Molecular phylogeny, divergence time estimates, and historical biogeography of Circaea (Onagraceae) in the Northern Hemisphere

Circaea (Onagraceae) consists of eight species and six subspecies distributed in Eurasia and North America. The sister group of Circaea was recently shown to be Fuchsia, which comprises 107 species primarily distributed in montane Central and South America, including four species occurring in the South Pacific islands. Three plastid markers (petB–petD, rpl16, and trnL-F) and nrITS sequences from 13 of the 14 taxa of Circaea were sequenced and used to reconstruct the phylogenetic and biogeographic history of the genus. Parsimony and Bayesian analyses support that (1) Circaea is monophyletic; (2) the bilocular group is a weakly supported clade nested within the unilocular grade; (3) neither the C. alpina complex nor the C. canadensis complex is monophyletic; and (4) the western North American C. alpina subsp. pacifica diverged first in the genus. Divergence time estimates based on the Bayesian “relaxed” clock methods suggest that the earliest Circaea divergence occurred minimally at 16.17 mya (95% HPD: 7.69–24.53 mya). Biogeographic analyses using divergence–vicariance analysis (DIVA) and a likelihood method support the New World origin of Circaea. Three independent dispersal events between Eurasia and North America via the Bering land bridge were inferred within Circaea. Higher taxon diversity of Circaea in eastern Asia was probably caused by geologic and ecological changes during the late Tertiary in the Northern Hemisphere.