Description from Flora of China
Herbs, annual or perennial. Stems twining, prostrate, or suberect. Leaves pinnately 3-foliolate; stipules small, wartlike or inconspicuous; stipels present, deciduous. Racemes axillary; bracts and bracteoles minute, deciduous. Flowers purple-violet, rose, or whitish, solitary or 2-6 clustered at swollen nodes. Calyx campanulate, 2-lipped, upper lip larger, truncate or 2-lobed, lower lip small or minute, entire or 3-toothed. Corolla longer than calyx; petals shortly clawed; standard large, suborbicular, reflexed; wings narrow, falcate, sometimes slightly twisted, free; keel broader than wings, incurved, obtuse or beaked, beak inflexed or spirally twisted, shorter than standard. Stamens monadelphous; anthers uniform. Ovary shortly stipitate, many ovuled; style incurved, beardless. Legumes large, ligulate or linear-oblong to oblong, compressed or slightly turgid, with prominent rib along ventral suture and extra ribs parallel and close to it, dehiscent by twisting of valves. Seeds 10-15, elliptic or oblong; hilum linear.
About 50 species: distributed in tropical and subtropical regions; five species (two introduced) in China.
(Authors: Wu Delin (吴德邻 Wu Te-lin); Mats Thulin)