Data from: Heteroploid Knautia drymeia (Caprifoliaceae) includes K. gussonei and cannot be separated into diagnosable subspecies

Premise of the study: Knautia drymeia is a morphologically variable, diploid and tetraploid temperate forest understory species distributed in southeastern Europe and adjacent areas. The species is an excellent system to explore the influence of polypoidy on taxonomic delineations, the role of hybridization among genetically distant populations in polyploid evolution, as well as the impact of glacial refugia on the evolution of polyploids. Methods: Amplified fragment length polymorphism fingerprinting and multivariate analyses of morphological characters were performed on 57 populations spanning the distribution area of K. drymeia. K-means clustering, comparison of in-silico tetraploids and observed tetraploids, and a phylogeographic analysis using relaxed random walks were used to explore the genetic structure within the diploids, to infer the origin of the tetraploids and to reconstruct range expansion through time. Further, we contrasted morphology and genetic groups with current taxonomy and evaluated the status of the tetraploid Apennine endemic K. gussonei and the intraspecific taxa of K. drymeia. Key Results: The genetic structure was strongly geographically correlated and yielded four genetic groups; K. gussonei was inseparable from K. drymeia. Distributions of diploid lineages are suggestive of glacial refugia in the northwestern-most and southeastern Balkan Peninsula. Polyploids originated at least two times, as autopolyploids and probably additionally also as allopolyploids. Morphological divergence corresponded with neither genetic groups nor current taxonomy. Conclusions: Genetic and morphometric data neither confirmed divergence of K. gussonei nor recognition of subspecies within K. drymeia. We therefore propose treating K. drymeia as morphologically and genetically variable species without infraspecific taxa.