Abstract: Taxonomy of Populus is a challenging task, especially in regions with complex topography, such as the Qinghai–Tibet Plateau because of the effect of hybridization, incomplete lineage sorting, phenotypic plasticity, and convergence. In the Flora of China, Populus pseudoglanca and Populus wuana are classified into sect. Leucoides and sect. Tacamahaca, respectively, but their taxonomy remains unclear. By conducting a systematic investigation for all taxa of Populus on the plateau, we found 31 taxa from the two sections. Through identification based on morphology and habitats, we confirmed that the “P. pseudoglanca” recorded in the Flora of Sichuan is not true P. pseudoglanca, while P. pseudoglanca and P. wuana recorded in the Flora of China may refer to the same species. By performing whole-genome re-sequencing of 150 individuals from the 31 taxa, we derived 2.28 million single nucleotide polymorphisms (SNPs). Further genetic and phylogenetic analyses demonstrated that the genetic structure of P. wuana is extremely consistent with P. pseudoglanca, and they all originate through the natural hybridization between Populus ciliata in sect. Leucoides and Populus curviserrata in sect. Tacamahaca. Our results suggested that P. wuana should be merged with P. pseudoglanca taxonomically. This study not only clarifies the taxonomic confusions related to P. pseudoglanca and P. wuana but also provides a new framework based on the integration of morphology, distribution, habitat, and genome to solve complex taxonomic problems.

Key words: Hybrid species, phylogeny, Populus, taxonomy, the Qinghai-Tibet Plateau