Description from Flora of China
Twining or erect herbs, often with hooked hairs. Stipules basifixed, persistent, not produced below point of insertion. Leaves pinnately 3-foliolate; stipels present. Racemes axillary, flowers at swollen nodes. Bracts and bracteoles persistent or deciduous. Calyx 2-lipped, upper pair of teeth connate, lower lip 3-toothed. Corolla yellow, white, red, or purple; petals clawed; standard suborbicular, reflexed, sometimes with appendages at base; wings obovate or oblong, adherent to keel; keel linear, beak long, spirally coiled through 1-5 turns. Stamens diadelphous. Style spirally coiled through at least 360°; stigma oblique. Legumes linear or oblong, subterete or compressed. Seeds 2 to many, oblong or reniform; hilum shortly linear, estrophiolate.
About 50 species: native to tropical America; three species (all introduced) in China.
(Authors: Wu Delin (吴德邻 Wu Te-lin); Mats Thulin)