Comparison of genetic and phenotypic variations in disjunct populations of highly polyploid <scp><i>Betula davurica</i></scp> in the Japanese Archipelago with continental populations in a region of northeast Asia

Abstract Betula davurica Pallas is widely distributed in continental regions of northeast Asia but is disjunctly distributed in the Japanese Archipelago. To examine the lower diversity and higher differentiation in genetic and phenotypic variations expected in these disjunct populations compared to the continental populations, genome‐wide single‐nucleotide polymorphism (SNP) genotypes, chloroplast (cp) DNA sequences, and leaf morphology were investigated in seven disjunct populations in Hokkaido and Honshu in comparison to three populations in Primorye, where B. davurica is continuously distributed. SNP genotypes of putative octaploid individuals indicated that genetic diversity was higher in Honshu (0.158 ≤ H E ≤0.176) than in Hokkaido and Primorye (0.145 ≤ H E ≤0.149). Genetic differentiation between Honshu and the other regions (0.011 ≤ F ST ≤0.035) was larger than that between Hokkaido and Primorye (0.002 ≤ F ST ≤0.009) and within regions (0.001 ≤ F ST &lt;0.007). CpDNA ( trn L– trn F) sequences in Honshu were different from those in Hokkaido and Primorye. Variations in leaf shape and size overlapped among populations in the three regions. These results from B. davurica in the Japanese Archipelago are not consistently congruous with the general trends expected in disjunct populations.