Phylogeny and evolutionary history of alpine alkali grasses (Poaceae: Puccinellia) within the subtribe Coleanthinae

Alkali grasses (Poaceae: Puccinellia) are a widely-distributed and species-rich group that has developed tolerance to alkaline and/or saline conditions. With more than 100 species, the genus is the largest in the subtribe Coleanthinae and is characterized by the ubiquity of polyploidy and hybridization. Despite large taxonomic and ecological diversity, the evolutionary history of alkali grasses and the emergence of their high-mountain diversity remain poorly understood. In this study, we combined genomic data (DArTseq), nuclear ribosomal, and chloroplast markers to shed more light on the origins of alpine alkali grasses within the subtribe Coleanthinae. Using a global perspective, we found that the alpine species of the Pan-Tibetan Highlands emerged at different timescales along the evolutionary history of Puccinellia. Particularly, our results revealed that two high-alpine species, P. pamirica and P. subspicata, are resolved near the backbone of the infrageneric diversification of alkali grasses and remain closely related to multiple arctic species. Our integrative approach suggests a key role of cold-tolerance during the early stages of evolutionary radiation of the genus and highlights the importance of the Pleistocene climate oscillations for speciation in alkali grasses.