This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
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: