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..
Perennial or rarely annual herbs, mainly aquatic, with alternate or verticillate leaves, the submerged ones often pectinate-pinnatifid Flowers perfect, or monoecious, or dioecious, axillary, in interrupted spikes, solitary or clustered. Calyx-tube adnate to the ovary, its limb entire or 2-4-lobed. Petals small, 2-4, or none. Stamens 1-8 Ovary ovoid-oblong, or short-cylindric, 2-8-ribbed or winged, 1-4-celled; styles 1-4; stigmas papillose or plumose. Fruit a nutlet, or drupe, compressed, angular, ribbed or winged, indehiscent, of 2-4 1-seeded carpels. Endosperm fleshy; cotyledons minute.
Eight genera and about 100 species, of wide geographic distribution.
Stamen 1; ovary 1-celled.
Stamens 2-8; ovary 3-4-celled.
Fruit 3-angled or 4-angled.
Fruit of 4 carpels.