Phylogenetic analysis of Toxicodendron(Anacardiaceae) and its biogeographic implications on the evolution of north temperate and tropical intercontinental disjunctions

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 Toxieodendron 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 vernieifluum. 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 Toxieodendron striatum （from the neotropics） was supported and their divergence time was estimated to be 20.84 （11.1 6-30.52） 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.

Cytological study on the genus Syncalathium (Asteraceae-Lactuceae),an endemic taxon to alpine scree of the Sino-Himalayas

Cytological characters of four species in Syncalathium （Asteraceae： Lactuceae）, a small genus with six identified species endemic to alpine scree of the Sino-Himalayan region, are surveyed in this report. Three species （Syncalathiumpilosum, Syncalathium chrysocephalum, and Syncalathium disciforme） are examined for the first time. Combined with our previous counts, five species have been cytologically investigated from the genus and the results indicated that all species are diploid with the basic somatic chromosome number of x=8. The karyotype asymmetry of Syncalathium souliei is 2A, distinct from the other four species of 1A, and the remaining species are divided into two subgroups with different karyotypes, consistent with their morphological features. The significance of the cytological evolution of Syncalathium is briefly discussed.

Phylogeny and biogeography of Maianthemum(Asparagaceae:Nolinoideae)revisited with emphasis on its divergence pattern in SW China

Maianthemum is a genus with more than 35 species from the tribe Polygonateae(Asparagaceae),widely distributed between North to Central Americas and eastern Asia with high diversity in the easternHimalayas to the Hengduan Mountains of SW China.Although most species from SW China form a well-supported clade,phylogenetic relationships within this clade remain unclear.With a broad level of taxon sampling and an extensive character sampling fromeight DNA regions,this study intends to revisit the phylogeny and biogeography of the genus to better understand the divergence patterns of species from SW China.Phylogenetic results suggested the monophyly of Maianthemum with recognition of nine strongly supported clades,but backbone relationships among these clades remained largely uncertain.For the SWChina clade,individuals from the same species are grouped into different lineages.Our results revealed that the fast radiation of the SWChina cladewas occurred in the eastern Himalayas,followed by subsequent radiation in the Hengduan Mountains in the Pliocene.Intercontinental disjunctions of Maianthemum in the Northern Hemisphere appear to have occurred multiple times during the late Miocene to the Pliocene,likely resulted by a combination of both vicariance and long-distance dispersal events.

Climate-influenced boreotropical survival and rampant introgressions explain the thriving of New World grapes in the north temperate zone

The north temperate region was characterized by a warm climate and a rich thermophilic flora before the Eocene,but early diversifications of the temperate biome under global climate change and biome shift remain uncertain.Moreover,it is becoming clear that hybridization/introgression is an important driving force of speciation in plant diversity.Here,we applied analyses from biogeography and phylogenetic networks to account for both introgression and incomplete lineage sorting based on genomic data from the New World Vitis,a charismatic component of the temperate North American flora with known and suspected gene flow among species.Biogeographic inference and fossil evidence suggest that the grapes were widely distributed from North America to Europe during the Paleocene to the Eocene,followed by widespread extinction and survival of relicts in the tropical New World.During the climate warming in the early Miocene,a Vitis ancestor migrated northward from the refugia with subsequent diversification in the North American region.We found strong evidence for widespread incongruence and reticulate evolution among nuclear genes within both recent and ancient lineages of the New World Vitis.Furthermore,the organellar genomes showed strong conflicts with the inferred species tree from the nuclear genomes.Our phylogenomic analyses provided an important assessment of the wide occurrence of reticulate introgression in the New World Vitis,which potentially represents one of the most important mechanisms for the diversification of Vitis species in temperate North America and even the entire temperate Northern Hemisphere.The scenario we report here may be a common model of temperate diversification of flowering plants adapted to the global climate cooling and fluctuation in the Neogene.