large genus of plants belonging to the family Compositae and containing about 600 species, nearly all American and found chiefly in tropical South America, the West Indies, and Mexico. They are mostly perennial herbs, but a few are annuals, and many of the tropical species are shrubby or treelike. Members of the genus typically bear large, showy clusters of purplish, pink, blue, or white flowers. Some species are found in the United States and Canada, among them boneset (E. perfoliatum), which grows to a height of 1.5 m (5 feet) and bears white flowers; and joe-pye weed (E. purpureum), which reaches 2.7 m (9 feet) and has purplish flowers. The white snakeroot (E. rugosum) is a poisonous herb common in the central and western United States. Cattle allowed to pasture on this plant may suffer muscular tremors and weakness, a disorder called trembles.