トサシモツケの分布と生態

抄録

Spiraea tosaensis YATABE was established based upon the material from the river-course of Shimantogawa in Kochi Prefecture and has been often treated as a variety of Spiraea nipponica MAXIM. So far as our knowledge is concerned, this species is an endemic plant in Shikoku and occurs in the river-courses of Nakagawa in Tokushima Prefecture and Shimantogawa just mentioned. Besides it is rarely found on limestone of Mt. Dairyuji in Tokushima Prefecture (Fig.1). In the river-course of Shimantogawa, the community of this species can usually be found on rocks of the river bank and alluvial soils frequently flooded during the rainy season. The floristic composition and the structure of the community are presented in Table 1. From the phytogeographical point of view it is an interesting fact that many relic and endemic species such as Spiraea tosaensis YATABE, Chrysanthemum yoshinaganthum MAKINO, and others occur on rocky banks in river-courses. The problems on the flora and vegetation in the river-course are briefly discussed in this paper.