"Katen-so" (Nanocnide japonica) belongs to the Urticaceae (the Nettle family). It is a perennial herb that is distributed from Honsho to Shikoku, Kyushu of Japan, and also Taiwan, the Korean Peninsula and central China. This herb grows in hill to mountain forests and grasslands, and can reach 10-30 cm in height. It grows in clumps by stolons. The stems are often tinged dark purple. The leaves are diamond-ovate, obtuse serrated and arranged in alternate. It is monoecious and the inconspicuous flowers blooms from April to May. The male clusters are borne at the upper axils with long peduncles. The sessile, female clusters are borne in a cluster at the upper axils.