Resolving the Taxonomic Enigma of Adonis in Eastern North China: An Integrated Phylogenomic Approach

The taxonomic identity of Adonis populations in eastern North China has long been controversial. Previous studies, relying on limited morphological data, have variably identified the Fuping (Hebei Province) population as A. ramosa, A. amurensis, or a subspecies of A. ramosa. To resolve this enigma, we conducted extensive field surveys and applied an integrated phylogenomic approach, utilizing genome skimming and RNA-seq data from 44 samples representing 10 Adonis species in China. Our analyses, based on both complete plastid genomes and nuclear single-copy orthologous genes, revealed that the Fuping population represents a distinct evolutionary lineage, which we describe as the new species A. fupingensis. In contrast, other populations from Beijing, Shandong, Henan, and Jiangsu were confirmed to belong to A. ramosa. We detected widespread gene tree discordance, primarily explained by incomplete lineage sorting (ILS), but also identified a clear case of ancient hybridization in the origin of A. sutchuenensis, with A. brevistyla and A. fupingensis as its parental donors. Despite the overall morphological similarity between A. fupingensis and A. ramosa, stable yet subtle differences in sepal and petal shape, root system architecture, and flowering phenology support their species-level distinction. This study highlights the critical need for phylogenomic data to disentangle complex evolutionary histories and clarify taxonomic disputes in morphologically challenging plant groups.