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..
Herbs, rarely shrubs or small trees in tropical regions, with alternate, or sometimes opposite or verticillate leaves; stipules none. Flowers racemose, spicate, or solitary and axillary. Pedicels generally 2-bracted at the base. Flowers perfect, irregular. Sepals 5, the two lateral ones (wings) large, colored, the others smaller. Petals 3 (or 5), hypogynous, more or less united into a tube, the lower one often crested. Stamens generally 8, united in 1 or 2 sets. Ovary 2-celled; style simple; stigma curved, dilated or lobed; ovules 1 in each cavity, anatropous. Fruit mainly capsular. Seeds generally caruncled, often hairy; embryo straight.
About 10 genera and perhaps 1000 species, widely distributed in temperate and tropical regions.