Sheng-Xiang Yu

Gymnaconitum, a new genus of Ranunculaceae endemic to the Qinghai-Tibetan Plateau

The monophyly of traditional Aconitum remains unresolved, owing to the controversial systematic position and taxonomic treatment of the monotypic, Qinghai-Tibetan Plateau endemic A. subg. Gymnaconitum. In this study, we analyzed two datasets using maximum likelihood and Bayesian inference methods: (1) two markers (ITS, trnL-F) of 285 Delphinieae species, and (2) six markers (ITS, trnL-F, trnH-psbA, trnK-matK, trnS-trnG, rbcL) of 32 Delphinieae species. All our analyses show that traditional Aconitum is not monophyletic and that subgenus Gymnaconitum and a broadly defined Delphinium form a clade. The SOWH tests also reject the inclusion of subgenus Gymnaconitum in traditional Aconitum. Subgenus Gymnaconitum markedly differs from other species of Aconitum and other genera of tribe Delphinieae in many non-molecular characters. By integrating lines of evidence from molecular phylogeny, divergence times, morphology, and karyology, we raise the mono- typic A. subg. Gymnaconitum to gener ic status.

The rise of angiosperm-dominated herbaceous floras: Insights from Ranunculaceae.

The rise of angiosperms has been regarded as a trigger for the Cretaceous revolution of terrestrial ecosystems. However, the timeframe of the rise angiosperm-dominated herbaceous floras (ADHFs) is lacking. Here, we used the buttercup family (Ranunculaceae) as a proxy to provide insights into the rise of ADHFs. An integration of phylogenetic, molecular dating, ancestral state inferring, and diversification analytical methods was used to infer the early evolutionary history of Ranunculaceae. We found that Ranunculaceae became differentiated in forests between about 108–90 Ma. Diversification rates markedly elevated during the Campanian, mainly resulted from the rapid divergence of the non-forest lineages, but did not change across the Cretaceous-Paleogene boundary. Our data for Ranunculaceae indicate that forest-dwelling ADHFs may have appeared almost simultaneously with angiosperm-dominated forests during the mid-Cretaceous, whereas non-forest ADHFs arose later, by the end of the Cretaceous terrestrial revolution. Furthermore, ADHFs were relatively unaffected by the Cretaceous-Paleogene mass extinction.

Evolution of Asian Interior Arid-Zone Biota: Evidence from the Diversification of Asian Zygophyllum (Zygophyllaceae)

The Asian interior arid zone is the largest desert landform system in the Northern Hemisphere, and has high biodiversity. Little is currently known about the evolutionary history of its biota. In this study, we used Zygophyllum, an important and characteristic component of the Asian interior arid zone, to provide new insights into the evolution of this biota. By greatly enlarged taxon sampling, we present the phylogenetic analysis of Asian Zygophyllum based on two plastid and one nuclear markers. Our phylogenetic analyses indicate that Asian Zygophyllum and Sarcozygium form a clade and Sarcozygium is further embedded within the shrub subclade. An integration of phylogenetic, biogeographic, and molecular dating methods indicates that Zygophyllum successfully colonized the Asian interior from Africa in the early Oligocene, and Asian Zygophyllum became differentiated in the early Miocene and underwent a burst of diversification in the late Miocene associated with the expansion of Asian interior arid lands due to orogenetic and climatic changes. Combining diversification patterns of other important components of the Asian interior arid zone, we propose a multi-stage evolution model for this biota: the late Eocene–early Oligocene origin, the early Miocene expansion, and the middle-late Miocene rapid expansion to the whole Asian interior arid zone. This study also demonstrates that, for Zygophyllum and perhaps other arid-adapted organisms, arid biomes are evolutionary cradles of diversity.

A molecular phylogeny of Dichocarpum (Ranunculaceae): Implications for eastern Asian biogeography.

East Asia is characterized by high levels of species diversity and endemism. However, the biogeographical patterns and processes underlying the distribution of biodiversity within the area are still poorly known. In this study, we used plastid (matK, trnL-F, and trnH-psbA) and nuclear (ITS) DNA sequences to investigate the historical biogeography of Dichocarpum (Ranunculaceae), an eastern Asian endemic genus throughout warm-temperate and subtropical forests of the area. Phylogenetic analyses strongly support Dichocarpum as monophyletic, which contains two major clades. Clade I corresponds to section Hutchinsonia, and clade II includes sections Dichocarpum and Fargesia. Section Dichocarpum and its subsections Dalzielia and Dichocarpum are not recognized as monophyletic. Our results suggest that the most recent common ancestor of Dichocarpum occurred in central China and Japan in the earliest Early Miocene, and thus support an ancient vicariance event between Japan and China. Within mainland China, three migrations at the species level were hypothesized to explain the expansion of Dichocarpum from central China to southeastern Yunnan, Hengduan mountains, and eastern Himalaya. These migration events occurred in the Late Miocene to Early Pliocene, which may be associated with the uplift of the southeastern Qinghai-Tibetan Plateau and accordingly the expansion of subtropical forests in China around that period. A migration or dispersal from central China to Taiwan was inferred in the Early Pleistocene, which supports the close floristic affinity between Taiwan and mainland China. This study contributes to our knowledge on the historical biogeography of plants in eastern Asia.