The Lentil vetch (Vicia tetrasperma) belongs to Fabaceae (the Pea family). It is a biennial herb that is distributed from Honshu to Shikoku, Kyushu in Japan, as well as Taiwan, China, and widely temperate regions of Eurasia. It grows in fields and along roadsides, and twines around itself with its tendrils. The leaves are pari-pinnate compound with 3 to 6 pairs of leaflets. 1 to 3 small, pale blue-purple, papillionaceous flowers bloom from the leaf axils with peduncles from April to May. Its Japanese name is derived from its intermediate form between the "Common vetch" (Vicia angustifolia) and the "Hairy tare" (Vicia hirsuta). In Taiwanese Chinese it is called "烏嘴豆" and in Chinese "四籽野豌" (si zi ye wan dou).