Abstract: Philadelphus (Hydrangeaceae) comprises 60 or fewer species distributed disjunctly in eastern Asia, eastern and western North America to Central America, and southeastern Europe and western Asia. The genus is highly valued in horticulture, but poorly understood regarding taxonomy, species relationships, and biogeographic history. The present study was the first phylogenetic and biogeographic analysis of Philadelphus using both nuclear and chloroplast DNA markers to evaluate classification schemes and to elucidate the biogeographic origin. Our results suggest that Philadelphus is a paraphyletic group with the monotypic genusCarpenteria nested within. Three major lineages were identified in the Philadelphus–Carpenteria clade, each strongly supported by the molecular data. Biogeographic analysis using the Bayes-DIVA method (implemented in the newly developed RASP) and divergence time dating with BEAST resolved the origin and early diversification of Philadelphus s.l. (including Carpenteria) in western North America (including Mexico) in the Eocene. The lineage diversified and subsequently spread into Asia and other areas in the late Tertiary or Neogene to obtain a worldwide distribution. The study adds an additional example of an “out of western North America” migration in the phylogeographic history of the northern hemisphere.

Key words: biogeography, Carpenteria, divergence time, Philadelphus, phylogeny