Phylogeny, diversification and biogeographic implications of the eastern Mediterranean endemic genus Ricotia (Brassicaceae)

Abstract

Ricotia (Brassicaceae) is a genus of nine species endemic to the eastern Mediterranean region. Its phylogenetic relationships, monophyly, and tribal placement have not yet been adequately addressed. To achieve this, sequence data from the nuclear-encoded ribosomal internal transcribed spacer (ITS) and chloroplast DNA (trnL-F region) were analysed by parsimony, maximum likelihood, and Bayesian methods for 45 Ricotia accessions, representing all species and covering their entire distribution ranges, along with outgroups of selected members of main Brassicaceae lineages and tribes. The results clearly indicate, with high posterior probability/bootstrap support, that Ricotia is monophyletic and together with Lunaria should be assigned, with Biscutella and Megadenia, to tribe Biscutelleae. Divergence time estimations, using both a secondary calibration approach and published ITS substitution rates, indicate that the origin of Ricotia (crown group age, 9.2-11.3 Ma) predates the onset of the Mediterranean climate after the Messinian Salinity Crisis (5.9-5.3 Ma). We tentatively conclude that diversification within Ricotia was affected by climate changes during that geological epoch which had a great impact on the speciation history of the Mediterranean flora and fauna. Ancestral area reconstruction analyses revealed that Mediterranean Ricotia species arose in southwest Anatolia (likely Antalya region), whereas the origin of the genus remained unclear. Finally, a perennial life cycle appears to be ancestral in Ricotia, as revealed by an ancestral character state reconstruction analysis.