Speciation and biogeographical history in the European Alpine System: the radiation of Ranunculus sect. Euromontani (Ranunculaceae)

High mountain systems provide manifold preconditions for allopatric and sympatric speciation. We hypothesize that allopatric speciation due to geographical isolation of mountain chains, and sympatric speciation via allopolyploidy played major roles for a radiation within Ranunculus sect. Euromontani within the European Alpine System (EAS). We used target enrichment of 1249 nuclear gene loci on 81 samples for phylogenomics, biogeographical analysis, species delimitation, SNPs for genetic structure and NeighborNet analysis, flow cytometry for ploidy determination, and morphometrics for selected species pairs. We also included type material. The core R. sect. Euromontani comprises 12 monophyletic species, most of them (sub)endemic to one mountain system. The section originated probably from a widespread lineage and diversified 1.39 million years ago. Founder-event speciation was the most common mechanism; only one species (Ranunculus montanus) originated likely in situ via allopolyploidy. In the West Carpathians, the new species Ranunculus tatrimontanus was recognized as different from Ranunculus gruinalis (= Ranunculus pseudomontanus) in the South Carpathians. In the Pyrenees, clinal variation suggested inclusion of Ranunculus ruscinonensis into Ranunculus gouanii. Peripatric speciation during the Pleistocene was the predominant mechanism for this geographical/climatic radiation in the EAS, whereas sympatric speciation via allopolyploidy happened only in the Alps.