南硫黄島の維管束植物相(<特集>南硫黄2007)

2007年6月の南硫黄島調査において採集された約700点の維管束植物標本を固定した結果、現時点までに96種(未同定種も含む)が確認された。南硫黄島において初めて確認された植物は、ミズスギ、オオハナワラビ属の1種、コケシノブ科の1種、ホングウシダ、ナチシケシダ、シンクリノイガ、イネ科の1種、テンツキ属の1種、コクランの9種であった。過去に発表された植物リスト(大場、1983)と、今回の調査によって確認された種を合わせると、本島には、シダ植物44種、双子葉植物59種、単子葉植物26種、合計129種が記録された。これらの中には18種の絶滅危惧種(準絶滅危惧も含む)とともに数種の外来植物も含まれ、特に25年前には全く確認されなかったシンクリノイガが島内に広く生育していることが確認された。これらの外来植物は鳥や風・海流などを介して運ばれた可能性が高いことから、今後も周辺の島から新たな植物が侵入することが懸念される。

Minami-Iwo-To Island is small volcanic island located 1300 km south of Tokyo. The flora of this remote island had been studied infrequently because of the difficulty of access. Since the island's discovery, only three major botanical expeditioas had been accomplished in 1935,1936 and 1982. In order to assess the current floristic diversity of the island, a botanical expedition was carried out during 17-27 June 2007 and about 700 specimens were collected. In this expedition, ninety-six vasucular plant species were identified of which nine species as new to the island: Lycopodium cernuum L., Botrychium sp., Hymenophyllaceae sp., Lindsaea odorata Roxb., Deparia petersenii (Kuntze) M.Kato, Cenchrus echinatus L., Gramineae sp., Fimbristylis sp. and Liparis nervosa (Thunb.) Lindl. One hundred and twenty-nine plant taxa occurred in this island as a result from compiling the previous and this studies. Twenty-three threatened species, including near threatened ones, were recorded there, eighteen species of them were found in this study. Cenchrus echinatus L. is known as invasive alien species in the Bonin Island and was not found in previous expedition of 1982. This species is considered dispersed by bird or ocean current from the other island of the Bonin Islands. Therefore, inspection and monitoring should be implemented in order to minimize the accidental introduction of exotics to this island.