Four species of European Cardamine have been considered to occur in Japan. Cardamine impatiens L. and C. ftexuosa With, have been treated as pan-Eurasian species that are also native to Japan. Cardamine hirsuta L. and C. parviflora L. have been listed as introduced species. In this study, we compared material from Japan and Europe to evaluate previous treatments. We confirmed the occurrence of C. impatiens and C. hirsuta in Japan, and consider the latter to be an introduced species, as indicated in previous treatments. The Japanese plants identified as C. flexuosa are likely to be different from the original C. flexuosa of Europe. The eastern border of the natural range of the European C. flexuosa is in European Russia, with a wide geographic disjunction between the European and eastern Asian plants. Cardamine flexuosa in central Europe occurs along the edges of montane forests, but the plants in Japan are most common in ricepaddy fields. We found no specimens from Japan of true C. parviflora in the major herbaria of Japan. Further rigorous systematic and nomenclatural studies are required to determine the status of the plants that have been treated as C. flexuosa in Japan.