locust, in botany, any species of the genus Robinia, deciduous trees or shrubs of the family Leguminosae (pulse family) native to the United States and Mexico. The locusts have pendent clusters of flowers similar to the sweet pea; these are very fragrant in the black, or yellow, locust ( R. pseudoacacia ), which is the common locust, sometimes also called acacia, or false acacia. This species has been widely planted in the past for ornamental purposes, for erosion control, and for its useful wood, but the locust borer has killed it in many areas. Its heavy, hard, durable wood has been used extensively for treenails in shipbuilding, for fence posts, for turning, and for fuel. The shoots and bark of the black locust are poisonous. The honey locust belongs to a different genus of this family, as does the carob, which is thought to have been the biblical locust. Locust is classified in the division Magnoliophyta, class Magnoliopsida, order Rosales, family Leguminosae.
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