Molecular phylogeny and intra- and intercontinental biogeography of Calycanthaceae

Based on nuclear and chloroplast sequences we resolve species relationships in Calycanthaceae and develop a biogeographic hypothesis that explains their intercontinental disjunctions and intra-continental diversification in eastern Asia. Fossil-calibrated penalized likelihood and Bayesian divergence time estimates indicate that the Northern Hemisphere Calycanthus and Chimonanthus diverged from each other in the mid-Miocene, while the Australian Idiospermum had already diverged by the Upper Cretaceous and likely represents a remnant of a former Gondwanan distribution of Calycanthaceae that included South America, as indicated by the occurrence of Cretaceous Calycanthaceae fossils in Brazil. Relationships within Calycanthus were difficult to resolve, but a shared 155-bp deletion in the trnL–F intergenic spacer unites the two North American species, which were also sisters in a cpDNA restriction site study. Their ancestor apparently crossed the Bering land bridge in the Miocene. The six species of Chimonanthus, by contrast, diverged from each other as recently as 1–2 my ago, and a DIVA analysis with four areas of endemism recognized within China suggests three vicariance and two dispersal events within Chimonanthus, with initial vicariance having occurred between eastern and southwestern or central China. Further divergence then appears to have involved eastern and southcentral China, and southwestern and central China.