Severe climatic oscillations during Quaternary period produced great changes not only in species distribution but also in topography, especially in the Japanese archipelago. During the glacial periods, it was connected to the Eurasian continent by landbridges as a result of the lower sea level. The flora of Japan contains many plant species common to the Eurasian continent, and the species appear to have migrated from the continent into Japan via the landbridges. However, for such species, the migration histories from the continent as well as the differentiation process in the Japanese archipelago were not fully revealed.

In this study, we focused on a diploid clonal herb Cardamine leucantha (Brassicaceae) that widely grows on cool-temperate forest floors and margins in East Asia. We analyzed ten nuclear gene sequences (e.g., F3H, CHS and PHYA) for 96 individuals from 45 populations of Japan, Sakhalin, and Korea, and revealed the migration routes into and differentiation process within the Japanese archipelago.