Abstract
Haplopteris mediosora (Hayata) X. C. Zhang (Pteridaceae), a fern with linear simple fronds is widely distributed at high elevations from the Himalayas through China, the Philippines and Taiwan to Japan. In Japan, sporophytes of H. mediosora were recorded only from Azusa-shiraiwa, a mountain of Okuchichibu region, and have not been seen for over 50 years. The hypothesis that such rare species still persist as gametophytes was proven during this study when gametophytes were found on several mountains in the Oku-chichibu region. Phylogenetic analysis of rbcL sequences collected in this study demonstrated that the gametophytes, identified as H. mediosora, and sporophytes of H. mediosora formed a clade and were distinct from related species of Haplopteris. The gametophytes were also growing independently because of the absence of sporophytes. A comparison of the haplotypes of the matK and trnL-F regions showed that the gametophytes had two chloroplast DNA haplotypes. The polymorphisms may have been derived from ancestral sporophytes that were present in Japan during the glacial period. Despite the rarity of sporophytes in the area, the independent gametophytes occur in four distant localities in the Oku-chichibu mountains.
