Description from Flora of China
Trees [or shrubs], armed by spinescent stipules and stipels. Leaves bipinnate, not sensitive to touch; rachis and pinnae usually with extra-floral nectaries; leaflets 1 [to several] pairs per pinna. Inflorescences pedunculate heads or corymbs aggregated in terminal or axillary panicles. Flowers uniform, bisexual, 5-merous. Calyx shortly toothed. Corolla gamopetalous, 5-lobed. Stamens numerous, united into a tube at base. Ovary solitary. Legume spirally contorted [or straight], in most species dark brown outside, reddish orange within, flat, dehiscing along both sutures. Seeds brown or blackish, obovoid or asymmetric; testa hard, with a pleurogram; funicle developed into an aril.
About 18 species: indigenous to tropical and subtropical regions of the Americas; one species (introduced) in China.