<国立科博専報>奄美大島におけるホシダとケホシダおよびその自然雑種の形態変異
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Thirteen populations of Cyclosorus acuminatus, C.parasiticus and their putative hybrid from Amami Island which lies on 29°00' -29°30' N.latitude, 129°00' -129°50' E.longitude have been investigated for morphological variations within a single individual (phenotypic plasticity), between individuals (individual variation) and between populations (population variation). The aim was to carify the above variation and the region of the species. The locality of each population is given in Table 1 and Figure 1. The following characteristics were observed : the shape and size of the spores, chromosome numbers, hair on the surface of leaf and the shape of indusium. Measured parts are indicated on Figure 2. To investigate phenotypic plasticity and individual variation, all leaves were taken from a single individual within each population. To study variation between populations, the largest fertile leaf was taken from all individuals in each population. The samples collected consisted of 133 specimens from 13 populations. These specimens were divided into two types based on the shape and size of the spores. As a result, 59 specimens had regualr spores and 74 specimens had irregular spores. The 59 specimens which had regular spores were determined to be C.acuminatus, (25 specimens) and C.parasiticus, (34 specimens) by Nakaike's system (Nakaike 1982). Other specimens which had irregular spores were determined to be a putative hybrid between C.acuminatus and C.parasiticus. Chromosome counts indicated that C.acuminatus was 2X(2n=74), C.parasiticus was 4X(2n=144), and putative hybrid was 3X(2n=108), The results of chromosome counts supported the claim that a putative hybrid is a hybrid between C.acuminatus and C.parasiticus. Phenotypic plasticity in a single individual showed variation in the size of the leaf (FL, SL, PL, PW, AN, LL). However, in the number of midrib branches (NV) and number of costa branches (PNV), there was almost no variation. In terms of individual variation, variations in the number of midrib branches (NV) and costa branches (PNV), and sours (SN) were observed. In the variation between populations variation in pinna width (PW) was observed. The morphological characteristics (shape and size of spore, chromosome number, hair on surface of leaf, shape of indusium, number of midrib branches of apex of lamina and number of costa branches) were independent between C.acuminatus and C.parasiticus. The putative hybrid combines the morphological features of C.acuminatus and C.parasiticus which are its putative parents. The morphological variations between the putative hybrid and C.parasiticus overlap with regard to variations of spore ornamentation, hair on surface of leaf and shape of leaf, so the species are not distinguished by the above characteristics. However, the three species are obviously distinguished by the number of joined lateral veins (AN), the distance between two adjacent stipe of rhizome (SD) and stomata length (STL). The distance between two adjacent stIpe of rhizome (SD) is an especially useful diangostic characteristic to discriminate between the three specles.
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