Abstract: Quaternary glacial climate oscillation and geographical isolation have significantly influenced the geographic distribution pattern and lineage evolution history of species. However, understanding how these factors specifically impact the genealogical structure of dominant Gramineous species in the Qinghai–Tibet Plateau (QTP) remains a subject of investigation. Elymus sibiricus L. (Gramineae), indigenous to the QTP and widely distributed in Eurasia, exhibits remarkable environmental adaptation and phenotypic diversity, making it an ideal candidate for phylogeographic studies. Based on the analysis of 175 complete chloroplast genome sequences, our results indicated that the ancestors of E. sibiricus originated from the QTP and underwent a complex migration history. After the speciation of E. sibiricus, several geo-groups exhibited independent differentiation, showing minimal gene flow among them. The current phylogeographic patterns of E. sibiricus are a result of frequent climate alternations and the cold climate during the Quaternary glacial, as well as the presence of several geographical barriers that have restricted the gene flow among different geo-groups. Our research has revealed for the first time that E. sibiricus has a multilineage origin, and its maternal donors are not limited to a single species. Furthermore, the high quality and mapping depth of the variant file provided reliable data for analyzing the patterns based on raw sequencing data. These findings enhance our understanding of the relationship between plant differentiation and climatic and geographical factors of Eurasia.

Key words: Elymus sibiricus,  Eurasia, geographical barrier, multilineage origin, phylogeography, Quaternary glaciation.