locust, (genus Robinia), genus of about 10 species of flowering trees and shrubs in the pea family (Fabaceae), occurring in eastern North America and Mexico. Several locust trees are cultivated as ornamentals, especially the black locust (Robinia pseudoacacia), often called false acacia, or yellow locust. A number of species are also useful for erosion control and as timber trees.
Locusts are deciduous and bear long compound leaves with up to 21 oblong leaflets. Many species are armed with thorns. The flowers are often showy and fragrant and hang in loose clusters. The fruits are long flattened legumes.
The honey locust (Gleditsia triacanthos), also of the pea family, is a North American tree commonly used as an ornamental and often found in hedges.