ジュウモンジシダの葉形質にみられる地理的クラインと安定性 : 個体発生にともなう脈理と葉形

抄録

Various leaf characters of P. tripteron were measured and compared among different populations in Japan, with reference to geographical topocline of mature plants and heteroblastic leaf development during sporophyte development. Five distributional areas of P. tripteron are recognized in Hokkaido with respect to the frequency (%) of the numbers of collection sites to the research sites in Hokkaido. The five distributional areas seem to correspond to areas represented by the combination between warmth index, difference of monthly mean temperature and number of distinct altitudinal sites. The higher mean NV of fertile leaves (about 80-NV) was found in central and southwestern Hokkaido than that (about 70-NV) in north and eastern Hokkaido, where the lower warmth index (WI<45) was found than other areas. Lower NV at any blade length is found in northern and eastern Hokkaido than the central and south-western Hokkaido during sporophyte development. Lower NV at any BL (above 30-cm stage) was also found in the highland populations than lowland populations on Mt. Teine. This fact supports that the SNV (specific NV, NV/BL, 1/cm) seems to decrease with decreasing WI. SNV corresponds to SNVP (number of costa branches per unit pinna length) and SVL (vein length per unit pinna square, cm/cm^2) (r-0.7 to 0.9). On the other hand, leaf-shape indices such as PL/BL, DI(L/2(3.14×S)^<1/2>) seem to be independent parameters from environmental factors, WI and geographical gradients in Japan. Larger mean NVs of fertile leaves of P. tripteron are found around regions with WI=100 than those of marginal regions with WI<50 or WI>130 in Japan. NV shows high correlations to parameters of DI and PL/BL of fronds (r>0.9) during heteroblastic leaf development. The leaf-shape changes sequentially from ovoidal-wide width to lanceolate-narrow width during heteroblastic leaf development represented by NV. There is a possibility that only leaves with ovoidal-wide width are found around the natural boundary of species distribution. While SNV showed a clear topocline with increasing WI. BL proved to be a correlative character to thermal and geographical gradients among different populations in Japan; however, BL showed high correlation to NV within a distinct population. Leaf-shape indices (NV, DI, PL/BL) seem to be a species-specific character determined sequentially during ontogenetic plant development as if an independent character from the environmental gradient.