Description from Flora of China
Herbs annual, 15-100 cm tall. Stem unbranched to much branched, decumbent or climbing, puberulent or pilose. Leaves paripinnate, 2-10 cm; stipules hastate, semisagittate, or lanceolate, ca. 1.5 mm, 2-5-toothed, puberulent; leaflets 2-7-paired, linear to oblong-cuneate to obcordate, 9-25 × 2-10 mm, hairy, apex acute, obtuse, truncate, or emarginate, mucronate; lateral veins not obvious; tendril 2- or 3-branched. Flowers 1 or 2(-4) in axillary fascicles. Calyx campanulate, hairy; teeth shorter than to longer than tube. Corolla blue-purple or purple to red, (8-)10-30 mm; standard long obovate or obovate, constricted at middle, subequaling or longer than wings; wings longer than keel. Ovary shortly stalked, linear or fusiform, puberulent or hairy; ovules 5-8. Legume black, brownish black, brown, or yellow-brown, linear or linear-oblong, slightly curved, contracted or not contracted between seeds, 25-70 × (2.5-)3-11 mm, pubescent to glabrous, apex beaked. Seeds 4-8, spheroid. Fl. Jan-Aug, fr. Feb-Sep. 2n = 10, 12, 14.
Wild or cultivated and possibly naturalized, forests, hedges, hill slopes, valleys, grasslands, dry pastures, damp grassy places, river and creek banks, river beds, farms, orchards, fields, cultivated land, margins of cultivation, wastelands, roadsides; sea level to 3700 m. Anhui, Chongqing, Fujian, Gansu, Guangdong, Guizhou, Hebei, Heilongjiang, Hubei, Hunan, Jiangsu, Nei Mongol, Sichuan, Taiwan, Xinjiang, Xizang, Yunnan, Zhejiang [Afghanistan, Bhutan, India, Japan, Kazakhstan, Korea, Kyrgyzstan, Mongolia, Nepal, Pakistan, Russia, Tajikistan, Turkmenistan, Uzbekistan; Africa, SW Asia, N Atlantic islands, Europe; widely introduced and naturalized elsewhere].