Large-scale patterns of biodiversity and the underlying mechanisms that regulate these patterns are central topics in biogeography and macroecology. The Qinghai-Tibetan Plateau (QTP) is a natural laboratory for studying these issues. However, most previous studies have focused on the entire QTP, and the independent physical geographical subunits in the region are not well understood. We studied the current plant diversity on the Kunlun Mountains, an independent physical geographical subunit located in northwest China, on the northern edge of the QTP. We integrated measures of species distribution, geological history, and phylogeography, and analyzed the taxonomic richness, origin time, and community phylogenetic structure of the plants present in the area. The distribution patterns of 1,911 seed plants highlighted that species were located mainly in the eastern regions of the Kunlun Mountains. Chinese endemic species of seed plants accounted for 29.8% of the total species on the Kunlun Mountains. The biodiversity patterns and mean divergence times (MDT) indicated that the eastern region of the Kunlun Mountains was the center for biodiversity conservation, particularly in the southeastern region, which has served as a museum for plant diversity on the Kunlun Mountains. According to the MDT, the origin time of the Kunlun Mountains’ flora (KMF) was early Miocene (19.40 Ma), and the KMF is ancient. The biogeographical roles of the Kunlun Mountains were corridor and sink, and the corresponding key processes were species immigration and extinction. The extant biodiversity on the Kunlun Mountains has occurred through species recolonization after climatic fluctuations and glaciations during the Quaternary. The Kunlun Mountains also formed a barrier, representing a boundary among multiple floras, and converted the QTP into a closed physical geographical unit. The nearest taxon index indicated that habitat filtering may have played an important role in biodiversity patterns.

Biodiversity and community assembly are central topics in ecological studies, and mountains present natural laboratories for studying these issues. Most previous studies have focused on biodiversity hotspots and tropical regions, and relevant research in the middle and high latitudes is relatively limited. We hypothesized that species dispersion and habitat filtering simultaneously might drive the assembly of the current plant community in temperate region mountains. We studied the plant community of the Kunlun Mountains, an independent physical geographic unit located in northwest China on the northern edge of the Qinghai-Tibetan Plateau. We integrated measures of species distribution, geological history, and phylogeography, and analyzed the taxonomic richness, phylogenetic diversity, and phylogenetic community structure of the current plant community in the area. The distribution patterns of 1,911 seed plants showed that species were distributed mainly in the eastern and the southeastern parts of the Kunlun Mountains, which were considered as conservation targets for biodiversity. Similarities of genera and species strongly indicated that mass species migrations exist among the Kunlun Mountains and adjacent biodiversity hotspots. This indicated that the current patterns of species diversity were from species recolonization, and the plant species of the Kunlun Mountains originated primarily from the Hengduan Mountains which are a biodiversity hotspot. The net relatedness index (NRI) indicated that 17 of the 28 communities were phylogenetic clustering, and the others were phylogenetic dispersion. The nearest taxon index (NTI) indicated that 27 of the 28 communities were phylogenetic clustering, and the phylogenetic community structure of Banma County was the only example of overdispersion. By combining the standard effect size phylogenetic diversity (SES-PD) with the two indexes, we showed that species recolonization was likely to be an important evolutionary process affecting the assembly of current plant communities, and that habitat filtering may have drove the ecological processes of these communities.