Phylogenetic evidence for a Miocene origin of Mediterranean lineages: species diversity, reproductive traits and geographical isolation

A review of 27 angiosperm clades (26 genera) of species-rich and species-poor plant groups of the Mediterranean floristic region was performed with phylogenetic and biological trait data. The emergent pattern is that a majority of Mediterranean plant clades split from their sister groups between the Miocene (23-5 Ma) and the Oligocene (34-23 Ma), far earlier than the onset of the Mediterranean climate (ca. 3.2 Ma). In addition, 12 of 14 clades of the species-poor group have stem ages inferred for each clade in the Miocene or older, and six of 13 clades within the species-rich group show divergence of each stem clade within the Oligocene and/or Miocene. High levels of species diversity are related to an ancient (Paleocene-Miocene) origin and also to recent origin (Pliocene-Pleistocene) followed by active speciation and even explosive radiations: some species and lineages diversified over a short period (Aquilegia, Cistus, Dianthus, Linaria sect. Supinae, Reseda). In the species-rich group, key reproductive characters were found to be significantly more important for species recognition than key vegetative characters in eight clades, but no difference was found in four clades, and vegetative characters were predominant in one clade (Saxifraga). Geographical differentiation is proposed as predominant over divergence driven by pollination ecology. We hypothesise an evolutionary process in which lineages adapted to pre-Mediterranean (pre-Pliocene) conditions in relatively small, xeric areas became strongly competitive and expanded as the Mediterranean climate became dominant (Pliocene-Quaternary) across the Mediterranean Basin.