Qinghai-Tibetan Plateau is the worlds highest, and youngest plateau, known as "Roof of the World" or the "Earth Third Pole".It is located in the southwest, central and southern Asia at longitude 73°-104°, between 26°-39° latitude.The average elevation of the Plateau is more than 4500 m, with a total area of about 2.5 million km2, including the entire Qinghai province, Tibet and Sichuan provinces, province of Yunnan and some parts of Gansu and Xinjiang provinces.The severe climatic oscillations and orogenic activities of QTP must had an important effect on adaptive radiations, isolated evolution and speciation on the plateau biota.However, the effects of these climatic variability and land reforming phenomena in relation to speciation, range shifts and populations demography at QTP are largely unknown.Therefore, the QTP is becoming a biodiversity hot spot and model region for the research of phylogeography and speciation.Genus Spiraea L.is the most primitive genus in the deciduous group of sub family Spiroideae, family Rosaceae.Spiraea species are widely distributed at QTP and adjacent regions, with shrubby nature, constitute the alpine tundra ecosystem.In part first based on nineteen species of Spiraea a detailed investigation was carried out to find the genealogical histories among the species of Spiraea found on QTP and adjacent region.In the second part a total of 63 natural populations of two sister spiroides, S.alpina and S.mongolica were sampled to carry out their detailed comparative phylogeography.While in the last part nuclear ITS fragments were used to study the intraspecific divergence in S.alpina distributed on QTP and adjacent regions.　　1).Molecular Phylogenetics of Spiraea L species found on QTP and adjacent Regions.　　The Qinghai-Tibetan Plateau (QTP) and adjacent regions comprise an excellent mountainous system to study plant diversification and speciation within East-Asia.The uplift and eco-environmental processes of the QTP have had an obvious effect on organic evolution in the region.The present study addresses the relationship between speciation, diversification and geological events at this intense uplift.Sequence data from five plastid DNA regions (trnL-trnH, rpl2o-rpl12, rps15-ycf1, psbA-trnH, and trnS-trnG) and one nuclear ribosomal internal transcribed spacer of 19 species of the genus Spiraea were used in the study.Maximum parsimony and maximum likelihood trees were constructed in PAUP*, while divergence time was calibrated with BEAST v 1.7.5.Phylogenetic reconstruction revealed that these species form a single clade and can be divided into three sections.Diversification of Spiraea species began approximately 13.38 million years ago (MA) during the first stage of uplifting at the QTP.Diversification of Spiraea was further triggered and accelerated during the second stage of QTP uplifting in the last four million years.The estimated divergences time indicate that this rapid diversification was most likely triggered by the consecutive phases of QTP uplift in the early Pliocene, and accelerated during the Quaternary climatic oscillations.　　2).Comparative Phylogeography of Spiraea alpina and Spiraea mongolica.　　In this part comparative population genetic structure and historical demography of S.alpina and S.mongolica were carried out.These are closely related Spiroides shrubs distributed at the Qinghai-Tibetan plateau (QTP) with partial extension.Microsatellite data and chloroplast DNA (cpDNA) sequence data were obtained within 63 natural populations (S.alpina =497 individuals, S.mongolica =354 individuals) covering their entire geographical range on the QTP.The phylogenetic relationship implemented in Network and PAUP* based on three cpDNA haplotypes.Microsatellite data were clustered in STRUCTURE 2.2.3.Patterns of variation among and within populations were analyzed in Arliquin.Divergence time was calibrated in BEAST 1.7.5 with Sorbaria kirilowii fòssils.A total of 43 and 34 haplotypes based on cpDNA markers were identified in S.alpina and S.mongolica respectively.Phylogenetic tree clustered haplotypes of both species into two main groups and three lineages.The SSR data revealed three main clusters.Demographic analyses revealed population expansion events based on total chlorotypes in late Pleistocene.The SSR data revealed a high genetic diversity in both species.Our results suggested that high genetic diversity of these shrubs accredited to Pliocene and Pleistocene climatic changes, combined with orogenic activates of the QTR The distribution of these spiroides on the QTP resulted due to the combine effects of climatic instability during quaternary glacial-interglacial episodes and the uplifting of QTP.　　3).Intraspecific Divergence in Spiraea alpina (Rosaceae) inferred from nrDNA.　　In this part current study phylogeographic structure and diversification history ofS.alpina across the QTP were investigated for the first time based on nuclear internal transcribed spacer.The nuclear internal transcribed spacers (ITS1a-ITS4) were generated for a total of 284 individuals distributed within 31 natural populations.A clear phylogeographic structure was found for S.alpina.The results showed that this species colonized in three different glacial refugia during the Quaternary extensive glaciation and expanded during the Interglacial period.Analyses of molecular variance (AMOVA) showed 74.13 ％ genetic diversity among populations and 25.87 ％ genetic variation within populations with distinct phylogeographic structure (FST=0.741*).The estimated divergence time revealed that the main lineages of S.alpina diversified during the Quaternary 1.2-0.6 MA.The study concluded that severe climatic oscillations during Quaternary and the uplift of QTP had a profound effect on intraspecific divergence of S.alpina.