Description from Flora of China
Annual or perennial herbs, rarely shrubs. Leaves pinnately 3-foliolate; stipules adnate to petiole at base; leaflets denticulate, lateral veins running out into teeth. Racemes axillary, flowers crowded into heads; bracts small and caducous. Calyx 5-toothed, subequal. Petals free from staminal tube; standard oblong to obovate, usually reflexed; wings and keel with hooked appendages involved in explosive tripping mechanism for pollination. Stamens diadelphous; filaments not dilated, apical portion of staminal column arched; anthers uniform. Ovary sessile or shortly stipitate; ovules numerous; style subulate; stigma subcapitate, oblique. Legume compressed, coiled, curved, or straight, surface reticulate, sometimes armed with spines. Seed small, reniform, smooth or rough.
About 85 species: Africa, C and SW Asia, Europe, Mediterranean region; 15 species (one endemic, six introduced) in China.