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Family :


Division :



Perennial or rarely annual, partially or completely submerged aquatic herbs, rarely floating, of fresh- or salt-water habitats, rooted to the substrate or sometimes free floating. Leaves basal, and often crowded, or cauline, usually sessile, linear or orbicular, with or without petioles, often more or less sheathing. Inflorescence a compact, usually few-flowered cyme in especially staminate flowers, or a single flower in pistillate flowers, collectively subtended by a bifid spathaceous bract. Flowers bisexual or more commonly unisexual, small and inconspicuous, actinomorphic or slightly irregular. Perianth commonly of 3 distinct, green sepals and 3 distinct white or coloured petals. Male flowers with stamens 3- many, anthers 2-celled, 1 or more rudimentary sterile ovaries (pistillodes) usually present, female flowers unipistillate, ovary inferior, unilocular, often with more or less partial partitions, style 1, usually divided into as many branches as placentae, ovules numerous on each placenta, anatropous or seldom orthotropous. Fruit berry-like, globose or linear, dry or fleshy, indehiscent, submerged. Seeds several to numerous, embryo straight.

Key to the Genus

Serial Key Reference
1a. Leaves all basal, stems short 2
1b. Leaves cauline, stems elongated 4
2a. Leaves linear, ribbonlike, sessile; fruit narrowly cylindric 3
2b. Leaves lanceolate to orbicular, usually petiolate Ottelia
3a. Stamens 3-9, ovary attenuate into a long, filiform beak; peduncle of female flower shorter Blyxa
3b. Stamens 1-3, ovary not as above; peduncle of female flower very long Vallisneria
4a. Leaves whorled Hydrilla
4b. Leaves alternate, opposite, or spirally arranged Nechamend