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A new species from the Qinghai-Tibetan Plateau is described and illustrated. Rhodiola yushuensis S.Y. Meng et J. Zhang sp. nov. is similar to Rhodiola smithii (Hamet) S. H. Fu, but it differs in its inner caudex leaves with obvious petioles and the leaf blades are obovate-triangular (vs. inner caudex leaves with strongly descends to the base of the petiole, and the leaves are long linear) and the outer caudex leaves are scalelike, triangular-suborbicular (vs. scalelike, narrowly triangular). Principal component analysis (PCA) analysis of the leaf traits and seed coat architecture also showed that R. yushuensis can be separated from R. smithii. The nrDNA internal transcribed spacer (ITS) sequences also support the claim that this plant is a new species, and it is grouped with R. smithii.

Sedum nanlingense (Crassulaceae), a new species from Guangxi, is described and illustrated here. We analyzed its morphological characteristics, which are largely similar to S. onychopetalum and S. kiangnanense. However, the morphology of this new species differs from other taxa in some important ways, including its 3-merous flowers, which contain six stamens and three carpels. Molecular phylogenetic analysis based on nuclear DNA internal transcribed spacer (ITS) sequences resolved S. nanlingense as a distinct clade, lending further support to its classification. Phylogenetic analysis showed that this new species is closely related to S. onychopetalum and S. kiangnanense.

Chrysanthemum bizarre (Asteraceae), a new species from Hunan Province, China, is described and illustrated. It is similar to Chrysanthemum vestitum in that its leaves are pubescent, and the ray florets are white. However, it differs from C. vestitum in that the abaxial pubescence of C. bizarre (6.5%) is much more sparsely appressed than that of C. vestitum (64.9%). The leaf blade is triangular ovate with its base extending downward on both sides of petiole to form wings. Only one capitulum, of which the outmost phyllaries are leaflike, develops at the tip of every flowering scape rather than forming an unconsolidated cyme synflorescence. In addition, the lectotype of C. vestitum was designated in this study.

There are two long‐standing biogeographic hypotheses regarding the glacial survival of plant species in the Qinghai–Tibetan Plateau (QTP): the in situ survival hypothesis and the tabula rasa hypothesis. We tested these two hypotheses in a phylogeographic study of Rhodiola sect. Prainia, a monophyletic section with ecologically divergent lineages. Molecular data from the nuclear internal transcribed spacer, six plastid markers and 13 nuclear microsatellite loci were analyzed for 240 individuals from 19 populations of this section. Environmental data were used to analyze the niches of major phylogenetic lineages within this section and to model changes in their distributions since the Last Glacial Maximum (LGM). We found that Rhodiola sect. Prainia consists of three evolutionary lineages: all populations of R. stapfii, R. prainii populations at the southern edge of the QTP, and R. prainii populations in the interior part of the QTP. During the LGM, the survival of R. prainii in the interior part of the QTP corresponded with the in situ survival hypothesis, while R. stapfii most probably survived the LGM in a manner corresponding with the tabula rasa hypothesis. The evolutionary history of different lineages of this section was shaped by topography, climate change, and lineage‐specific habitat preferences.

Rhodiola L. (Crassulaceae) is a mid-sized plant genus consisting of about 70 species, with most species distributed on the Qinghai-Tibetan Plateau (QTP) and the adjacent areas, and several species in north-east Asia, Europe, and North America. This study explored the origin and diversification history of Rhodiola and tested the biogeographic relationships between the QTP and other regions of the Northern Hemisphere. We sequenced the nuclear ribosomal internal transcribed spacers and eight plastid DNA fragments representing 55 species of Rhodiola, and reconstructed phylogenetic relationships with maximum parsimony, maximum likelihood and Bayesian inference. Several instances of incongruence between the nuclear and the plastid data sets were revealed, which can best be explained by reticulate evolution. Species of Rhodiola and Pseudosedum form a well-supported clade sister to Phedimus. Dating analysis suggested that the origin and diversification times of this group are largely correlated with the extensive uplifts of the Qinghai-Tibetan Plateau. Ancestral state reconstruction supports the hypothesis that Rhodiola originated on the QTP, and then dispersed to other regions of the Northern Hemisphere. Our findings highlight the importance of the uplifts of the Qinghai-Tibetan Plateau in promoting species diversification and the possible role of reticulate evolution in the diversification process. Our results also suggest the biogeographic significance of QTP as the source area in alpine plant evolution in the Northern Hemisphere.

The evolution and current distribution of the Sino-Tibetan flora have been greatly affected by historical geological events, such as the uplift of the Qinghai-Tibetan Plateau (QTP), and Quaternary climatic oscillations. Rhodiola kirilowii, a perennial herb with its distribution ranging from the southeastern QTP and the Hengduan Mountains (HM) to adjacent northern China and central Asia, provides an excellent model to examine and disentangle the effect of both geological orogeny and climatic oscillation on the evolutionary history of species with such distribution patterns. We here conducted a phylogeographic study using sequences of two chloroplast fragments (trnL-F and trnS-G) and internal transcribed spacers in 29 populations of R. kirilowii. A total of 25 plastid haplotypes and 12 ITS ribotypes were found. Molecular clock estimation revealed deep divergence between the central Asian populations and other populations from the HM and northern China; this split occurred ca. 2.84 million year ago. The majority of populations from the mountains of northern China were dominated by a single haplotype or ribotype, while populations of the HM harbored both high genetic diversity and high haplotype diversity. This distribution pattern indicates that HM was either a diversification center or a refugium for R. kirilowii during the Quaternary climatic oscillations. The present distribution of this species on mountains in northern China may have resulted from a rapid glacial population expansion from the HM. This expansion was confirmed by the mismatch distribution analysis and negative Tajima's D and Fu's F S values, and was dated to ca. 168 thousand years ago. High genetic diversity and population differentiation in both plastid and ITS sequences were revealed; these imply restricted gene flow between populations. A distinct isolation-by-distance pattern was suggested by the Mantel test. Our results show that in old lineages, populations may harbour divergent genetic forms that are sufficient to maintain or even increase overall genetic diversity despite fragmentation and low within-population variation.