Phylogenetic patterns and disjunct distribution in Ligularia hodgsonii Hook. (Asteraceae)

Aim The objectives of this study were to elucidate the phylogenetic origins and phylogeographical history of Ligularia hodgsonii, which exhibits a disjunct distribution between south-western-central China and Japan. Location China and Japan. Methods Three chloroplast DNA (cpDNA) spacer regions (trnQ-5' rps16, trnL-rpl32 and psbA-trnH) were sequenced in 280 individuals of L. hodgsonii isolated from 29 natural populations, including 23 from China and 6 from Japan. Phylogenetic inference was performed using MrBayes and beast analyses. Statistical dispersal-vicariance analysis (S-DIVA) was utilized to resolve the biogeographical events in L. hodgsonii, and to clarify the origin of the species' disjunct distribution. Results Genetic variation in cpDNA revealed 19 unique haplotypes among populations. A high degree of genetic diversity (HT = 0.913) and a significant level of differentiation (GST = 0.933, NST = 0.989) were detected. Different haplotypes from continental and island populations were analysed, and the degree of genetic diversity observed within each of the two regions was similar. S-DIVA analysis supported the occurrence of a vicariance event between the continental and island areas. Main conclusions Based on S-DIVA analysis, the non-overlapping cpDNA haplotypes and similar genetic diversity levels in continental and island populations, we conclude that the disjunct distribution of L. hodgsonii is the result of vicariance. Molecular dating suggests that the separation between populations on the islands of Japan (northern Honshu and Hokkaido) and mainland Asia occurred during the middle to late Pleistocene. Following divergence, L. hodgsonii populations probably underwent severe range contraction into multiple isolated refugia during the Last Glacial Maximum, when conditions were colder and drier than at present.