Phylogenetic relationships and biogeography of Ranunculus and allied genera (Ranunculaceae) in the Mediterranean region and in the European Alpine System

Ranunculus s.l. shows a considerable species diversity and degree of endemism in the Mediterranean region and occurs with various life forms from the lowlands to the highest mountains. Based on a sampling from all continents, sequences of the ITS of nrDNA, the plastid matK, and the adjacent trnK regions were analysed using maximum parsimony and Bayesian inference. Both separate and combined analyses of the two datasets yielded a large core clade of Ranunculus excluding Ficaria, Coptidium, and the extraeuropean genera Beckwithia, Callianthemoides, Halerpestes, and Peltocalathos. The Ceratocephala-Myosurus-Glade is sister to the core Ranunculus in the plastid and the combined datasets on very long branches, thus supporting a classification of Ceratocephala and Myosurus as separate genera. Within Ranunculus s.s., eight well supported and highly consistent clades correspond either to widespread ecological groups (wetlands, high altitudes/latitudes) or to regional (mainly European) geographical groups. Alpine Mediterranean buttercups belong to orophytic Glades, most species of which also occur in the European alpine system; others show widespread northern hemisphere distributions. Only one Mediterranean clade is restricted to the Iberian Peninsula and adjacent regions. Present distribution patterns and molecular data support a hypothesis of an origin of alpine buttercups from lowland ancestors of the same geographical region. At lower altitudes, the predominant life forms, i.e., therophytes and geophytes, evolved multiple times suggesting parallel adaptations to the Mediterranean climate. Geophytes differentiated into an eastern and western Mediterranean group, and are most closely related to the subalpine, non-monophyletic "R. montanus" group, thus supporting a hypothesis of a common lowland ancestor. Tentative estimates for divergence times of the major clades in Ranunculus s.l. were made based on an age calibration for the Ranunculus-Xanthorhiza-split, using matK sequences and penalized likelihood analyses. The results from this study suggest that the split of allied genera from Ranunculus s.s. occurred during the Eocene and Oligocene, with the core clade of Ranunculus being c. 24.0 Myr old. Diversification of Ranunculus s.s. into main ecological/geographical clades took place in the late Miocene, and speciation within the Mediterranean groups during the Pliocene and Pleistocene. Diversification of life forms at lower altitudes occurred mainly during or after the establishment of the Mediterranean climate. Island endemics of Macaronesia and Crete are probably rather young descendents of neighbouring geographical groups. Diversification of alpine groups took place at different geological times, but is in general correlated with periods of colder climate. The high diversity of buttercups is likely a consequence of the broad spectrum of different habitats in the Mediterranean region.