A taxonomic study of Asarum sect. Asiasarum (Aristolochiaceae) in Japan

Three species and one variety of Asarum sect. Asiasarum have hitherto been known in Japan. They are reclassified into seven species including three new species: A. maruyamae, A. tohokuense, and A. mikuniense. Most of the taxonomic studies on the section gave weight to the characters of leaves, calyx lobes, and the number of stamens and pistils. However, this study is base on the following characters to distinguish the species: color pattern in the adaxial surface of calyx tube, the shape of calyx tubes, the width of calyx tube throat, the shape of calyx lobe, and the number and height of ridges on inner surface of calyx tubes. The distribution range of the seven species are geographically segregated. Asarum sieboldii is distributed in central and western Honshu, as well as Korea and central to southern China; A. misandrum in Kyushu, the Aso Mountains as well as southern Korea; A. heterotropoides var. heterotropoides in northern Honshu, Hokkaido, southern Sakhalin and Kuriles; A. tohokuense in central and northern Honshu; A. mikuniense in central Honshu; A. maruyamae in western Honshu; A. dimidiatum in western Honshu, Shikoku and Kyushu.