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Family :


Division :



Perennial or rarely annual, partially or completely submerged aquatic herbs, rarely floating, of fresh-or salt-water habitats. Leaves basal, or cauline, usually sessile, linear or orbicular, with or without petioles, often more or less sheathing. Inflorescence a cyme in especially staminate flowers, or a single flower in pistillate flowers, bracteates. Flowers bisexual or more commonly unisexual, small and inconspicuous. Perianth of 3 sepals and 3 white or coloured petals. Male flowers: stamens 3-many, anthers 2-celled. Female flowers: unipistillate, ovary inferior, unilocular, style 1, ovules numerous. Fruits 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, ribbon-like, sessile. Fruit narrowly cylindric 3
2b. Leaves lanceolate to orbicular, usually petiolate Ottelia
3a. Peduncle of female flower very short; ovary attenuate into a long, filiform beak; stamens 3-9 Blyxa
3b. Peduncle of female flower very long; ovary not as above; stamens 1-3 Vallisneria
4a. Leaves whorled Hydrilla
4b. Leaves alternate, opposite, or spirally arranged Nechamandra