Non-radiative origin for alpine endemics of Draba (Brassicaceae) in the central mountains of the Japanese Archipelago

Diversity of endemic species may result from two evolutionary processes: in-situ diversification (radiation) or phylogenetically independent divergences (non-radiation). To explore the evolutionary history of endemic-rich alpine flora in the Japanese Archipelago, we investigated the phylogenetic relationships of four endemic taxa of Draba (Brassicaceae) from the high mountains of central Honshu: D. kitadakensis, D. sachalinensis var. shinanomontana, D. sakuraii var. nipponica, and D. shiroumana. Using molecular phylogenetic analyses on plastid trnL-F and nuclear ITS sequence of 157 taxa, we found that the four taxa endemic to central Honshu did not form a monophyletic group and diverged from at least two evolutionary independent lineages. Moreover, ancestral area reconstruction further revealed that some of their ancestral species may have originated from different geographical regions. These findings indicate that the endemic Draba in central Honshu diverged through non-radiative evolutionary origin. Our study suggests that the richness of endemic species in the alpine zone of the Japanese Archipelago is associated with multiple sources with high species diversity located in nearby geographical regions.