The area of the present study includes Hokkaido, Saghalien, the Kuriles, the Commander Islands and the Aleutian Islands. The species of Polypodiales growing in the area under consideration attain 99 in total number, the genera 46 and the families 5. Endemic species : Except only one species, namely Polystichum aleuticum which occurs very locally in the middle part of the Aleuian Islands, there is no endemic species. Only two species, namely Polystichum microchlamys and Ctenitis quelpaertensis have their distribution center in the area above mentioned. Disjunctive distribution : Polystichum Lonchitis offers a typical example of disjunctive distribution. The northern limits of the plant distribution are sometimes found in disjunctive lolcalities : for examples of the fern, there are Asplenium incisum in Kamtchatka, Cyrtomium Fortunei, Dryopteris Dickinsii, Lepisorus Onoei in the Island of Okushiri of Hokkaido, Dryopteris laeta in the eastern part of Hokkaido, Dryopteris monticola and Pentarhizidium japonicum in the Island of Kaiba of S. Saghalien. Common species : The common and wide ranging species are Athyrium melanolepis, Dryopteris austriaca and Phegopteris polypodioides. They are all circumpolar elements. Warm temperate elements : As the warm temperate elments, there are Cyrtomium falcatum, Cyrtomium Fortunei, Davallia Mariesii, Dryopteris Dickinsii, Dryopteris lacera, Dryopteris Sabaei, Lepisorus Onoei, Neoniphopsis linearifolia, etc. They occur only in the southwestern part of Hokkaido. Temperate elments : The temperate elements are found in the districts of the southern part from the SCHMIDT'S Line in Saghalien and also of the southern part from the MIYABE'S Line in the Kuriles including Hokkaido. For the area including northern Korea, eartern Manchuria, southern Kuriles and also Hokkaido excluding the south-western part, from the phytogeographical point of view, the writer proposed to delimit an intermediate zone between the temperate Eastern Asia and the Siberian subarctic zone. Subarctic elements : As subarctic elements, there are Athyrium crenatum, Dryopteris austriaca, Gymnocarpium Dryopteris, etc. In spite of the lack of the needle forest, it is very interesting that the common ferns of subarctic elements occur in the northern islands of the present study. In conclusion, the most remarkable character of the region is the sudden decrease of the floral influence of Polypodiaceae of the temperate Estern Asia at MIYABE'S Line and SCHMIDT'S Line.
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