Phytogeographical studies ofCalamagrostis sachalinensis (Gramineae)

Abstract

The place of origin and the direction of migration ofCalamagrostis sachalinensis, which has the boreal—montane distribution pattern and represents an apo-amphimictic complex by itself, have been discussed on the basis of the combination of the information on the internal structure of this species and the existing circumstantial evidence. It is without a doubt thatCalamagrostis belongs to a primitive group within the tribe Aveneae, and its existence in Eurasia since the late Miocene period can not be questioned. Amphimictic tetraploids ofC. sachalinensis seem to have originated in the mountains of Japan from some ancestors which invaded Japan in the Neogene period or earlier, considering the distributional and ecological attributes of the tetraploids and the related tetraploid species. The hexaploids and octoploids ofC. sachalinensis with the apomictic manner of seed formation are apparently of a derived type and have most probably been brought forth from the tetrapoid races in the mountains of Japan. The climatic oscillations during the Pleistocene period seem to have greatly facilitated the northward migration of the hexaploids and octoploids. The present range ofC. sachalinensis extending from the mountains of Japan to Sakhalin and southern Kamtchatka may therefore have been established mainly by the migration from the southern montane areas to the northern lowlands. The usual interpretation for the derivation of the boreal—montane distribution which postulates the migration from the north to the south can hardly be applicable in the case ofC. sachalinensis. It is pointed out that the role of autochthonous development in the formation of the montane flora of Japan has probably been more important than hitherto recognized.