Wild and Weed Azuki Beans in Japan

Wild azuki bean, a progenitor of an Asiatic food legume (Vigna angularis var.nipponensis: Fabaceae), and its weed form are distributed widely in the Japanese Archipelago. The straggling or climbing wildform occurs in sleeve or mantle plant communities, and the weakly climbing or bushy weed form is found in relatively open human-disturbed habitats. The wild form has small seeds with a black-mottled pattern on green or grey skin; the weed form has larger seeds with variable color patterns. Wild and weed forms have black, easily dehiscent pods, distinct from their cultivated counterpart which has red large seeds and indehiscent light-colored pods. The wild form is not utilized, but the weed form is recognized by farmers and has several folk names as a weed, a contaminated form of azuki bean, and a substitute for azuki as a food. The frequent occurrence of weed azuki bean in Japan is attributable to adaptation of the wildform to lack of climbing support in human-disturbed habitats, escape from old cultivars, and natural establishment from the derivatives of hybrids between cultivars and wild forms.