Plant Geography of Heterotropa in the Sayama Hills, Western Kanto Plain, with Special Reference to the Quaternary Geohistory
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概要
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The author investigated the geographical distributions of H. nipponica var. nipponica and H. tamaensis in the Sayama Hills, discussing the origin of their distributions in and around the hills with special reference to the geomorphic history in the Quaternary. 1. H. nipponica var. nipponica is widely distributed in the western and central parts of Sayama Hills, while H. tamoaensis narrowly in the southeastern part. But they are not found in the eastern part. 2. For proceeding the discussion, he applied the geomorphic history of the study areas, the facts on their distributions, and their ecological and physiological characters. a) The geomorphic history in these areas shows that the hills (including other hills), uplands, and lowlands have geologically the same beginning but have differentially been dissected because of their different formative ages. Namely, they were formed in the middle Pleistocene, upper Pleistocene, and Holocene, respectively. b) These species are native on the valley side slopes in the Sayama Hills. They are also distributed in other hills which are separated from each other by the younger uplands and lowlands. Moreover, they are sometimes native on the scarps of uplands but never found on the surfaces of uplands and lowlands. c) Depending upon a little seed production, mainly dispersion of seed by ants, and a long term until the progeny grows up, the migration of these species may take much more time than that of weeds or naturalized plants. Their germination and growth require proper wet condition, so that the surfaces of uplands and lowlands look like unsuitable for their establishment because of a super dryness or super wetness on there. They seem to expand their distributions mainly via the scarps of uplands or the valleys of hills, because the scarps and valleys may provide suitable environments for them. 3. He explained that the different distributions of these species in the hills (including other hills), uplands, and lowlands had been controlled both by the internal conditions and the external conditions: the former based on their ecological character of migration and physiological tolerance of life, and the latter on the development of valleys being in proportion to the formative age of each topography. 4. He considered that the distributions of the two Heterotropa species in the Sayama Hills had been relics since the middle Pleistocene on the basis of the above explanation.
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