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Three different interpretations have been put forward for the taxonomic treatment of the reedgrass growing on high altitudes of Isl. Yakushima, Kagoshima Prefecture : (1) the entirety of the population should be treated as an independent species, Calamagrostis masamunei HONDA (OHWI, 1936, 1975) ; (2) it may be a local variant of C. longiseta HACK. whose main range is situated in Honshu (KOYAMA, 1964) ; (3) the population in question would include two species, C. masamunei and C. longiseta (HONDA, 1930). For convenience, "C. masamunei" is hereafter used in the sense that it covers the entirety of the population in question. With the aim of getting a better taxonomic understanding of the plants concerned, I have attempted to clarify the variability in morphological features, chromosome number and habitat preference of C. masamunei, and to confirm whether C. masamunei has some traits clearly distinct from C. longiseta distributed in Honshu. My field explorations have confirmed that C. masamunei is not greatly variable in ecological preference .Chromosome counts for 82 individuals have revealed that C. masamunei is principally tetraploid with 2n=28 though a few individuals have shown one to four B chromosomes besides the ordinary A chromosomes (see Appendix 1). So far as known, plants of Calamagrostis having 2n=28 are self-incompatible and outcrossing (NYGREN, 1946, 1962), and the same may be true of C. masamunei. C. masamunei varies rather greatly in culm height (10-60 cm), but this variation does not suggest the presence of two taxa since the extremes are connected by numerous plants with intermediate culm height (cf. Fig. 1). The examination of various spikelet features of 71 collections of C. masamunei has indicated that it is not unusually variable in these characters (Table 1), and that the extents of the variability found in C. masamunei are similar to or smaller than those found in tetraploid populations of four species of Calamagrostis distributed in Central Honshu (Table 2). These results clearly show that the plants on Isl. Yakushima have a unity as one and the same taxon. Thus, the interpretation (3) designated above should be rejected. The collections of C. masamunei have been compared morphologically with individual specimens of C. longiseta preserved in herbaria. It has become clear that these two groups of plants more or less deviate in several characters. The most obvious difference has been detected in a combination of the two characters appearing in Fig. 2; ratio of callus hair length and lemma length, and relative position of awn insertion on the back of lemma. In order to confirm to what extents local populations of C. longiseta in Honshu vary in these characters, 20 individuals from each of the five selected populations have been examined. The results are shown in Fig. 3. It is evident that the local populations of C. longiseta are considerably variable and largely overlap in the range of variation in these characters, while they are disparate from C. masamunei. Thus, the results obtained are in favor of the interpretation (1) and are disharmonious with the interpretation (2). The conclusion has been drawn that C. masamunei exists as an independent species which has most probably been brought about through the process of geographical speciation as part of the evolutionary differentiation at the 2n=28 level.
日本植物分類学会の論文
1982-04-20

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