Abstract
Species delimitation in the genus Populus is particularly challenging due to high levels of intraspecific polymorphism as well as frequent interspecific hybridisation and introgression. In this study, we aimed to examine the taxonomic status of Populusningshanica and P.wulianensis using an integrative taxonomy that considers multiple operational criteria. We carried out morphometric analyses of leaf traits and genetic examinations (including sequence variations at five barcoding DNAs and polymorphisms at 14 nuclear microsatellite SSR primers) at the population level between them and two closely related species P.adenopoda and P.davidiana. Results suggest that P.wulianensis belongs to the polymorphic species, P.adenopoda and should be considered as a synonym of the latter. P.ningshanica may have arisen as a result on the hybridisation between P.adenopoda and P.davidiana and therefore should be treated as P.×ningshanica. This study highlights the importance of the integrated evidence in taxonomic decisions of the disputed species.