Evolutionary response to the Qinghai-Tibetan Plateau uplift: phylogeny and biogeography ofAmmopiptanthusand tribe Thermopsideae (Fabaceae)

Abstract

Previous works resolved diverse phylogenetic positions for genera of the Fabaceae tribe Thermopsideae, without a thoroughly biogeography study. Based on sequence data from nuclear ITS and four cpDNA regions (matK,rbcL,trnH-psbA,trnL-trnF) mainly sourced from GenBank, the phylogeny of tribe Thermopsideae was inferred. Our analyses support the genera of Thermopsideae, with the exclusion ofPickeringia, being merged into a monophyletic Sophoreae. Genera of Sophoreae were assigned into the Thermopsoid clade and Sophoroid clade. Monophyly ofAnagyris,BaptisiaandPiptanthuswere supported in the Thermopsoid clade. However, the genera Thermopsis and Sophora were resolved to be polyphyly, which require comprehensive taxonomic revisions. Interestingly,Ammopiptanthus, consisting ofA. mongolicusandA. nanus, nested within the Sophoroid clade, withSalweeniaas its sister.AmmopiptanthusandSalweeniahave a disjunct distribution in the deserts of northwestern China and the Hengduan Mountains, respectively. Divergence age was estimated based on the ITS phylogenetic analysis. Emergence of the common ancestor ofAmmopiptanthusandSalweenia, divergence between these two genera and the split ofAmmopiptanthusspecies occurred at approximately 26.96 Ma, 4.74 Ma and 2.04 Ma, respectively, which may be in response to the second, third and fourth main uplifts of the Qinghai-Tibetan Plateau, respectively.