The Hengduan Mountains region of south-west China is a noted biodiversity hotspot,but the geographic origins and historical assembly of its rich endemic flora,including the sky-island species of Solms-laubachia Muschl.(Brassicaceae),have been little studied.Previous molecular studies on the phylogeny of Solms-laubachia showed it to be paraphyletic,leading to considerable expansion not only of its taxonomic limits,but also its geographic range,with the inclusion of taxa from outside the Hengduan region.However,these studies provided little resolution of interspecific relationships,preventing inferences about historical biogeography within the clade.In the present study,new sequence data from two nuclear genes(LEAFY and G3pdh) and two chloroplast intergenic spacers(petN-psbM and psbM-trnD) were combined with existing markers to increase phylogenetic signals.Phaeonychium villosum(Maxim.) Al-Shehbaz was found to be nested within Solms-laubachia s.l.In general,phylogenetic relationships appear to be a good predictor of geography,with the Hengduan Mountain endemics embedded in a paraphyletic grade of species from the western Himalayas and central Asia,but they also imply morphological homoplasy.Incongruence was detected between the nuclear and chloroplast gene trees,perhaps resulting from incomplete lineage sorting of ancestral polymorphisms.The crown age of Solms-laubachia s.l.was estimated to be approximately 1.42-3.68 mya,using Bayesian relaxed molecular clock analysis.Historical biogeographic analysis using a parametric dispersal-extinction-cladogenesis model inferred central Asia and the western Himalayas as most probable ancestral range of Solms-laubachia s.l.,and estimated higher rates of eastward expansion than westward during the diversification of descendant lineages.In summary,our results suggest that Solms-laubachia s.l.originated during the Pliocene in central Asia,and subsequently migrated eastward into the Hengduan Mountains,colonizing sky-island,alpine scree-slope habitats that may have provided novel e
Ji-Pei YUEHang SUNDavid A. BAUMjian-Hua LIIhsan A. AL-SHEHBAZRichard REE
Toxicodendron is a genus in the Rhus complex of Anacardiaceae with a disjunct distribution between eastern Asia and North America,extending to southeastern Asia and the neotropics.Nuclear(internal transcribed spacer,external transcribed spacer,and NIA-i3) and chloroplast(ndhF and trnL-F) sequences were used to construct phylogenetic relationships of Toxicodendron.Phylogenetic analysis of these data strongly support Toxicodendron as a monophyletic group distinct from other genera of the Rhus complex,and the phylogeny does not fully corroborate classification at the sectional level.Two temperate disjunct lineages were detected,one from section Toxicodendron and the other between the eastern North American Toxicodendron vernix and the eastern Asian Toxicodendron ver-nicifluum.Their divergence times were estimated to be 13.46(7.95-19.42) and 7.53(2.76-12.86) mya,respectively.The disjunction between section Griffithii(taxa from warm temperate to tropical Asia) and Toxicodendron striatum(from the neotropics) was supported and their divergence time was estimated to be 20.84(11.16-30.52) mya in the early Miocene.Our biogeographic results and the paleontological data support the Bering land bridge as the most likely route to explain the temperate disjunctions,yet the tropical disjunction in Toxicodendron seems to be best explained by the North Atlantic land bridge hypothesis.
