DISTRIBUTIONAL AND ECOLOGICAL OBSERVATIONS OF HISTIOPTERIS INCISA J. SMITH IN IZU PENINSULA

Abstract

In Izu Peninsula, Histiopteris incisa J. SMITH is found on the western coast particularly both in the Shinden and Yagisawa districts of Toicho, Jinden, Kamo-mura, Kamo-gun, and also in the Kumomi district of Matsuzakicho (Fig. 1). As a result of our research, it has been proved that the Shinden district is the northernmost habitat of this fern in Japan as well as in Izu Peninsula. The mentioned four districts taken together occupy an area of about 1000m^2 ; such a large area of habitat is rarely found in Honshu. In Izu Peninsula, the habitats of this species are near streams, in swamps, by ditches, and in places influenced by springs or dripping water from cliffs. The floristic composition and structure of the community (in this paper, those of Yagisawa habitat are chosen) are presented in Table 1. It is a noticeable fact that so far as the distribution of the fern genera are concerned, these habitats are found on and near the line of annual mean temperature of 15.5℃, which corresponds to the mean temperature of 6℃ in these districts in winter (December, January and February).