. pectinatus. Even though both species are closely related the differentialcharactersseem to be constantthroughoutthe rangeof P. striatus. The separatepositionof the species has been recentlysupportedby an isozymestudy(HOLLINGSWORTH et al. 1996).The relationshipto morphologically similarplantsknownfromEuropeandAsia, hereincludedin P.pectinatus, has to be clarified. CONCLUSIONS In the preceeding paragraphsa large bulk of informationregardingthe description and identification of Potamogeton species has been compiled. The present treatment can be summarizedas follows: (1) A total of 69 species are described. In several cases it was easier to constructa key to distinguishamong those species than to present a really comprehensivedescriptioncovering all important characters. Not all of the species listed fully meet the requirementsof a "sufficiently known species". Nevertheless, we are convinced that they actually exist as biological entities. The truenumberof species may be lower, as ca. 10 species can be regarded as candidatesto be lumped into other widespreadpolymorphic species. (2) Several taxa otherwise recognized have been excluded from the treatmentas they are obvious ecomorphosesor extreme morphotypesof other well-known species. The numberof species in Potamogetonis generallyoverestimated.Estimatesof 90-120 species areunjustified or based on a narrowerspecies concept. We think that in the context of the species concept outlined above 69 is approximatelythe right order of magnitude to be expected worldwide for Potamogetonspecies. We do not believe thattoo many "question-markspecies" will prove to be taxa in their own right in the future.Three species may lie undescribedin herbaria(one from Madagascar,New Guinea, and South America respectively). The question marks in the synonym lists, and in particularthe notes, show that there is a lot of work to be done in Potamogeton taxonomy,which has been hamperedby the fact that authenticseed materialfrom many partsof the world is difficult to obtain.Furthermore,many species are not easy to keep in cultivation and show only minimal development of morphologicalcharacters.Necessary work includes: (1) Extensive field surveys and collection of specimens in the Southern Hemisphere in orderto bringthe total numbersof specimens comparableto thatin the NorthernHemisphere. (2) Typification of all relevant names. "Relevant" refers to all species and hybrids recognized here, all taxa contributingbasionyms, and all taxa being importantfor applying the priorityrule. Taxonomy of Potamogeton 309 (3) Chromosomecounts on well identified specimens, both from the NorthernHemisphere but in particularfrom the SouthernHemisphere. (4) Experimentalcultivation in order to reveal the actual range of phenotypic plasticity. (5) Crossing experiments to verify or rule out assumed hybridization. (6) Molecular approacheson the affinity of species and species groups as well as on the verification of hybrids. Acknowledgements:We thankthe keepersof all herbariawho contributedloansto this studyor who allowed us to work in their institutions.K. van de Weyer(Nettetal)communicatedimportantinformationon some CentralEuropeantaxa and S.E. Papassotiriou(Sydney)on some Australianones. K. Kubitzki(Hamburg) J. Stepanek criticallyreada preliminaryversionof the text.We arealso gratefulto C.D. Preston(Huntingdon), (Pruhonice)andC.D.K.Cook (Zurich)for reviewingandcommentingon the manuscript.Z. Kaplanhasbeen financiallysupportedby grantno. 206/98/1539of the GrantAgency of the CzechRepublic. REFERENCES AALTOM. (1970): Potamogetonaceae fruits. 1. Recent and subfossil endocarps of the Fennoscandian species. Acta Bot. Fenn. 88: 1-85. ASTONH.I. (1973): Aquatic plants of Australia. Melbourne University Press, Melbourne. BRux H., HElM R. & WIEGLEBG. (1989): Untersuchungen zum Lebenszyklus von Potamogeton alpinus BALBISund P natans L. Verh. Ges. Okol. 18: 665-670. DANDYJ.E. (1937): The genus Potamogeton L. in tropical Africa. J. Linn. Soc. Bot. 50: 507-540. DENNYP. & LYE K.A. (1973): The Potamogeton schweinfurthii complex in Uganda. Kew Bull. 28: 117-120. FERNALDM.L. (1932): The linear-leaved North American species of Potamogeton section Axillares. Mem. Amer Acad. Arts, N. Ser 17: 1-183. GRAEBNER P. (1907): 4. Potamogeton (TOURN.)L. In: ENGLERA. (ed.), Das Pflanzenreich, Regni vegetabilis conspectus 31 (VI. II), Berlin, pp. 39-142, 161-162. HAGSTROM J.O. (1908): New Potamogetons. Bot. Not. 1908: 97-108. HAGSTROM J.O. (1916): Critical researches on the Potamogetons. Kungl. Svenska Vetenskapsakad.Handl. 55(5): 1-281. HAYNESR.R. (1974): A revision of North American Potamogeton subsection Pusilli (Potamogetonaceae). Rhodora 76: 564-649. HAYNESR.R. (1985): A revision of the clasping-leaved Potamogeton (Potamogetonaceae). Sida 11: 173-188. HELLQUIST C.B. (1978): Potamogeton gramineus with adnate stipules. Rhodora 80: 591-593. HOLLINGSWORTH P.M., PRESTON C.D. & GORNALL R.J. (1996): Genetic variability in two hydrophilous species of Potamogeton, P. pectinatus and P filiformis (Potamogetonaceae). Pl. Syst. Evol. 202: 233-254. HOLLINGSWORTH P.H., PRESTONC.D. & GORNALLR.J. (1998): Euploid and aneuploid evolution in Potamogeton (Potamogetonaceae): a factual basis for interpetation. Aquat. Bot. 60: 337-358. HOLUBJ. (1997): Stuckenia BORNER1912 - the correct name for Coleogeton (Potamogetonaceae). Preslia 69: 361-366. KADONOY. & WIEGLEBG. (1987): Two new Potamogeton hybrids from Japan. J. Jap. Bot. 62: 80-84. KAPLANZ. (1995): Genus Potamogeton on the Svjatoj Nos isthmus and in the Barguzinskaja valley, Lake Baikal. Siberian Naturalist (Praha) 1: 73-89. KAPLANZ. (1997): New names of Potamogeton published by Bohemian botanists. Preslia 69: 193-239. KAPLANZ. (1998): (1364) Proposal to conserve the name Potamogeton maackianus (Potamogetonaceae) against P serrulatus. Taxon 47: 735-736. KASHINAL.I. [= KASCHINA L.I.] (1988): Semeistvo 24. Potamogetonaceae - Rdestovye. In: KRASNOBOROV I.M. (ed.), Flora Sibiri, Lycopodiaceae - Hydrocharitaceae, Nauka, Novosibirsk, p. 93-105, 165-176. LEACHG.J. & OSBORNEP.L. (1985): Freshwater plants of Papua New Guinea. The University of Papua New Guinea Press, Port Moresby. LESD.H. (1982): Taxonomic implications of aneuploidy and polyploidy in Potamogeton (Potamogetonaceae). Rhodora 85: 301-323. LES D.H. & HAYNESR.R. (1996): Coleogeton (Potamogetonaceae), a new genus of pondweeds. Novon 6: 389-391. 310 G. Wiegleb & Z. Kaplan LESD.H. & SHERIDAN D.J. (1990a):Biochemicalheterophyllyand flavonoidevolutionof NorthAmerican Potamogeton(Potamogetonaceae). Amer.J. Bot. 77: 453-465. LESD.H. & SHERIDAND.J. (1990b): Hagstrom'sconceptof phylogeneticrelationshipsin PotamogetonL. (Potamogetonaceae).Taxon39: 41-58. MIKIS. (1937): The waterphanerogamsin Japanwith specialreferenceto those of the provinceYamashiro. Reportson the historicalremains,scenic places and naturalmonumentsin KyotoPref 18: 1-127. [in Japanese] OBERMEYER A.A. (1966): Potamogetonaceae. In:CODDL.E., DE WINTER B. & RYCROFT H.B. (eds.), Flora of SouthAfrica1, CapeandTransvaalPrintersLtd.,CapeTown,pp. 60-70. OGDENE.C. (1943): The broad-leavedspecies of Potamogeton.Rhodora45: 57-105, 119-163, 171-214. PRESTON C.D. (1995): Pondweedsof GreatBritainand Ireland.BSBI Handbookno. 8, BSBI, London. RAUNKIAER C. (1896): De DanskeBlomsterplanters Naturhistorie.1(1). Copenhagen. RAUNKIAER C. (1903):AnatomicalPotamogeton-studies andPotamogetonfluitans. Bot. Tidssk.25: 253-280. REZNICEK A.A. & BOBBETTE R.S.W.(1976): The taxonomyof PotamogetonsubsectionHybridiin North America.Rhodora78: 650-673. SORSAP. (1988):Pollenmorphologyof PotamogetonandGroenlandia andits taxonomic (Potamogetonaceae) significance.ActaBot. Fenn. 25: 179-199. SYMOENS J.J., VAN DE VELDEN J. & BUESCHER P. (1979): Contribution a l'6tudede la taxonomieet de la distributionde Potamogeton nodosus POIR. and Potamogeton thunbergii CHAM. & SCHLECHTEND. en Afrique. Bull. Soc. Roy. Bot. Belgigue 112 : 79-95. TOMLINSONP. (1982):VII.Helobiae (Alismatidae). In:METCALFEC.R.(ed.),Anatomy of the monocotyledons. ClarendonPress,Oxford,pp. 270-335. N.N. (1987): Sem. 136. Rdestovye - PotamogetonaceaeDUMORT.In: TZVELEV KHARKEVICH S.S. [= CHARKEVICZS.S.] (ed.), Sosudistye rasteniya sovetskogo Dal'nego Vostoka[Plantae vasculares Orientis extremi Sovietici] 2, Nauka, Leningrad, pp. 317-335. TUR N. M. (1982): Revisiondel generoPotamogetonL. en la Argentina.Darwiniana24: 217-266. VOLOBAEVP. (1993): Zametkao Potamogeton henningii A. BENN. (Potamogetonaceae) v Sibiri (Nota de speciePotamogeton henningii A. BENN.(Potamogetonaceae) in Sibiria).Novosti Sist. Vyssh.Rast. 29: 5-8. WIEGLEB G. (1988):Notes on pondweeds- outlinesfor a monographical treatmentof the genusPotamogeton L. Feddes Repert. 99: 249-266. WIEGLEBG. (1 990a): A redescription of Potamogeton distinctus (Potamogetonaceae) including remarks on the taxonomic structure of the P. nodosus group. Pl. Syst. Evol. 169: 245-259. WIEGLEB G. (1 990b): A redescription of Potamogeton wrightii (Potamogetonaceae). Pl. Syst. Evol. 170: 53-70. WIEGLEB G. (1990c): The importanceof stem anatomicalcharactersfor the systematicsof the genus Potamogeton L. Flora 184: 197-208. WIEGLEBG. (1993): Two new species of the genus Potamogeton L. (Potamogetonaceae) from Papua-New Guineaandthe SolomonIslands.Blumea37: 379-384. WIEGLEB G. & BRUX H. (1991): Comparisonof life-historycharactersof broad-leavedspecies of the genus PotamogetonL. I. Generalcharacterization of morphologyand reproductivestrategies.Aquat.Bot. 39: 131-146. WIEGLEB G. & KADONOY. (1989a): Growthand developmentof Potamogeton malaianus in Southwestern Japan. Nordic J. Bot. 9: 167-178. WIEGLEB G. & KADONO Y. (1989b):Growthanddevelopmentof Potamogetondistinctusin an irrigationpond in SouthwesternJapan.NordicJ. Bot. 9: 241-249. YUZEPCHUKS.V. [= JUZEPCZUK S.V.] (1934): Sem. XVII. Rdestovyje - Potamogetonaceae ENGL. In: KOMAROV V.L.(ed.), Flora SSSR[Flora URSS]1, Leningrad,pp. 224-265. Received3 June 1998, revisionreceivedandaccepted11 September1998 EnCl.Appendixpp. 311-316 311 Taxonomy of Potamogeton APPENDIX Index of scientific names Only final epithetswith authorshipare includedinto the index. Nomenclaturalsynonymswith the same final epithetare representedby theirbasionymonly.Epithetsof correctnames(or theirbasionyms)of acceptedspecies areprintedin bold. Supraspecific names ColeogetonRCHB. GroenlandiaJ. GAY. Potamogeton L. StuckeniaBORNER 243, 244 243 241-245, 247, 259, 270, 283, 308 243-244 Specific and infraspecific names in Potamogeton acifolius Y.C.MA 307 acuminatus FIEBER 292 acuminatus SCHUMACH. 274 acuminatus WAHLENB. 279 acutifolius FIEBER 284 acutifolius LINK 243, 250, 287, 288, 292-293 acutus SCHLTDL. 291 affinis A. BENN. 275 256 affinis BOENN.ex CHAM.et SCHLTDL. alatofructus A. BENN. 278 alatus KoIDZ. 268 alpinonatans F.W. SCHULTZ 256 alpinus BALB. 242, 243, 247, 248, 253, 256, 263, 264, 274, 277, 278, 280, 285 alpinus BLYTT 304 amblyphyllus C.A. MEY. 249, 305 americanus A. BENN. 289 americanus CHAM.et SCHLTDL 269 amphibius FR. 274 amphibius HAGSTR. 260 amplifolius TucK. 248, 254, 261 anadyrensis V.N. VASSIL. 290 anglicus HAGSTR. 256 anguillanus KOIDZ. 278 angustifolius FIEBER 297 angustifolius G. MEY. 266 angustifolius GRAEBN. 279 angustifolius J. PRESL 245, 274, 275, 277, 289 angustissimus HAGSTR. 273 angustissimus KUNTH 306 annulatus BELLARDI 263 antaicus HAGSTR. 292 apertus MIKI 293, 299 apicalis HAGSTR. 262 applanatus Y.D. CHEN 304 argentinus A. BENN 292 aschersonii A. BENN. 292 asiaticus A. BENN. 298 atripes FERNALD 301 attenuatus A. CAMUS 268 attenuatus HAGSTR. 286, 293 augustanus BALB. aulacophyllus K. SCHUM. australiensis A. BENN. australis F. PHIL. australis KIRK ex A. BENN. austriacus GAND, austrosibiricus KASCHINA azoricus A. BENN. baagoei 306 285, 298 FRYER 292, 294 275 292, 294 243, 250, 302 FERNALD 276 276 258, 277 FRYER 277, 286 279 304 HAGSTR. brasiliensis A. BENN. ex GRAEBN. brevifolius CELAK. bunyonyiensis DENNY et LYE bupleuroides FERNALD burkartii HORN ex TUR DANDY 273 292 biwaensis MIKI borealis LAEST. borealis RAF. cadburyae 304 297 biformis HAGSTR. biformoides PAPCHENKOV bottnicus 284 261 berchtoldii FIEBER berolinensis ASCH. et GRAEBN. berteroanus PHIL. billupsii 307 282 275 babingtonii A. BENN. badioviridis HAGSTR. badius HAGSTR. baenitzii GAND. balatonicus GAMS bicupulatus 304 254, 258, 259, 283 264 A. BENN. bennettii 276 et G. TAYLOR californicus MORONG canadensis HAGSTR. canariensis LINK capensis CHAM. ex KUNTH capensis SCHEELE ex A. BENN. capensis SCHEELE ex HAGSTR. capensis T. DURAND et SCHINZ capillaceus POIR. capillaris GAUDIN 303, 307 272 279 265 278 294 275, 285 295 302 269 264 273 273 264 301 297 G. Wiegleb & Z. Kaplan 312 capitatusENGELM. carinatusKUPFFER caspary KOHTS caudatusSEIDLex OPIZ 301 288 263 274 cayugensis WIEGAND cespitosus NOLTE ex RCHB. chakassiensis KASCHINA chamissoi A. BENN. champlainii A. BENN. 280 A. BENN. cheesemanii 294 307 273, 274 270 253, 257, 259, 260, 282, 283, 284 chongyangensisW.X. WANG 290 claytonii TUCK. clystocarpus FERNALD cognatus AsCH. et GRAEBN. coloratus HORNEM. 280 293, 294 278, 280 254, 257, 258, 277, 293 columbianus SUKSDORF complanatus WILLD. compressus L. 306 288 250, 251, 288, 289-291 condylocarpus TAUSCH confervoides 297 251, 300 RCHB. conjungens HAGSTR. connecticutensis J.W. ROBBINS cooperi FRYER cordatolanceolatus MERT. et W.D.J. KOCH ex FIEBER coriaceus FRYER coriaceus MERT. et W.D.J. KOCH corniculatus G. MEY. cornutus J. PRESL et C. PRESL L. 278, 285 277 275 274 279 274 crassifolius FRYER crenulatus D. DON crispatus WALLMAN ex FR. crispus 301 272 266 284 284 243, 248, 250, 264, 275, 278, 280, 284, 285, 291,298 cristatus REGEL et MAACK distinctus A. BENN. 242, 243, 255, 257, 259, 267, 268, 269, 271 243, 250, 301, 302 diversifoliusRAF. 270 drucei FRYER 253, 282, 283 drummondiiBENTH. 306 drupaceus0. LANG 292 dualis HAGSTR. 267 dubiusTIsELIus 272, 273 dunicolaTUR 291 elongatusWAHLENB. 252, 280, 281, 282 epihydrusRAF. 298 ethiopicusLYE 292 exiguusHAGSTR. 276 falcatus FRYER 277 fallax AsCH. et GRAEBN. 304 fasciculatus WOLFG. 289, 291 fauriei A. BENN. 245, 270, 272 faxonii MORONG 303, 305 fennicus HAGSTR. 254, 262, 270 ferrugineus HAGSTR. 295 fibrillosus FERNALD 264 fibrosus HAGSTR. 249, 303, 304, 305, 307 fihiformisPERS. 277 fischeri ASCH. et GRAEBN. 306 flabellatus BAB. 279 flexuosus WREDOW 266, 267 floridanus SMALL 267 fluitans auct. 266, 267, 274, 289 fluitans ROTH 306 fluviatilis SCHUBL. et G. MARTENS 243, 251, 295, 296 foliosus RAF. 268 fontigenus Y.H. Guo et al. 272 fragillimus HAGSTR. 268 franchetii A. BENN. et BAAGOE ex A. BENN. friesii 251, 285, 288, 291, 292 RuPR. curtisii MORONG 295 frondosus HAGSTR. fryeri A. BENN. curvatus 272 furcatus 277 gaudichaudii CHAM. et SCHLTDL. 287 gayi A. BENN. 243. 252, 299 A. BENN. curvifolius HARTM. cuspidatus SCHRAD. ex MERT. et W.D.J. cymatodes ASCH. et GRAEBN. cymbifolius G. FIsCH. cyprifolius LOWE ex GRAEBN. danicus GAND. decipiens NOLTE ex W.D.J. KOCH delavayi A. BENN. deminutus HAGSTR. dentatus HAGSTR. denticulatus LINK dichotomus WALLR. KOCH HAGSTR. gemmifer 275 gemmiparus J.W. ROBBINS genuinus IELAK. genuinus FERNALD genuinus RCHB. 270 gessnacensis RCHB. G. FISCH. 292 306 gracilis A. BENN. ex GRAEBN. gracilis FR. gracilis KuzMIN et SKVORTZOV gracilis WOLFG. diffusus A. BENN. diffusus HAGSTR. 297 gramineus digynus WALLICH dimidius CREP. dimorphoides HAGSTR. dimorphus RAF. dissimilis A. BENN. distachyus BELLARDI 268 272, 277 274 L. 301 301 307 276 292, 294 292 295 284 256, 266 272 292 306 276 243, 253, 256, 258, 264, 267, 272, 274, 275, 277, 278, 286 306 291 274 284 279 256 250, 287 251, 294 279 297 283 254, 255, 260, 261 graminifolius FR. griffithii A. BENN. grisebachii HEUFF. groenlandicus HAGSTR. grovesii DANDY et G. TAYLOR harzii G. FISCH. 276 264, 280 292 293, 294 293, 298 266 Taxonomy of Potamogeton 313 harzii G. FISCH.ex GRAEBN. haynesii HELLQ.et G.E. CROW 289, heidenreichii ASCH. et GRAEBN. helodes DUMoRT. helveticus G. FISCH. henningii A. BENN. 287, henryi FERNALD heterophyllus FR. (underP gramineus) heterophyllus FR. (underP. lucens) heterophyllus G. MEY. heterophyllus SCHREB. hibernicus A. BENN. hibernicus HAGSTR. hillii MORONG 251, 289, hindostanicus HAGSTR. hoggarensis DANDY 293, hohenackeri GAND. homophyllus HAGSTR.(underP. amplifolius) homophyllus HAGSTR.(underP illinoensis) hornemanoniiG. MEY. hubeienisis W.X. WANG et al. huillensis WELW.ex SCHINZ hungaricus GAND. hybridus PETAGNA illinoensis MORONG 243,253,254,262,267,270, inbaensis KADONO indicus MIQ. indicus ROXB. insulanus HAGSTR. interior RYDB. intermixtus A. BENN. interruptus KIT. intortusifolius J.B. HE et al. intramongolicus Y.C. MA inivolutus FRYER iriomotensis MASAMUNE japonicus A. BENN. japonicus FRANCH. et SAV. javanicus HASSKARL jeholensis KITAGAWA johannis HESL.-HARR. juncifolius A. KERN. ex C. FRITSCH juzepczukii P. DOROF.et TZVELEV kamogawaensis MIKI kirkii SYME kirkii SYMEex HOOK.f. kochii F.W. SCHULTZ kochii 0. LANG kupfferi A. BENN. kyushuensis KADONOet WIEGLEB lactucaceus MONTANDON lacunatus HAGSTR. lacustris PEARSALL et PEARSALLf. lacustris WALLMAN lanceolatifolius TISELIUS lanceolatus J.W. ROBBINS lanceolatus POIR. 258, 293 266 295 275 257 306 288 291 276 275 lanceolatus SM. lanciformis ROEM. et SCHULT. latifolius J.W. ROBBINS 307 latifolius MORONG 299 276 latifolius SLOBODA 276 275 latior HOLUB 258 266 leptocephalus 296 271 294 leschenaultii CHAM. et SCHLTDL. lateralis 276 299 MORONG laticaulis WAHLENB. 288 latifolius FIEBER 297 306 291 latifolius G. MEY. (under P pectinatus) latifolius G. MEY. (under P pusillus) 307 279, 286 KOIDZ. 284 GAND. leptophyllus 269 298 HAGSTR. ligulatus limosellifolius 284 262 272 linguatus 257 livingstonei 298 298 284 loculosus loeselii 275 longifolius MAXIM. 298 ex KORSH. 254, 261, 270, 273 HAGSTR. 285, 291 lintonii FRYER liocarpus 297 ASCH. 306 A. BENN. 293 HAGSTR. 277 et SCHULT. ROEM. lonchites 276 TUCK. 274 J. GAY longiligulatus FERNALD 272,273,277 274 268 269 270 304 278 295 268 A. CAMUS 243, 247, 248, 254, 264, 266, 267, 271, 273, longipetiolatus lucens L. 274, 275, 277, 278, 285 lundii K. RICHT. 277 A. BENN. maackianus 243, 249, 271, 277, 279, 285, 286, 291 295 macellus FERNALD 306 macounii MORONG 271 macrocarpus 306 macrophylloides 277 299 285 270 298 271 264 macrophyllus WALLR. 274 macrophyllus WOLFG. 274 304 ex MACOUN 306 DOBROCHOT. 272 HAGSTR. 284 GAND. macrorrhynchus 264 A. BENN. macvicarii 304 HAGSTR. magellanicus major A. BENN. ex GRAEBN. 298 major FIEBER 287 304 277-279 major FR. 291 major MERT. et W.D.J. KOCH 292 291,299 267 267 256 malaianus auct. 271 276 275 286,291 malaianus 269, 271 MIQ. malainoides 269 MIKI manchuriensisA. BENN. (under P acutifolius) 251, 289, 290 mandschuriensis A. BENN. (under P perfoliatus) marianensis 269 CHAM. et SCHLTDL. 269 284 292 293 279 256,277 methyensis A. BENN. 279 mexicanus A. BENN. 276 microcarpus Boiss. et REUT. marinus 306 L. mascarensis maximus 278 CHAM. et SCHLTDL. MORONG ex A. BENN. membranaceus HAGSTR. 276 258 272 269 256 G. Wiegleb & Z. Kaplan 314 microstachys WOLFG. miduhikimo MAKINO miguelensis DANDY millardii HESL.-HARR. minor BIv. minor FIEBER minor HOOK. miyakezimensis HONDA mongolicus A. BENN. mongolicus MAXIM. ex A. BENN. moniliformis H. ST. JOHN monoginus MIKI monogynus J. GAY montanensis GAND. montanus C. PRESL montevidensis A. BENN. monticolus 263 298 257 293 292 287 289 271 306 276 302 288 297 263 261 252, 281, 282 SCHWEIN. ex A. BENN. ochreatus RAOUL octandrus POIR. 250, 287 243, 252, 267, 291, 293, 298, 299, 300 291 oederi G. MEY. ogdenii HELLQ. et R.. HILTON 245, 289, 296 266 olivaceus BAAGOE olivaceus BAAGOE ex G. FISCH. 264, 285 olivaceus 0. LANG 275 HAGSTR. 291, 293 orientalis 297 orthorrhynchus GAND. ovalifolius FIEBER 266 MERT. et W.D.J. KOCH ex FIEBER ovalifolius ovatifolius WALLR. 269, 270 CHAM. et SCHLTDL. owaihiensis 277 277 pallidior GAND. 250, 286, 289, 290, 291, 293, 299 284 DRUCE 263 oxyphyllus MIQ. 300 palmerii 266 paludosus BOENN. ex STEUD. 266 mucronatus C. PREESL mucronatus FIEBER 270 paludosus BORY ex CHAM. et SCHLTDL. 256 292 pamiricus BAAGOE mucronatus SCHRAD. ex RCHB. 291 panormitanus mucronatus SCHRAD. ex ROEM. et SCHULT. morongii A. BENN. 291 papuanicus mucronatus SCHRAD. ex SONDER 291 paramoanus muelleri 305 292 Biv. 244, 253, 268 WIEGLEB 281 R.R. HAYNES et HOLM-NIELS. 244, 255, 257, 265 HAGSTR. A. BENN. 278 parmatus multidenticulatus MORONG 301 parvifolius BUCHENAU 298 muricatus 259 pauciflorus PURSH 295 276 paucifolius OPIZ HAGSTR. myriophyllus mysticus J.W. ROBBINS 279, 293 MORONG nakamurai YAMAUCHI et MOMIY. natans L. 242-244, 270, nericius HAGSTR. 264, 277 nerviger WOLFG. 264, 274 WOLFG. niagarensis TUCK. nigrescens FR. nipponicus MAKINO nitens WEBER nodosus 243, 255, 259, 265-268, noltei G. FISCH. nomotoensis notarisii GAND. oakesianus J.W. ROBBINS VIv. oblongus obrutus A.W. obscurus WOOD obtusus peruvianus 277 perversus MERT. et W.D.J. 297 258 C. PRESL ex A. BENN. 269 268 A. BENN. petiolaris C. PRESL 269 269 WOLFG. petiolatus 297 274 phialae 307 philippinensis A. BENN. planifolius G. MEY. DUCROS ex ROEM. et SCHULT. plantagineus pleiophyllus HAGSTR. POST 284 polygonifolius 270 298 polygonus 280 porrectifolius porsildiorus 256 porteri 256 praelongus PouRR. A. BENN. ex GRAEBN. KOCH 251, 296, 297 SCHLTDL. occidentalis J.W. ROBBINS occidentalis SIEBER ex CHAM. et SCHLTDL. 257 267 250, 286, 293 272 290 FERNALD 296 FERNALD 248, 252, 264, 275, 278, 279, 280, 285 prolixus W.D.J. KOCH promontoricus HAGSTR. protensus WALLR. 304 prussicus HAGSTR. pseudofluitans SYME 269 pseudofriesii 296 284 283 HAGSTR. WULFEN 286 255, 256, 257, 264, 266, 277, 293 CHAM. et SCHLTDL. porrigens 282 284 280 277, 278-280, 292 263 obtusifolius FIEBER 275, HAGSTR. ex DRUCE 263 DC. obtusifolius 273, 285, 286, 293 276 243, 252, 267, 268 oblongifolius KIRK ex HOOK. f. oblongorufescens F.W. SCHULTZ 253, 264, 271, perpygmaeus 244, 245, 267, novaeboracensis MORONG numasakianus A. BENN. nuttallii CHAM. et SCHLTDL. L. perfoliatus 295 266 KADONO et T. NOGUCHI WILLD. ex CHAM. et SCHLTDL. pennsylvanicus perneglectus GAND. 269, 270-272, noltei A. BENN. 272 pedersenii TUR 264 245, 277, 278 POIR. 306-308 279 248, 252, 256, 265, 266-268, 274, 277, 293, 299, 307 nervigerus 276 242, 244, 248, 249, 267, 303, 305, L. pectinatus DANDY et G. TAYLOR 266 273 306 264, 278 256 288, 292 315 Taxonomy of Potamogeton pseudolucensHAGSTR. pseudopolygonusHAGSTR. pseudorutilusA. BENN. pseudoziziiHAGSTR. pulchelliformisHAGSTR. pulcher TucK. pumilusNUTT. ex A. BENN. 272 286 295 273 272 254, 260 285 pumilus WOLFG. punense GALAN-MERA purpurascens SEIDL ex J. PRESL et C. PRESL pusilliformis HAGSTR. L. pusiUus HAGSTR. 263 292 solomonensis 264 243, 253, 279 GILLOT 257, 293 robbinsii OAKES 243, 249, 285 rostratus HAGSTR. A. 304, 305 rutiloides rutilus BENN. sachalinensis 266 269 270 278 278 278 277 269 284 284 263 256 295 251, 294, 295 H. LEv. 277, 278 salicifolius auct. salicifolius 272 270 FERNALD WOLFG. WOLFG. 275 274, 275, 278 salignus FRYER samarifornis HAGSTR. 282, 283 sarmaticus 276, 277 275 MEMErS scheelei G. PREuss ex GRAEBN. schreberi G. FISCH. schweinfurthii A. BENN. 256 266, 270 254, 265, 273, 274, 278 sclerocarpus K. SCHUM. scoliophyllus HAGSTR. scoparius WALLR. seemenii ASCH. et GRAEBN. semicoloratus A. BENN. semipellucidus W.D.J. KOCHet ZIz serotinus SCHRAD. ex SCHULT. et SCHULT. f. serrulatus OPIZ serrulatus REGEL et MAACK 293 252, 254, 255, 270, 283, 284 spirillus 249, 303, 304 273 rugelii 274 266 298 rosulatus HAGSTR. rothii A. BENN. ex G. FIsCH. rothii G. FISCH. rotundatus HAGSTR. rotundifoliusMERT.et W.D.J. KOCHex FIEBER rotundifolius MERT.et W.D.J. KOCHex RCHB. rotundifolius SONDER rotundifolius WALLR. roxburghianus SCHULT. et SCHULT. f. rubricans GAND. rubrinaevus GAND. rufescens SCHRAD. ex CHAM. rufescentinatans F.W. SCHULTZ WIEGLEB 282, 283 280 279 repens HAGSTR. rivularis siculus sparganiifolius LAEST. ex FR. spathulaeformis J.W. ROBBINS spathulatus SCHRAD. ex W.D.J. KOCH et ZIz spicatus ENGELM. spirilliformis HAGSTR. 301 A. BENN. 304 251, 290 306 304 richardii SOLMS A. BENN. 257 reniacoensis SPARRE richardsonu SCHUMACH. 260 283 J. PRESL 242, 243, 248, 251, 257, 258, 267, 279, 286, 288, 291, 292, 293-299 recurvatus setaceus sibiricus 284 siculus TINEO ex Guss. similis A. BENN. sinicus MIGO skvortsovii KLINKOVA 280 pygmeus GALINIS quinquenervius HAGSTR. ramosus PECK raunkiaeri G. FISCH. serrulatus SCHRAD. ex RCHB. sessilifolius A. CAMUS sessilifolius HAGSTR. 281 262 306 276 275 267 249, 307, 308 251, 289, 295 A. BENN. A. BENN. tepperi tepperiauct. 284 thomasii A. BENN. A. BENN. thunbergii CHAM. et SCHLTDL. 263 268 258 298 293 277 261 249, 303 267 260 290 292 288, 289, 293 305, 307 254, 259, 260, 270, 283 sumatranus MIQ. syriacus CHAM. et SCHLTDL. tasmanicus HAGSTR. tataricus LESSING teganumensis MAKINO tennesseensis FERNALD tenuicaulis F. MUELL. tenuifolius F. PHIL. tenuifolius KUNTH tenuifolius RAF. tenuinervis A. CAMUS tenuior MIQ. tenuis WAHLENB. tenuissimus MERT. et W.D.J. KOCH 266 304, 305 255, 257, 259, 283 HAGSTR. 270 263 285, 286 270 244, 255, 257, 263 subobtusus HAGSTR. subretusus HAGSTR. subrufus HAGSTR. subsessilifolius A. CAMUS subsibiricus HAGSTR. subtrichoides SCHUR sudermanicus HAGSTR. suecicus K. RICHT. sukcatus 301 301, 302 262 strictus PHIL. stylatus HAGSTR. subcordatus A. CAMUS subflavus H. LORET et BARRANDON subfuscus A. BENN. subjavanicus HAGSTR. subnitens HAGSTR. suboblongus 272 256, 264 243, 250, 300 TUCK. spoliatus HAGSTR. stagnorus HAGSTR. stenostachys K. ScHuM. steriliformis HAGSTR. sterilis HAGSTR. striatus RuIz et PAV. strictifolius 267, 277 270, 271 269 283 296 274 280 298 292 306 263 286 268 296 292 254, 255, 259, 270 259 263 243, 255, 264, 265 G. Wiegleb & Z. Kaplan 316 tiselii K. RICHT. tonkinensis A. CAMUS torquatus KoIDZ. 267 271 260 torssanderi TISELIUS 275 tretocarpus MAXIM. ex A. BENN. 271 tricarinatus auct. 260, 283 tricarinatus F. MUELL. et A. BENN. (1892) 282 tricarinatus F. MUELL. ex A. BENN. (1887) 259 CHAM. et SCHLTDL. trichoides 242, 251, 285, 293, 297, 298 trichophyllus MORONG 302 WALLR. ex GRAEBN. tricostatus 301 trimmeri CASP. 297 trinervius 292 G. FISCH. et Guss. tuberculatus TEN. tuberculosus RCHB. 297 297 tuberosus ROXB. 284 tubulatus HAGSTR. 293 J.W. ROBBINS 300 turionifer HAGSTR. typicus FERNALD (underP epihydrus) tuckermanii 292 typicus FERNALD(underP strictifolius) 280 295 typicus OGDEN 277 ulei K. SCHUM. undulatus upsaliensis WOLFG. 252, 281, 282, 286 280, 285 TISELIUS 275 Specific and infraspecific names in other genera Hydrogeton heterophyllus LOUR. Spirillus tuckermanni J. GAY ex A. BENN. Zannichellia cochlosperma A. BRAUNex A. BENN. Zannichellia palustris var.gyrocarpa TRIMEN 298 300 300 300 292 uruguayensis A. BENN. et GRAEBN. 245, 273, 274, 278 vaginans BOJER ex A. BENN. 249, 302, 303-305, 307 vaginatus TURCZ. 306 vaillantii ROEM. et SCHULT. 276 varians MORONG ex FRYER 267, 293 variifolius THORE 243, 252, 299, 300 vaseyi J.W. ROBBINS 273 venosus A. BENN. 264 venustus BAAGOE 264 venustus BAAGOE ex A. BENN. 264 venustus BAAGOE ex HAGSTR. 274 volhynicus BESSER ex ROEM. et SCHULT. 275 vollmannii G. FISCH. 266 vulgaris CELAK. 265 vulgaris SCHUBL. et G. MARTENS 276 wolfgangii KIHLM. 242, 243, 253, 269, 270, 271, 274, wrightiiMORONG 278, 286 275 xinganensis Y.C. MA 267, 299 yamagataensis KADONOet WIEGLEB 274 ZiZiiMERT.et W.D.J. KOCH 275 zizii W.D.J. KOCHex ROTH 306 zosteraceus FR. 288 zosterifolius SCHUMACH. 251, 289, 295, 296 zosteriformis FERNALD 288 zosterophyllusDUMORT.