Long neglected diversity in the Accursed Mountains (western Balkan Peninsula): Ranunculus bertisceus is a genetically and morphologically divergent new species

Southern European mountain ranges have long been recognized as important hotspots of genetic diversity and areas of high endemism. Reflecting the geographical complexity of these mountain ranges, many European high-mountain species exhibit disjunctions on a variety of geographical scales. One of the long-neglected, poorly investigated and unresolved taxonomic problems concerns Apennine and Balkan members of Ranunculus section Leucoranunculus. According to the most recent taxonomic treatment, this section includes Ranunculus crenatus, distributed predominantly in siliceous massifs of the Carpathians and the Balkan Peninsula, but with a highly disjunct partial distribution area in the eastern Alps, and Ranunculus magellensis, which is usually considered a calcicolous endemic of the central Apennines. However, R. magellensis has also been suggested to occur in the carbonate ranges of the Albanian Alps, which would render this species amphi-Adriatic. We used complementary molecular methods (sequences of the nuclear ribosomal ITS region and of plastid DNA and amplified fragment length polymorphisms), relative genome size measurements and morphometric analyses to elucidate the relationships in Ranunculus section Leucoranunculus. Specifically, we asked if it comprises only a single, widespread and morphologically variable species or several narrowly distributed species with constant morphology. The results of our study showed that populations growing on limestone in the Albanian Alps in northern Albania and southern Montenegro are divergent and should be recognized as a new species, Ranunculus bertisceus Kuzmanović, D.Lakušić, Frajman & Schönsw., sp. nov. These populations differ not only from R. crenatus s.s., which grows on silicates, but also from the calcicolous Apennine endemic R. magellensis. The eastern Alpine populations of R. crenatus, which occur very locally in the Niedere Tauern area, originate from immigration from the Bosnian mountains.