Abstract
We report for the first time a diploid cytotype (2n-54) in the Thelypteris angustifrons complex from Okinawa Isl., the Ryukyus, although a hexaploid (2n 162, x=27) or a hyperhexaploid (2n-164) has been reported from Japan (Kyushu and Honshu) and a diploid (n=31) from Taiwan. The hexaploid is also found in Amami-oshima Isl. and more northern Japan. In addition, a triploid (2n=81) and a hypotetraploid (2n-107) are found in Amami-oshima Isl. and may be hybrids, because of irregular spore morphology. The spores of the diploids have less developed perispore and are smaller than those of the hexaploids. A variation in spore size of herbarium specimens examined shows that putative diploids occur only on Okinawa and Yakabi Isls. The diploid cytotype seems to be restricted to Okinawa and its neighboring area and also probably to Taiwan, while the hexaploid seems to be widely distributed from Taiwan north to warm temperate regions of Japan. From differences in chromosome number and spore and leaf morphologies, the diploid cytotype is regarded as T. miyagii, a species independent of the hexaploid T. angustifrons. The two related species, T. glanduligera and T. cystopteroides, were compared to the complex.
