"Ira-kusa" (Urtica thunbergiana) belongs to Urticaceae (the Nettle family). It is a perennial herb that is distributed westward from Kanto district of Honshu to Shikoku, Kyushu of Japan, as well as the Korean Peninsula. This herb grows in montane forests or forest edges, and can reach 40-100 cm in height. The stem is quadrangular and bears needle-like stinging hairs sparsely. The leaves are ovate, opposite with large toothed edges and cuneatic tips. They have scattering short hairs and stinging hairs on the surfaces. The female clusters are borne on the upper stems and the male clusters at the middle stems from September to October. This herb excretes histamine from the stinging hairs, you may feel a burning pain if you touch them accidentally.