Description from Flora of China
Perennial herbs. Rhizome creeping, producing annual erect stems, basal stipules joined to form a sheath, thin and scarious, 3-fid. Leaves digitately 3-foliolate, pedicellate; stipules large, leaflike, free. Racemes leaf-opposed or terminal; bracts connate with lateral stipules, becoming 3(or 6)-fid, persistent; bracteoles absent. Calyx campanulate, or gibbous and baglike on proximal side, 5-toothed. Corolla yellow, rarely purple, petals clawed. Stamens 10, free. Ovules 4-22. Legume linear-oblong or ovate, straight or curved, leathery. Seed reniform or orbicular; hilum small, white.
The genus in China appears to be divisible into three groups. Thermopsis lupinoides and T. chinensis are upright plants with terminal inflorescences, apparently from a single rootstock. Thermopsis lanceolata is an upright plant with terminal inflorescences; there are numerous aerial shoots arising from a spreading rhizome. Thermopsis barbata, T. inflata, T. smithiana, and T. alpina are all precociously flowering species, in which the inflorescences arise early from the rootstock, before the main leafy shoots appear. Then, basal buds on the flowering shoot, below the inflorescence, develop into long leafy shoots completely different in appearance from the precociously flowering material.
About 25 species: C and E Asia and North America; 12 species (four endemic) in China.