Hydrocharitaceae is a flowering plant family which includes 14 accepted genera and a total of ca 135 known species (Christenhusz & Byng 2016). The family holds a number of species of aquatic plants, including tape-grass, the well-known Canadian waterweed, and frogbit.
The family includes both freshwater and marine aquatics. They are found throughout the world in a wide variety of habitats, but are primarily tropical.
Description The species are annual or perennial, with a creeping monopodial rhizome with the leaves arranged in two vertical rows, or an erect main shoot with roots at the base and spirally arranged or whorled leaves. The leaves are simple and usually found submerged, though they may be found floating or partially emerse. As with many aquatics they can be quite variable in shape – from linear to orbicular, with or without a petiole, and with or without a sheathing base.
The flowers are arranged in a forked, spathe-like bract or between two opposite bracts. They are usually irregular, though in some case they may be slightly irregular, and either bisexual or unisexual. The perianth segments are in 1 or 2 series of 2–3 free segments; the inner series when present are usually showy and petal-like. Stamens 1–numerous, in 1 or more series; the inner ones sometimes sterile. pollen grains are globular and free but in the marine genera (Thalassia and Halophila) – the pollen grains are carried in chains, like strings of beads. The ovary is inferior with 2–15 united carpels containing a single locule with numerous ovules on parietal placentas which either protrude nearly to the centre of the ovary or are incompletely developed. Fruits are globular to linear, dry or pulpy, dehiscent or more usually indehiscent and opening by decay of the pericarp. Seeds are normally numerous with straight embryos and no endosperm.
Pollination can be extremely specialised.
The most recent phylogenetic treatment of the family recognizes four subfamilies. Subfamily Anacharioideae (Appertiella, Blyxa, Egeria, Elodea, Lagarosiphon and Ottelia) Subfamily Hydrilloideae (Enhalus, Halophila, Hydrilla, Maidenia, Najas, Nechamandra, Thalassia and Vallisneria). Subfamily Hydrocharitoideae (Hydrocharis, Limnobium) Subfamily Stratiotoideae (Stratiotes)
Uses Some species have become established ornamental plants, and subsequently serious weeds in the wild (especially Egeria, Elodea and Hydrilla).
Genera 14 genera are currently accepted.
Appertiella Blyxa Elodea (synonyms Apalanthe and Egeria ) Enhalus Halophila Hydrilla Hydrocharis (synonym Limnobium ) Lagarosiphon Najas Genera of Hydrocharitaceae, GRIN Taxonomy for Plants Nechamandra Ottelia Stratiotes Thalassia Vallisneria (synonym Maidenia )
+ Genera crosses (Hydrocharitaceae) Kubitzki (ed. 1998Kubitzki (ed.) 1998. The families and genera of vascular plants, vol 4, Monocotyledons: Alismatanae and Commelinanae (except Gramineae). Springer-Verlag, Berlin.) data.kewVascular Plant Families and Genera. List of genera in family HYDROCHARITACEAE (accessed 2016-06-02) http://data.kew.org/cgi-bin/vpfg1992/genlist.pl?HYDROCHARITACEAE APWeb (mobot.org)VASCULAR PLANT FAMILIES and GENERA. List of Genera in HYDROCHARITACEAE. (accessed 2016-06-02) http://www.mobot.org/mobot/research/apweb/genera/hydrocharitaceaegen.html Watson & Dallwitz (delta-intkey)Watson & Dallwitz. Hydrocharitaceae. The families of flowering plants. http://delta-intkey.com/angio/www/hydrocha.htm Hydrocharitaceae 1. Ottelia Ottelia Pers. (including Beneditaea Toledo, Boottia Wall.) (excludes Oligolobos Gagnep.) Ottelia Persoon (including Beneditaea Toledo, Boottia Wallich, Oligolobos Gagnepain, Xystrolobos Gagnepain) Ottelia 2. Stratiotes Stratiotes L. Stratiotes L. Stratiotes 3. Hydrocharis Hydrocharis L. Hydrocharis L. Hydrocharis 4. Limnobium Limnobium Rich. (including Hydromystria G.Mey. Limnobium Richard (including Hydromystria G. Meyer) Limnobium 5. Blyxa Blyxa Noronha ex Thouars (excludes Enhydrias Ridl.) Blyxa Richard (including Enhydrias Ridley) Blyxa 6. Apalanthe Apalanthe Planch. (in Elodea Michaux) Apalanthe 7. Egeria Egeria Planch. Egeria Planchon Egeria 8. Elodea Elodea Michx. (including Anacharis Rich., Udora Nutt.) Elodea Michaux (including Anacharis Richard, Apalanthe Planchon, Hydora Besser, Philotria Rafinesque, Serpicula Pursh, Udora Nuttall) Elodea 9. Hydrilla Hydrilla Rich. Hydrilla Richard Hydrilla 10. Appertiella Appertiella C.D.K.Cook & Triest Appertiella C. D. K. Cook & Triest Appertiella 11. Lagarosiphon Lagarosiphon Harv. Lagarosiphon Harvey Lagarosiphon 12. Nechamandra Nechamandra Planch. Nechamandra Planchon Nechamandra 13. Maidenia Maidenia Rendle Maidenia Rendle Maidenia 14. Vallisneria Vallisneria L. Vallisneria L. Vallisneria 15. Enhalus Enhalus Rich. Enhalus Richard Enhalus 16. Thalassia Thalassia Banks ex C.Koenig Thalassia C. Koenig Thalassia 17. Halophila Halophila Thouars Halophila Thouars Halophila (in Najas, Najadaceae) Najas L. Najas L. (in Najas, Najadaceae) (name not found) Enhydrias Ridl. (in Blyxa, Hydrocharitaceae) (name not found) (name not found) Oligolobos Gagnep. (in Ottelia, Hydrocharitaceae) (name not found) Najadaceae 1. Najas (in Najas, Hydrocharitaceae) (in Najas, Hydrocharitaceae) Najas
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