1. Hydrocharitaceae Juss.

    1. This family is accepted.

[NTK]

Haigh, A. (2009). Neotropical Hydrocharitaceae.

Morphology
Description

Habit : aquatic herbs, sometimes emergent, stems stoloniferous or erect , corms often present when stems stoloniferous. 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.). 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. 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. Fruits berry -like, dehiscing irregularly or breaking up at maturity. Seeds 3-numerous, ellipsoid to cylindric or fusiform .

General Description
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.
Number of genera

See above

Status
  • Native. Two species Hydrillaverticilata and Najasgraminea are naturalised.
General notes
  • 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.
Distribution
Distribution in the Neotropics

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.
Diagnostic
Distinguishing characters (always present)
  • Aquatic herbs.
  • Leaves basal, alternate, opposite, or whorled, simple; basalsheath present.
Other important characters
  • Fruits berry -like.
  • Sepals and petals usually 3.
  • Ovary inferior.
  • Inflorescences subtended by 1-2 bracts.
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.
Literature
Important literature

Cook, C.D.K., 1998. Hydrocharitaceae. In: K. Kubitzki (ed.), The families and genera of vascular plants 4: 234-248. Springer Verlag, Berlin.

Haynes, R.R., 2004. Hydrocharitaceae. Pp. 444-446. In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D.W. & Heald, S.V. (eds.). Flowering Plants of the Neotropics. New York Botanical Garden, Princeton University Press, Princeton.

[FTEA]

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

Habit
Monoecious, dioecious or hermaphrodite, submerged or rarely floating, freshwater or marine, annual or perennial herbs
Roots
Roots mostly simple, adventitious, rarely with root hairs
Stem
Stems corm-like or elongate, rhizomatous, stoloniferous or erect, simple or dichotomously branched
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
Stipules
Stipules rarely present
General
Nodal scales (squamulae intravaginales) often present, situated in leaf-axils
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
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
Fruits
Fruit a capsule, sometimes beaked from remains of the perianth-tube, dehiscent or opening by decay of the pericarp
Seeds
Seeds usually minute; embryo straight with inconspicuous or conspicuous plumule; endosperm 0
[FWTA]

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

Habit
Fresh-water or salt-water herbs, partly or wholly submerged; roots sometimes floating
Leaves
Leaves radical or cauline, alternate to whorled
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
Perianth
Perianth-segments free, 1-2-seriate, 3 in each series, the outer often green, valvate, the inner petaloid
Androecium
Stamens numerous to 2
Male
Male flowers with rudimentary ovary
Sterile Parts
Staminodes usually present in the female flower
Gynoecium
Ovules numerous Ovary inferior, 1-locular, with parietal placentas sometimes protruding nearly to the middle of the ovary
Fruits
Fruit rupturing irregularly
Seeds
Seeds numerous, without endosperm
[FWTA]

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

Habit
Small submerged annual water-plants; stem slender, much branched
Leaves
Leaves small, subopposite or verticillate, sessile, with a sheathing base and linear entire or toothed blade
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
Male
Male flower with 1 stamen; anther sessile, 1-4-locular
Inflorescences
Bract (spathe) of female flowers sometimes very thin and adhering to the carpel
Gynoecium
Ovule solitary erect Ovary of 1 carpel, 1-locular, with 2-4 stigmas
Fruits
Fruit usually embraced by the leaf-sheath, indehiscent
Seeds
Seed without endosperm
[FTEA]

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

Habit
Submerged annuals, more rarely perennials, in fresh to brackish waters, monoecious or dioecious
Roots
Roots simple, adventitious, devoid of root-caps
Stem
Stems rooting from the base and lower nodes, much branched, slender or robust, the internodes sometimes armed with spines (subgen. Najas)
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)
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
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
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
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
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

Images

Hydrocharitaceae Juss. appears in other Kew resources:

First published in Gen. Pl. [Jussieu] 67. 1789 [4 Aug 1789] (1789)

Accepted by

  • APG IV (2016) http://dx.doi.org/10.1111/boj.12385

Sources

Flora of Tropical East Africa
Flora of Tropical East Africa
http://creativecommons.org/licenses/by-nc-sa/3.0

Flora of West Tropical Africa
Flora of West Tropical Africa
http://creativecommons.org/licenses/by-nc-sa/3.0

Kew Names and Taxonomic Backbone
The International Plant Names Index and World Checklist of Selected Plant Families 2019. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
© Copyright 2017 International Plant Names Index and World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

Neotropikey
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