Survival and genetic divergence of an arctic-alpine plant, Diapensia lapponica subsp. obovata (Fr. Schm.) Hultén (Diapensiaceae), in the high mountains of central Japan during climatic oscillations

Previous phylogeographic studies of arctic-alpine plants have partly elucidated that alpine areas at the southernmost edges of their distribution have been one of the most important areas for the survival of populations through Quaternary climatic oscillations. To reveal the genetic structure of arctic-alpine plants near the southern edge of their range in East Asia, 159 samples of Diapensia lapponica subsp. obovata (Diapensiaceae) were collected from 22 populations in Japan. Based on 1,134 bp of chloroplast DNA (cpDNA), we determined 10 haplotypes. Neighbor-joining (NJ) analysis, including D. lapponica from Sweden and Schizocodon soldanelloides, revealed that all haplotypes in Japan were monophyletic. Genetic differentiation between populations of central Honshu and northern Japan was strongly supported by the NJ tree (100%), analysis of molecular variance (AMOVA, 68%), and Monmonier’s algorithm (>95%). The most ancestral haplotype rarely occurred in Japan, which implied that the extant genetic structure was not caused by genetic divergence during colonization. Thus, these results suggest that the arctic-alpine plant D. lapponica subsp. obovata survived climatic oscillations in central Honshu. This finding supports the hypothesis that high mountains in temperate regions were important for survival of arctic-alpine plants during Quaternary climatic oscillations.