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..
Pubescent herbs, or low shrubs, with alternate simple or digitately 3-foliolate leaves, and purple or purplish, solitary or racemed, irregular perfect flowers. Peduncles 2-bracted at or above the middle. Stipules wanting. Sepals 4 or 5, usually large, the outer one commonly wider than the others. Petals usually 5, smaller than the sepals, the 3 upper ones long-clawed, often united by their claws, or the middle one of the 3 wanting, the 2 lower ones reduced to suborbicular fleshy glands. Stamens 3 or 4, monadelphous, at least at the base; anther-sacs opening by a terminal pore. Ovary 1-celled, or partly 2-celled; ovules 2, collateral, anatro-pous, pendulous; style slender, acute or truncate. Fruit globose, or compressed, spiny, indehiscent, 1-seeded. Seed without endosperm; cotyledons fleshy.
The family consists of only the following genus, with about 20 species, distributed from the southern United States to Chile. It has often been included in the Polygalaceae, but its affinity to Cassia and related genera indicates that it should be placed next to the Caesalpiniaceae.