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..
Aquatic perennial herbs, with rootstocks, mucilage-coated stems, floating or immersed leaves, and solitary axillary flowers. Sepals 3, rarely 4. Petals 3, rarely 4. Stamens 3-18; anthers extrorse, the connective continuous with the filament. Carpels 2-18, distinct. Stigmas sessile or nearly so; ovules 2 or 3, orthotropous. Fruits indehiscent, coriaceous, separate. Seeds 1-3, borne on the dorsal suture; embryo at the base of fleshy endosperm; cotyledons fleshy; hypocotyl very short.
Two genera and about 5 species, widely distributed in fresh-water lakes and streams.
Leaves dissected, excepting the small floating ones; stamens 3-6.
Leaves peltate, entire, floating; stamens 12-18.