Molecular phylogeny and taxonomic implications of Asarum (Aristolochiaceae) based on ITS and matK sequences

The genus Asarum (Aristolochiaceae) encompasses approximately 120 species from five sections. Taxonomic controversies concerning the genus Asarum and/or its intrageneric classification remain unresolved. In particular, sect. Heterotropa accounts for a large percentage of the genus (80 of 120 species) and is well diverged in the Sino–Japanese Forest subkingdom. Reconstruction of Heterotropa phylogeny and estimation of its divergence times would provide significant insight into the process of species diversity in the Sino–Japanese floristic region. This study encompassed 106 operational taxonomic units (OTUs), and phylogenetic analyses were conducted based on internal transcribed spacer (ITS) and matK sequences. Although the matK sequences provided informative results solely for section Geotaenium, phylogenetic trees based on ITS regions yielded a clear result for several sections. Three sections, Asarum, Geotaenium and Asiasarum, were supported as robust monophyletic groups, whereas Heterotropa had low support. Sect. Hexastylis was revealed to be polyphyletic, suggesting taxonomic reconstruction would be needed. Sect. Heterotropa comprises two clades, which correspond to species distribution ranges: mainland China and the island arc from Taiwan to mainland Japan via the Ryukyu Islands. It is notable that the common ancestry of the latter clade in the eastern Asian islands was highly supported, suggesting that the present species diversity of Heterotropa was initially caused by allopatric range fragmentation in East Asia. We confirmed the phylogenetic relationships of genus Asarum and taxnomic status of sections.