Polyploids recurrently emerge in angiosperms, but most polyploids are likely to go extinct before establishment due to minority cytotype exclusion, which may be specifically a constraint for dioecious plants to evolve polyploid populations. Investigations into the frequency and distribution of polyploids in natural populations is thus necessary for understanding polyploid evolution in plants. This study determined the ploidy levels of 28 populations and 351 individuals of Salix polyclona, and identified the type of polyploidy (auto- vs. allo-) using whole genome re-sequencing data. We further investigated the phylogeny, population genetic diversity and species range shifts to explore the origin and spatiotemporal evolution of the polyploid complex. Our analyses revealed a high frequency (52%) of autopolyploids in it with a clear geographic distribution confined to the western part of its range where complex mountain systems create higher levels of environmental heterogeneity. Comparisons of diploid male and female genomes suggested a female heterogametic sex-determining factor on chromosome 15, which likely also acts in the dioecious polyploids. Fossil-calibrated phylogeny showed a more recent diversification of the polyploids (ca. 2.3 Ma) than the diploid (ca. 6.2 Ma), and population demographic histories largely corroborated the geological and climatic history of the region. Our results suggest that climatic oscillations and uplift of eastern Qinghai-Tibetan Plateau and the connecting mountains may have facilitated the preservation and establishment of polyploid populations. This study provides an example of the evolution of a diploid-polyploid complex in a willow species and illustrates a role of polyploidization in mountain biodiversity.

Species of Elaeocarpaceae vary, but complete chloroplast genome data and systematic comparisons across the family are rarely reported. To understand the variation in chloroplast sequence size and structure in Elaeocarpaceae, the chloroplast genomes of 9 species were sequenced using the Illumina HiSeq 2000 platform and further assembled and annotated with Elaeocarpus japonicus and Sloanea sinensis (family Elaeocarpaceae) as references. A phylogenomic tree was constructed based on the complete chloroplast genomes of the 11 species representing 5 genera of Elaeocarpaceae. Chloroplast genome characteristics were examined by using Circoletto and IRscope software. The results revealed the following: (a) The 11 sequenced chloroplast genomes ranged in size from 157,546 bp to 159,400 bp. (b) The chloroplast genomes of Elaeocarpus, Sloanea, Crinodendron and Vallea lacked the rpl32 gene in the small single-copy (SSC) region. The large single-copy (LSC) region of the chloroplast genomes lacked the ndhK gene in Elaeocarpus, Vallea stipularis, and Aristotelia fruticosa. The LSC region of the chloroplast genomes lacked the infA gene in Elaeocarpus and Crinodendron patagua. (c) Through inverted repeat (IR) expansion and contraction analysis, a significant difference was found between the LSC/IRB and IRA/LSC boundaries among these species. Rps3 was detected in the neighboring regions of the LSC and IRb regions in Elaeocarpus. (d) Phylogenomic analysis revealed that the genus Elaeocarpus is closely related to Crinodendron patagua on an independent branch and Aristotelia fruticosa is closely related to Vallea stipularis, forming a clade with the genus Sloanea. Structural comparisons showed that Elaeocarpaceae diverged at 60 Mya, the genus Elaeocarpus diverged 53 Mya and that the genus Sloanea diverged 0.44 Mya. These results provide new insight into the evolution of the Elaeocarpaceae.

How and why species range size varies along spatial gradients is fundamental yet controversial topics in biogeography. To advance our understanding on these questions and to provide insight into biological conservation, we assessed the elevational variations in vascular plants range size for different life form and biogeographical affinities, and explored the main drivers underlying above variations in the longest valley in China's Himalayas---the Gyirong Valley. Elevational range sizes of vascular plants were documented by 96 sampling plots along 12 elevational bands of 300-m ranging from 1800 to 5400 m above sea level. We assessed the elevational variations in range size by averaging the range size of all species within each elevational band. We then related range size to climate, disturbance, competition factors and the mid-domain effect, and explored the relative importance of aforementioned factors in explaining the range size variations using the Random Forest model. Total 545 vascular plants were documented by our sampling plots along the elevational gradient. Out of 545 plants, 158, 387, 337 and 112 were woody, herbaceous, temperate and tropical species respectively. Range size of each groups of vascular plants shown uniform increasing trends along the elevational gradient which are in accordance with the prediction of Rapoport's rule. Climate was the main driver for the increasing trends of vascular plants range size in the Gyirong Valley. Climate variability hypothesis and mean climate condition hypothesis were both supported to jointly explain such climate-range size relationship. Our results reinforce previous notion that Rapoport's rule applies to where the influence of climate is most pronounced, and call for close attention to the impact of climate change in order to prevent range contraction and even extinction under global warming.