Taxonomy and biogeography ofDiapensia(Diapensiaceae) based on chloroplast genome data

DiapensiaL. is the second largest genus of Diapensiaceae. The taxonomic treatment withinDiapensiaand relationships within Diapensiaceae have been disputed. Chloroplast genome sequence data have proved to be useful for plant phylogenetic analyses and species delimitation. In this study, we de novo sequenced and assembled 22 chloroplast genomes of 15 species of Diapensiaceae, including all recognized species ofDiapensiawith multiple samples. A super-matrix containing a total of 107 genes and 18 taxa was constructed for phylogenetic analyses to resolve phylogenetic relationships among genera of the family and withinDiapensia. The resulting phylogenetic tree showed the following strongly supported relationships: (Galax, (Pyxidanthera, (Berneuxia, ((Schizocodon, Diapensia), andShortia s.s.)))). The dated phylogeny and reconstructed lineage-through-time plot for the family indicated rapid diversification in the Neogene and an acceleration of diversification rate after c. 8 Ma. Biogeographic analysis suggested thatDiapensiaoriginated in the Northeast Asian mountains approximately 6.06 Ma, followed by northward dispersal to the Arctic and southwestward dispersal to the Himalaya-Hengduan Mountains. Phylogenetic relationships withinDiapensiawere well resolved. Based on the phylogenetic results, we proposed to reinstate the species status ofDiapensia bulleyanaForrest ex Diels, and raisedD. purpureaf.albidato the species rank (D. albida[W. E. Evans] J. F. Ye comb. & stat. nov.). The distribution ranges of all species delineated based on the phylogenetic results were revised accordingly based on specimen occurrences. Our study adds new examples for the power of plastid genome data for resolving phylogenetic relationships and clarifying taxonomic disputes among closely related species.