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 acaulescent herbs, with more or less elongated often tuber-bearing rootstocks. Leaves alternate: blades leathery or those of submersed leaves membranous and delicate, all with a sinus at the base, petioled. Flowers perfect, terminating elongated scapes. Sepals 4-6, often green. Petals numerous, usually passing into staminodia or stamens, decaying. Androecium of numerous stamens. Anthers introrse, adnate. Gynoecium of several or many carpels united into a compound ovary. Stigmas united into a disk with radiating stigmatic lines.
Ovules very numerous on the walls of the ovary. Fruit a leathery several-seeded berry. Seeds often shining, with the embryo enclosed in a sac at the base of the fleshy endosperm.
Five genera and about 45 species, widely distributed in fresh water.
Petals small or minute; stamens hypogynous.
Petals large, numerous; stamens epigynous.