The origin and evolution of alpine floras potentially can be shaped by immigration via long-distance dispersal or migration over mountain chains. Alternatively, origins of alpine species may be referred to regional speciation via origins from lowland ancestors and adaptation to high altitudes. Moreover, evolutionary histories of alpine species have also been influenced by Quaternary glaciations. Range fluctuations due to climatic oscillations have caused vicariant speciation and secondary con- tact hybridization. However, comparative phylogenetic studies on alpine floras from mountain systems of different continents are scarce. Here we review the phylogenetic relationships of alpine species of Ranunculus, an almost cosmopolitan genus with alpine representatives in all major mountain systems of the world. Based on molecular phylogenetic analysis of 245 alpine and lowland species (based on a combined dataset of ITS, matK, trnK and psbJ-petA sequences), we try to elucidate origins of alpine buttercups. Results suggest that most major mountain systems (European Alpine System, Irano-Turanian mountains, Himalayas, Central Asian mountains, African mountains, and Andes) have been colonized multiple times independently; only the North American alpine species fall all into one clade. In the European and Irano-Turanian mountains, recruitment of alpine species from lower altitudes of the same area, and migration within the Tethyan area might have played a major role. The alpine species of the Himalayas, the Central Asian mountains, the North American alpine species and the Arctic species fall into another, distinct clade, which may suggest a northern migration route. The North American alpine clade comprises many lowland species and might have diversified via adaptive radiation. In contrast, the Himalayan species have no lowland source flora and might have originated from immigrants of the Central Asian mountains. Tropical alpine Ranunculi in the mountains of Eastern Africa and in Taiwan have originated after long-distance dispersal from other continents. The origin of the New Zealand alpines could have been referred to long-distance dispersal, probably following southern migration routes via the Antarctic and South America. The Andes have been colonized multiple times by related genera of Ranunculus. We conclude that autochthonous origins and regional diversification of buttercups play a major role in northern hemispheric mountain systems, where alpine species could have evolved from rich lowland source floras. In subtropical to tropical mountain systems, and in the Southern Hemisphere, alpine species have been rather recruited via immigration, including long-distance dispersal from other continents. A high adaptive potential of Ranunculus to alpine habitats might have helped to evolve alpine species all over the world.
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