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..
Low herbs, sometimes woody in tropical regions, with opposite or verticillate stipulate entire or serrate leaves, and small axillary solitary or fascicled flowers. Flowers regular, perfect. Sepals 2-5, imbricated. Petals the same number, hypogynous. Stamens the same number or twice as many. Ovary 2-5-celled; styles 2-5, stigmatic at the apex; ovules ∞, anatropous. Capsule with septicidal dehiscence. Placentae central. Seed-coat crustaceous, rugose or ribbed.
About 30 species, of wide geographic distribution.
Flowers 2-4-merous; glabrous aquatic or creeping herbs.
Flowers mainly 5-merous; pubescent ascending or diffuse herbs.