Japan Flora: Closely related to O. corniculata; rhizomes elongate, very slender, loosely and minutely scaly; stems 20-40 cm. long, usually simple; leaves long-petioled; stipules indistinct; inflorescence cymose; flowers 1 or 2, rarely 3, pedicellate, the bracts small; seeds rather large, 1.5-2 mm. across. July-Oct. Thickets and thin woods.
Hokkaido, Honshu (centr. distr. and northw.). Temperate Asia and N. America, introduced in Europe.