@article{xiang_thorne_seo_zhang_thomas_ricklefs_2008, title={Rates of nucleotide substitution in Cornaceae (Cornales)—Pattern of variation and underlying causal factors}, volume={49}, ISSN={10557903}, url={https://linkinghub.elsevier.com/retrieve/pii/S1055790308003606}, DOI={10.1016/j.ympev.2008.07.010}, abstractNote={Identifying causes of genetic divergence is a central goal in evolutionary biology. Although rates of nucleotide substitution vary among taxa and among genes, the causes of this variation tend to be poorly understood. In the present study, we examined the rate and pattern of molecular evolution for five DNA regions over a phylogeny of Cornus, the single genus of Cornaceae. To identify evolutionary mechanisms underlying the molecular variation, we employed Bayesian methods to estimate divergence times and to infer how absolute rates of synonymous and nonsynonymous substitutions and their ratios change over time. We found that the rates vary among genes, lineages, and through time, and differences in mutation rates, selection type and intensity, and possibly genetic drift all contributed to the variation of substitution rates observed among the major lineages of Cornus. We applied independent contrast analysis to explore whether speciation rates are linked to rates of molecular evolution. The results showed no relationships for individual genes, but suggested a possible localized link between species richness and rate of nonsynonymous nucleotide substitution for the combined cpDNA regions. Furthermore, we detected a positive correlation between rates of molecular evolution and morphological change in Cornus. This was particularly pronounced in the dwarf dogwood lineage, in which genome-wide acceleration in both molecular and morphological evolution has likely occurred.}, number={1}, journal={Molecular Phylogenetics and Evolution}, author={Xiang, Qiu-Yun (Jenny) and Thorne, Jeffrey L. and Seo, Tae-Kun and Zhang, Wenheng and Thomas, David T. and Ricklefs, Robert E.}, year={2008}, month={Oct}, pages={327–342} }
 @article{xiang_thomas_zhang_manchester_murrell_2006, title={Species Level Phylogeny of the Genus Cornus (Cornaceae) Based on Molecular and Morphological Evidence-Implications for Taxonomy and Tertiary Intercontinental Migration}, volume={55}, ISSN={00400262}, url={http://doi.wiley.com/10.2307/25065525}, DOI={10.2307/25065525}, abstractNote={AbstractDNA sequences were generated for matK and ITS for 68 and 103 samples of Cornus to reconstruct a species level phylogeny of the genus. The results support the monophyly of most subgenera, except subg. Kraniopsis and subg. Cornus. Subgenus Kraniopsis was suggested to exclude C. peruviana from South America and subg. Afrocrania and subg. Sinocornus were nested within subg. Cornus. Four major clades corresponding to groups also recognizable by morphological differences were revealed: the big‐bracted dogwoods (BB) including subg. Cynoxylon, subg. Syncarpea, and subg. Discocrania, the dwarf dogwoods (DW) including subg. Arctocrania, the cornelian cherries (CC) including subg. Cornus, subg. Sinocornus, and subg. Afrocrania, and the blue‐ or white‐fruited dogwoods (BW) including subg. Kraniopsis, subg. Mesomora, and subg. Yinquania. This finding is consistent with previous studies with more limited sampling. The single South American species C. peruviana was found to be sister to the Asian C. oblonga of subg. Yinquania, adding a fourth intercontinental disjunction in the genus that was previously unknown. Species relationships within the subgenera were clearly resolved except for the relatively large subg. Syncarpea and subg. Kraniopsis. Phylogenetic analyses of total evidence combining morphology, matK, ITS, and previously published rbcL and 26S rDNA sequences resolved the relationships among subgenera as (BW(CC(BB, DW))). Biogeographic analyses using DIVA with or without fossils resulted in different inferences of biogeographic history of the genus, indicating the importance of fossil data in biogeographic analyses. The phylogeny based on the total evidence tree including fossils supports an origin and early Tertiary diversification of Cornus in Europe and multiple trans‐Atlantic migrations between Europe and North America by the early Tertiary. It also supports that distribution of the few species in the southern hemisphere was not ancestral, but a result of migration from the north. This evidence rejects a previous hypothesis of a southern hemispheric origin of the genus.}, number={1}, journal={Taxon}, author={Xiang, Qiu-Yun (Jenny) and Thomas, David T. and Zhang, Wenheng and Manchester, Steven R. and Murrell, Zack}, year={2006}, month={Feb}, pages={9} }
 @article{xiang_sr_thomas_zhang_fan_2005, title={Phylogeny, biogeography, and molecular dating of cornelian cherries (Cornus, Cornaceae) – tracking Tertiary plant migration}, volume={59}, DOI={10.1554/03-763.1}, abstractNote={Data from four DNA regions (rbcL, matK, 26S rDNA, and ITS) as well as extant and fossil morphology were used to reconstruct the phylogeny and biogeographic history of an intercontinentally disjunct plant group, the cornelian cherries of Cornus (dogwoods). The study tests previous hypotheses on the relative roles of two Tertiary land bridges, the North Atlantic land bridge (NALB) and the Bering land bridge (BLB), in plant migration across continents. Three approaches, the Bayesian, nonparametric rate smoothing (NPRS), and penalized likelihood (PL) methods, were employed to estimate the times of geographic isolations of species. Dispersal and vicariance analysis (DIVA) was performed to infer the sequence and directionality of biogeographic pathways. Results of phylogenetic analyses suggest that among the six living species, C. sessilis from western North America represents the oldest lineage, followed by C. volkensii from Africa. The four Eurasian species form a clade consisting of two sister pairs, C. mas– C. officinalis and C. chinensis–C. eydeana. Results of DIVA and data from fossils and molecular dating indicate that the cornelian cherry subgroup arose in Europe as early as the Paleocene. Fossils confirm that the group was present in North America by the late Paleocene, consistent with the DIVA predictions that, by the end of the Eocene, it had diversified into several species and expanded its distribution to North America via the NALB and to Africa via the last direct connection between Eurasia and Africa prior to the Miocene, or via long-distance dispersal. The cornelian cherries in eastern Asia appear to be derived from two independent dispersal events from Europe. These events are inferred to have occurred during the Oligocene and Miocene. This study supports the hypothesis that the NALB served as an important land bridge connecting the North American and European floras, as well as connecting American and African floras via Europe during the early Tertiary.}, number={8}, journal={Evolution}, author={Xiang, Q.-Y and Sr, Manchester and Thomas, D. and Zhang, WH. and Fan, CZ}, year={2005}, pages={139–155} }
 @article{xiang_zhang_ricklefs_qian_cheng_wen_li_2004, title={Regional differences in speciation and ITS Evolution: A comparison between eastern Asia and eastern North America}, volume={58}, ISSN={["1558-5646"]}, DOI={10.1111/j.0014-3820.2004.tb01596.x}, abstractNote={Abstract The eastern Asian (EAS)‐eastern North American (ENA) floristic disjunction is one of the best‐known biogeographic patterns in the Northern Hemisphere. Recent paleontological and molecular analyses have illuminated the origins of the biogeographic pattern, but subsequent diversification and evolution of the disjunct floras in each of the two continents after isolation remains poorly understood. Although similar in climate and floristic composition, EAS has twice as many species as ENA in genera occurring in both regions. Explaining such differences in species diversity between regions with similar environmental conditions (diversity anomalies) is an important goal of the study of the global patterns of biodiversity. We used a phylogenetic approach to compare rates of net speciation and molecular evolution between the two regions. We first identified EAS‐ENA disjunct sister clades from ten genera (Asarum, Buckleya, Carpinus, Carya, Cornus, Hamamelis, Illicium, Panax, Stewartia, and Styrax) that represent diverse angiosperm lineages using phylogenetic analyses of ITS (internal transcribed spacer of nuclear ribosomal DNA) sequence data. Species richness and substitution rate of ITS between sister clades were compared. The results revealed a pattern of greater species diversity in the EAS counterparts. A positive relationship between species diversity and ITS substitution rate was also documented. These results suggest greater net speciation and accelerated molecular evolution in EAS. The data support the idea that a regional difference in net speciation rate related to topographic heterogeneity contributes to the diversity anomaly between EAS and ENA. The close relationship between rates of ITS evolution and species richness further suggests that species production may be directly linked to rate of nucleotide substitution.}, number={10}, journal={Evolution}, author={Xiang, Q.Y. and Zhang, W.H. and Ricklefs, R.E. and Qian, H. and Cheng, Z.D. and Wen, J. and Li, J.H.}, year={2004}, pages={2175–2184} }