Combining nuclear genome, chloroplast fragments and morphology to solve the species delimitation of Aquilegia incurvata (Ranunculaceae)
Hybridization can be widespread among closely related plant species, and the resulting intermediate traits may complicate species delimitation and identification. Such taxonomic uncertainty can lead to misinformed conservation actions or poor resource management. Aquilegia incurvata is a Chinese endemic species restricted to the Qinba Mountains. Despite numerous field surveys in its reported distribution area, over a five-year period, no specimens fitting its description in “Flora Tsinlingensis” have been found, casting doubts on the validity of this species. To determine whether A. incurvata truly exists, we examined the type specimens of A. incurvata (including holotype and paratypes), as well as fresh material from four populations of Aquilegia occurring at the type locality. We also conducted morphological and genetic analyses to explore species boundaries between A. incurvata and four closely related species (A. ecalcarata, A. kansuensis, A. yabeana and A. yangii). Additionally, we integrated morphological and genetic data from 12 previously reported populations of these four closely related species. We performed morphological clustering via principal component analysis (PCA), as well as phylogenetic and population genetic analyses. Eleven floral traits from six type specimens and four populations were quantified for interspecific differentiation. Strict filtering of whole-genome resequencing data yielded 9,073 high-quality SNPs and 20 cpDNA loci from A. incurvata’s type specimens and its closely related species. Our study revealed two key findings: (1) The type specimens of A. incurvata are hybrids between A. kansuensis, A. yangii and A. ecalcarata, with genetic components of all three species and floral morphology intermediate between A. kansuensis and A. yangii; (2) Samples from the locus classicus and the provenances of the paratype specimens of A. incurvata cluster into two groups—One corresponds to A. yabeana and the other one to A. kansuensis. Our study confirms A. incurvata is not an independent species but a local hybrid.
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