Phylogeography of a rare orchid, Vexillabium yakushimense: comparison of populations in central Honshu and the Nansei Island chain, Japan.

Vexillabium yakushimense is a rare, terrestrial orchid which occurs in east and southeast Asia. In spite of its inconspicuous appearance, several new populations were discovered in central Honshu, Japan. Because these populations are geographically isolated at its northern range limit of distribution, they were suspected to have distinctive genetic characteristics. Given this hypothesis, we quantified the genetic variation of V. yakushimense for populations of central Honshu, and the Nansei Island chain, which represent the most southern locality in Japan. Leaves were collected from nine populations in central Honshu ( n = 48) and two populations from the Nansei Island chain ( n = 29). We examined genetic variation using cpDNA (1,205 bp) and ITS (511 bp) markers. Based on the cpDNA variation, a total of seven haplotypes were recovered; populations in central Honshu were clearly differentiated from those in the Nansei Island chain. Relatively high allelic richness and haplotype diversity were found in the pooled population of central Honshu. These populations likely maintained an adequate population size for a long period despite a markedly different ecological niche compared to that in the Nansei Island chain. In contrast to cpDNA, little variation was detected in ITS. Further studies on geographic occurrences, reproductive biology and mycorrhizal association are encouraged for its conservation. [ABSTRACT FROM AUTHOR]