Herbaceous aquatic or rarely terrestrial plants, with slender or capillary stems, opposite exstipulate entire spatulateor linear leaves, and minute perfect or monoecious axillary flowers. Perianth none. Bracts 2, sac-like or none. Stamen 1; filament elongated, filiform; anthers cordate, 2-celled, opening by lateral slits. Pistil 1; ovary 4-celled; ovules I in each cavity; styles 2, filiform, papillose nearly the whole length. Fruit compressed, lobed, the lobes more or less winged or keeled on the margins, separating at maturity into 4 flatfish I-seeded carpels. Seed anatropous, pendulous; endosperm fleshy; embryo straight or slightly curved, nearly as long as the endosperm.

Consists of the following genus: