Adzuki beans are a species of annual herbaceous plants of the Vigna genus of the Fabaceae family, distributed throughout Southeast Asia and the Himalayas. It has small beans about 5 mm in size. The red variety is best known, but the beans come in black, white, gray, and various variegated shades. The angular cowpea was domesticated in the Himalayas. On the Korean Peninsula and northern China, adzuki were grown as early as 1000 BC. e. Later, cowpea came to Japan, where today it is the second most popular bean after soybeans.