Description from Flora of China
Hedysarum tortuosum Swartz, Prodr. 107. 1788; Desmodium purpureum (Miller) Fawcett & Rendle; H. purpureum Miller.
Herbs, perennial, erect, 50-200 cm tall. Stems with hooked hairs, sometimes intermixed with long hairs. Leaves 3-foliolate, rarely 1-foliolate; petiole 1-8 cm, hairy as stems; terminal leaflet blade elliptic or ovate, 3-8(-14) × 1.5-3(-6) cm, both surfaces sparsely hairy, base cuneate, apex obtuse. Racemes or sometimes panicles, terminal or axillary; rachis with dense minute hooked and glandular hairs, 2-flowered at each node. Pedicel filiform, to 1.7 cm at fruiting, hairy as rachis. Calyx 3-4 mm, 5-parted; lobes longer than tube. Corolla red, white, or yellow; standard obovate, 2.5-3.5 × ca. 2 mm, base attenuate, apex emarginate; wings oblong, base auriculate, shortly clawed; keel obliquely oblong, clawed. Legume narrowly oblong, 1.5-2 cm, both sutures constricted between articles, moniliform, densely gray-yellow hooked hairy, (3-)5-7-jointed. Fl. and fr. Jul-Sep. 2n = 22.
Wastelands, plains; low elevations. Introduced and naturalized in Guangdong [native from S United States to subtropical South America; naturalized in tropics of Old World].