Taxonomic identity and associated revisions of Populus szechuanica var. tibetica

The genus Populus represents one of the most taxonomically challenging plant groups, with P. szechuanica var. tibetica standing out as a typical representative of such taxonomic perplexity. Extensive taxonomic confusion surrounding this variety involves a multitude of related taxa, which has imposed considerable adverse impacts on the research and utilization of poplar species. In this study, we conducted a long‐term systematic investigation integrating literature review, herbarium specimen examination, morphological analysis, distribution survey, genomic sequencing, and growth trait observation, which has clarified most of the existing taxonomic ambiguities and led to the description of a new species. The fundamental cause of the persistent taxonomic confusion is that the multiple syntypes assigned to P. szechuanica var. tibetica do not belong to a single species: the syntypes collected from Ladakh exhibit distinct morphological characteristics of P. ciliata , while the syntype from western Sichuan is a member of the P. szechuanica species complex. Poplar taxa previously identified as P. szechuanica var. tibetica show remarkable discrepancies in morphology, genetics, habitat adaptation, and phylogenetic relationships. Our findings confirm that P. yatungensis , P. pseudoglauca , and P. wuana originate from natural hybridization between P. ciliata var. gyirongensis and P. curviserrata , whereas P. purdomii , P. xiangchengensi s, and P. haoana derive from natural hybridization between P. szechuanica and P. curviserrata . We therefore propose the following taxonomic treatments: P. szechuanica var. tibetica and P. yatungensis should be recognized as two independent varieties of P. ciliata , and P. purdomii , P. xiangchengensis , and P. haoana should be reduced to the rank of variety under P. szechuanica . Additionally, the native poplar from the middle reaches of the Yarlung Tsangpo River, putatively derived from natural hybridization among P. ciliata , P. cathayana , and P. curviserrata , is described here as a new species, P. yinii .