Abstract
This review compiles information on the morphology, historical taxonomic treatments, species origin, gene pool concept, geographical and ecological habitats, and stress tolerance of the azuki bean (Vigna angularis) and related species. Willdenow (1802) first described the azuki bean in the genus Dolichos, and Ohwi and Ohashi (1969) finally transferred it to the genus Vigna. The genus Vigna is currently divided into five subgenera: Ceratotropis, Haydonia, Lasiospron, Plectrotropis, and Vigna. The subgenus Ceratotropis includes the moth bean in section Aconitifoliae; the mungbean and black gram in section Ceratotropis; and the azuki bean, rice bean, and creole bean in section Angulares. The wild species in section Angulares generally possess larger standard petal with more prominent appendage, keel petal with longer pocket, pistil with longer style beak compared with those of species in sections Aconitifoliae and Ceratotropis, and characterized by glabrous mature pod, smooth seed coat, hypogeal germination seed, and cordate primary leaves with petiole. Section Angulares currently consists of 13 species. The taxa that cross readily with the azuki beans included in the primary genepool are the wild azuki bean V. angularis var. nipponensis, V. nepalensis, V. tenuicaulis, V. hirtella, V. minima, V. nakashimae, and V. riukiuensis. These wild species are expected to be used as breeding material against biotic and abiotic stresses.