Sedum tosaense, Makino, 1901

Ito, Takuro, Nakamura, Koh, Park, Chan-Ho, Song, Gwan-Pil, Maeda, Ayako, Tanabe, Yuki & Kokubugata, Goro, 2014, Nuclear and plastid DNA data confirm that Sedum tosaense (Crassulaceae) has a disjunct distribution between Pacific mainland Japan and Jeju Island, Korea, Phytotaxa 177 (4), pp. 221-230 : 227

Dispersal of Sedum tosaense between Japan and Korea

Jeju Island was formed by volcanic activity, which started ~2.0 million years ago (Ma), and by repeated connections and separations to/from the Eurasian Continent ( Woo et al. 2013). Recent biostratigraphic analyses indicate that the Eurasian Continent, including the Korean peninsula and Jeju Island, was connected to the Japanese mainland by a land-bridge that flooded 3.5–1.7 Ma, leading to the formation of the present-day Tsushima Strait ( Kitamura & Kimoto 2006). Our molecular analysis indicated that the populations of S. tosaense in Kochi and on Jeju populations diverged ~0.61 (1.37–0.07) Ma. Therefore, divergence must have occurred much later than the formation of the Tsushima Strait. It is more likely that S. tosaense crossed the water body presently separating the two populations. Some Sedum species have migrated to ocean islands; for example, S. boninense Yamamoto ex Tuyama (1936: 428) occurs on the Bonin Islands, Japan (Tsuyama, 1936) and S. formosanum N.E. Br. (1885: 134) occurs on Lanyu Island, Taiwan ( Tang & Huang, 1993). Presently, no relevant morphological data on the fruits and seeds of S. tosaense suggests a mechanism that would allow the crossing. These data are required to test any putative mechanisms for dispersal across the strait.