1. Medicago lupulina Linnaeus, Sp. Pl. 2: 779. 1753.
天蓝苜蓿 tian lan mu xu
Annual or short-lived perennial herbs, 15-60 cm, glabrescent to pubescent, sometimes glandular. Stems decumbent, prostrate or ascending, much branched. Stipules ovate-lanceolate, to 10 mm, entire or toothed, base rounded or hastate, apex acuminate; petiole 1-2 cm; leaflets elliptic, ovate, or obovate, 5-20 × 4-6 mm, papery, pubescent, lateral veins to 10 pairs, base cuneate, margin distally obscurely serrate, apex truncate or retuse, apiculate. Flowers 10-20 in small heads; peduncles slender, straight, longer than subtending leaves, glabrate to densely appressed pubescent; bracts bristlelike, minute; pedicel less than 1 mm. Calyx ca. 2 mm, glabrate to densely hairy. Corolla yellow, 2-2.2 mm; standard suborbicular, apex retuse, longer than wings and keel. Ovary broadly ovate; ovule 1. Legume reniform, ca. 3 × 2 mm, sculptured with concentric arcuate veins, sparsely hairy, black when ripe. Seed 1, brown, ovoid, smooth. Fl. Apr-Sep, fr. Jun-Oct.
Stream banks, roadsides, waste fields, woodland margins. Throughout China [Asia, Europe].