Hydrocharitaceae Juss.

Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://creativecommons.org/licenses/by/3.0

Morphology General Habit

Habit : aquatic herbs, sometimes emergent, stems stoloniferous or erect, corms often present when stems stoloniferous

Morphology Leaves

Leaves basal, alternate, opposite or whorled simple, sessile or petiolate; basal sheath present, distinct from blade or petiole, tubular; blades linear or expanded; aerenchyma present in abaxial part of leaf (Hydrocharis L. and Limnobium Rich.)

Morphology Reproductive morphology Inflorescences

Inflorescences often complex, of 1-many flowers, sessile in leaf axils or terminal on long scapes, subtended by 1-2 bracts, the scapes occasionally with up to 10 longitudinal ridges or wings

Morphology Reproductive morphology Flowers

Flowers actinomorphic, bisexual (often cleistogamous) or unisexual (plants dioecious), sessile or pedicellate (staminate flowers) or mostly sessile (pistillate flowers), the pedicels often long and filiform in staminate flowers (the elongated hypanthium often gives impression of pedicel in pistillate flowers); perianth often fused to form hypanthium; sepals (2)3; petals (absent or 2)3; androecium of 12-13 stamens (when present), the stamens in several whorls of mostly 3, the filaments distinct or united, the anthers basifixed or dorsifixed; gynoecium syncarpous, the ovary inferior (if present), the carpels 3-20+, the locules 1 or falsely 6-9, the styles 1-9, sometimes bifid, the stigmas linear, dry, papillose; placentation laminar

Morphology Reproductive morphology Fruits

Fruits berry -like, dehiscing irregularly or breaking up at maturity

Morphology Reproductive morphology Seeds

Seeds 3-numerous, ellipsoid to cylindric or fusiform .

Note

Number of genera: See above Hydrocharitaceae occupy streams, rivers, lakes, bays and oceans. Two Neotropical genera are strictly marine (Halophila and Thalassia), the rest occupy freshwater habitats. Hydrocharitaceae are of limited economic use, except as aquarium plants. Their invasive nature, however, is more important. Notes on delimitation: Placed in the Alismatales, they appear to be most closely related to the Alismataceae and Limnocharitaceae. Here, following APG II, the previously separate Najadaceae has been included in the Hydrocharitaceae.

Diagnostic

Notable genera and distinguishing features: Najas is the largest genus in the Neotropics with 7 species, sometimes armed with prickles on internodes, leaf margins usually serrate to minutely serrulate. Distinguishing characters (always present): Aquatic herbs. Leaves basal, alternate, opposite, or whorled, simple; basalsheath present. Fruits berry -like. Sepals and petals usually 3. Ovary inferior. Inflorescences subtended by 1-2 bracts.

Distribution

Native. Two species Hydrillaverticilata and Najasgraminea are naturalised. A cosmopolitan family of 18 genera and c.115 species. 10 genera comprising 21 species occur in the Neotropics. Apalanthe Planchon:  monospecific (A. granatensis Kunth) Planchon in fresh waters of tropical South America. Egeria Planchon:  two species in subtropical and temperate fresh waters in South America (E. densa Planchon - almost cosmopolitan due to its invasive nature). Elodea Michx:  five species in the Americas, two of which are widespread in the fresh waters of the Andes and temperate South America. Halophila Thouars:  ca. 10 species in the warm marine areas of the world, 3 species are native to the Neotropics. Hydrilla Rich:  monospecific (Hydrilla verticillata (L.f.) Royle is native to the old world but an invasive and naturalized in the fresh waters of the Americas). Limnobium Rich.: 2 species in tropical and temperate American fresh waters, 1 of these in the Neotropics. Najas L: about 40 species in fresh waters worldwide, seven species are native to the Neotropics, and Najasgraminea Delile - naturalized. Ottelia Persson:  21 species of which one is native to the fresh waters of the Neotropics. Thalassia Banks ex König:  two species, one of which is native to the salt waters of the Caribbean. Vallisneria L: six species of which one is native to the Neotropical fresh waters.

Hydrocharitaceae, David Simpson. Flora of Tropical East Africa. 1989

Morphology General Habit

Monoecious, dioecious or hermaphrodite, submerged or rarely floating, freshwater or marine, annual or perennial herbs

Morphology Roots

Roots mostly simple, adventitious, rarely with root hairs

Morphology Stem

Stems corm-like or elongate, rhizomatous, stoloniferous or erect, simple or dichotomously branched

Morphology Leaves

Leaves radical, or spirally arranged, or in whorls along the stem, or distichous or rarely opposite, sessile or petiolate, sometimes sheathing at the base; venation parallel or only midrib present

Morphology Leaves Stipules

Stipules rarely present

Morphology General

Nodal scales (squamulae intravaginales) often present, situated in leaf-axils

Morphology Reproductive morphology Flowers

Flowers unisexual or bisexual, 1–many, mostly regular, arranged in a spathe, the spathe axillary, sessile or pedunculate and composed of 2 wholly or partly connate, rarely free, bracts

Morphology Reproductive morphology Flowers Perianth

Perianth segments 3 or 6, the latter differentiated into sepals and petals; sepals free, usually green or whitish, often reflexed; petals free, often showy, sometimes reflexed; stamens 2–many, in 1 or more whorls; anthers 2–4-thecous, basifixed, dorsally or latrorsely, rarely introrsely or extrorsely dehiscent; filaments filiform or flattened, linear or club-shaped in outline, rarely 0; staminodes often present in ? flowers, rarely so in ? flowers, in the latter the staminodes differentiated from the inner whorl of stamens; ovary inferior, composed of 2–15 connate carpels, 1(–3)-locular; placentation parietal, rarely basal; ovules few to many, anatropus or orthotropus; styles 2–15; stigmas 2–15, entire or 2-lobed Perianth-tube (hypanthium) often present in ? and hermaphrodite flowers, exerted from or near the apex of the ovary, usually extending to carry perianth to water surface

Morphology Reproductive morphology Fruits

Fruit a capsule, sometimes beaked from remains of the perianth-tube, dehiscent or opening by decay of the pericarp

Morphology Reproductive morphology Seeds

Seeds usually minute; embryo straight with inconspicuous or conspicuous plumule; endosperm 0

M. Thulin et al. Flora of Somalia, Vol. 1-4 [updated 2008] https://plants.jstor.org/collection/FLOS

Morphology General Habit

Annual or perennial herbaceous freshwater or marine aquatics

Morphology Leaves

Leaves in a basal rosette, whorled along the stem, distichous or rarely opposite, sometimes sheathing at the base

Morphology Reproductive morphology Inflorescences

Flowers unisexual or bisexual, regular, solitary, paired or in umbel-like groups, enclosed by 2 separate or fused spathal bracts

Morphology Reproductive morphology Flowers Tepal

Tepals 3 or 6, free, when 6 the outer may be sepaloid and the inner petaloid

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens 2–many, the innermost or outermost often sterile (staminodes); anthers 2-thecous, basifixed, longitudinally dehiscent

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary inferior, composed of (2–)3–6(–20) carpels, generally 1-celled; styles as many as the carpels; ovules few to many

Morphology Reproductive morphology Fruits

Fruit a fleshy and berry-like capsule, dehiscent or opening by decay of the pericarp

Morphology Reproductive morphology Seeds

Seeds small with straight embryo, without endosperm.

Distribution

Family of some 14 genera and over 130 species, cosmopolitan.

Hydrocharitaceae, F.N. Hepper. Flora of West Tropical Africa 3:1. 1968

Morphology General Habit

Fresh-water or salt-water herbs, partly or wholly submerged; roots sometimes floating

Morphology Leaves

Leaves radical or cauline, alternate to whorled

Morphology Reproductive morphology Flowers

Flowers hermaphrodite or unisexual, arranged in a tubular spathe or within two opposite bracts, females solitary; peduncle sometimes spirally twisted in fruit Male flowers with rudimentary ovary

Morphology Reproductive morphology Flowers Perianth

Perianth-segments free, 1-2-seriate, 3 in each series, the outer often green, valvate, the inner petaloid

Morphology Reproductive morphology Flowers Androecium

Stamens numerous to 2

sex Male

Male flowers with rudimentary ovary

Morphology Reproductive morphology Flowers Sterile Parts

Staminodes usually present in the female flower

Morphology Reproductive morphology Flowers Gynoecium

Ovules numerous Ovary inferior, 1-locular, with parietal placentas sometimes protruding nearly to the middle of the ovary

Morphology Reproductive morphology Fruits

Fruit rupturing irregularly

Morphology Reproductive morphology Seeds

Seeds numerous, without endosperm

George R. Proctor (2012). Flora of the Cayman Isands (Second Edition). Royal Botanic Gardens, Kew

Morphology General Habit

Aquatic herbs, floating or submerged, with short to elongate leafy stem

Morphology Leaves

Leaves linear or strap-shaped, sessile or stalked

Morphology Reproductive morphology Flowers

Flowers regular, unisexual or rarely perfect, usually solitary within a stalked, tubular, 2-lipped spathe or else subtended by 2 overlapping bracts. Calyx of 3 sepals; corolla of 3 thin petals or lacking

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens 3–12, with linear 2- celled anthers

Morphology Reproductive morphology Flowers Gynoecium Carpels

Carpels 3–15, united, the ovary 1–15-locular with numerous ovules; styles or stigmas as many as the ovary-locules

Morphology Reproductive morphology Fruits

Fruit a berry or capsule.

Distribution

A widely distributed marine and fresh-water family of about 17 genera and 130 species.

J. R. Timberlake, E. S. Martins (2009). Flora Zambesiaca, Vol 12 (part 2). Royal Botanic Gardens, Kew

Morphology General Habit

Annual or rarely perennial, aquatic, obligately submerged herbs of fresh or brackish waters, monoecious or dioecious, glabrous, bottom-rooted, but parts often becoming detached and then free-floating

Morphology Roots

Roots adventitious, simple, devoid of root caps

Morphology Stem

Stems slender or robust, usually richly-branched, rooting from the base and lower nodes, internodes sometimes armed with prickles (subgen. Najas)

Morphology Leaves

Leaves sessile, alternate, but mostly appearing to be subopposite or in pseudowhorls of 3–7, with an open basal sheath and a simple, linear blade; sheath folded, its basal part enclosing 2 tiny hyaline intravaginal scales, its upper part mostly serrulate or prickly-dentate; blade 1-nerved, sometimes dorsally armed with prickles on the midrib, margins bearing (0)4–74(185) teeth on each side, apex acute to acuminate

Morphology Reproductive morphology Flowers

Flowers submerged, inconspicuous, unisexual, solitary at the base of an axillary shoot or sometimes aggregated above, sessile or shortly pedicellate, naked or surrounded by 1 or 2 membranous envelopes

sex Male

Male flower consisting of a solitary anther, sessile or subsessile, surrounded by 1 or 2 envelopes; outer envelope (“spathe”) present and then toothed or lacerated at apex, or absent; inner envelope (“perianth”) adhering to the anther and ending in 2 lips at apex; pedicel at first short, elongating just before anthesis and pushing the anther through the spathe; anther 1- or 4- sporangiate, dehiscing apically

sex Female

Female flower consisting of a solitary ovary (“gynoecial wall”), subsessile, 1-locular, sometimes ± surrounded by a lobed or toothed spathe; ovule solitary, basal, subsessile, erect, anatropous, with 2 integuments; style short, cylindrical, with 2–3(4) linear, often unequal, sometimes barren stigmatic arms

Morphology Reproductive morphology Fruits

Fruit 1-seeded, achene-like, but not actually drying, the fleshy pericarp adhering closely to the seed and dehiscing by decay, thin and membranous when dried

Morphology Reproductive morphology Seeds

Seed elliptic-oblong to ovate, sometimes asymmetrical at apex or U- shaped, without endosperm; testa hard, pitted with areoles irregularly arranged or regularly arranged in longitudinal rows, the end walls often raised; embryo straight with large hypocotyl and radicle, plumule well developed, cotyledon terminal.

Distribution

A family with only 1 genus, Najas, found in temperate and tropical regions worldwide.

Najadaceae, F.N. Hepper. Flora of West Tropical Africa 3:1. 1968

Morphology General Habit

Small submerged annual water-plants; stem slender, much branched

Morphology Leaves

Leaves small, subopposite or verticillate, sessile, with a sheathing base and linear entire or toothed blade

Morphology Reproductive morphology Flowers

Flowers unisexual, monoecious or rarely dioecious, very small axillary, often enveloped in a bract (spathe) with 2-lobed apex Male flower with 1 stamen; anther sessile, 1-4-locular

sex Male

Male flower with 1 stamen; anther sessile, 1-4-locular

Morphology Reproductive morphology Inflorescences

Bract (spathe) of female flowers sometimes very thin and adhering to the carpel

Morphology Reproductive morphology Flowers Gynoecium

Ovule solitary erect Ovary of 1 carpel, 1-locular, with 2-4 stigmas

Morphology Reproductive morphology Fruits

Fruit usually embraced by the leaf-sheath, indehiscent

Morphology Reproductive morphology Seeds

Seed without endosperm

Najadaceae, L. Triest (Vrije Universiteit, Brussels). Flora of Tropical East Africa. 1989

Morphology General Habit

Submerged annuals, more rarely perennials, in fresh to brackish waters, monoecious or dioecious

Morphology Roots

Roots simple, adventitious, devoid of root-caps

Morphology Stem

Stems rooting from the base and lower nodes, much branched, slender or robust, the internodes sometimes armed with spines (subgen. Najas)

Morphology Leaves

Leaves in subopposite pairs and mainly arranged in pseudowhorls of 3-7, sessile, with an open folded basal sheath and a linear blade; blade 1-nerved, sometimes with spines on the midrib; margins serrulate with (0-)4-60(-185) spines on each side; apex acute to acuminate, with 1-3 spines on each side; sheath of the second leaf clasping the main branch; sheath of the first and third leaf clasping a side branch or a flower; sheath variously shaped, upper part mostly serrulate or spiny-dentate, basal part enclosing 2 tiny axillary intravaginal hyaline scales (prophylls)

Morphology Reproductive morphology Inflorescences

Inflorescence a solitary unisexual flower at the very base of an axillary shoot, sessile or shortly stalked, the ? often but the ? flower more rarely enclosed in a thin membranous spathe; spathe tapering to the top in ? flowers or constricted into a cylindrical neck halfway along the style in ? flowers; the edge of the neck mostly with some spine-cells

Morphology Reproductive morphology Flowers

Male flower consisting of a solitary almost sessile anther invested by a thin envelope (often named “involucre” or “perianth”) which is bilobed at its apex; peduncle short, elongating at anthesis, pushing the flower through the envelope; anther uni- or tetrasporangiate, dehiscing irregularly; pollination hydrogamous; pollen globose to ellipsoid, monocolpate, 3-celled, the wall with shallow reticulations, thin, without exine, containing starch granules Female flower consisting solely of an ovary; ovary subsessile, ovoid, unicarpellate, 1-locular, 1-ovulate; ovule subsessile, erect, anatropous; ovary-wall 2 cell-layers thick, ending in a short cylindrical style with 2-3(-4) linear, often unequal stigmatic branches

sex Male

Male flower consisting of a solitary almost sessile anther invested by a thin envelope (often named “involucre” or “perianth”) which is bilobed at its apex; peduncle short, elongating at anthesis, pushing the flower through the envelope; anther uni- or tetrasporangiate, dehiscing irregularly; pollination hydrogamous; pollen globose to ellipsoid, monocolpate, 3-celled, the wall with shallow reticulations, thin, without exine, containing starch granules

sex Female

Female flower consisting solely of an ovary; ovary subsessile, ovoid, unicarpellate, 1-locular, 1-ovulate; ovule subsessile, erect, anatropous; ovary-wall 2 cell-layers thick, ending in a short cylindrical style with 2-3(-4) linear, often unequal stigmatic branches

Morphology Reproductive morphology Fruits

Fruit a 1-seeded nutlet (achene); pericarp very thin, closely enveloping the seed, part of the style and surrounding spathe (if any) persistent Seed elliptic-oblong to ovate, occasionally asymmetrical at apex, somewhat recurved or U-shaped, with a basal raphe and a distinctly areolated testa; testa hard, brittle, 3 or more cell-layers thick, pitted; areoles formed by the 2 outer layers of the testa, variously shaped, irregularly arranged in longitudinal rows of (9-)25-60(-100), the end walls sometimes raised; embryo straight; hypocotyl and radicle large; plumule well developed; cotyledon terminal, blunt; endosperm absent