Molecular phylogeny and biogeography of the bipolar Euphrasia (Orobanchaceae): recent radiations in an old genus

Abstract

Euphrasia includes perennial or annual green parasitic plants, and has a disjunct bipolar distribution except for one transtropical connection across the high mountains of Oceania. The disjunction is coupled with strikingly contrasting patterns of morphological diversity between the southern and northern hemispheres, making it an exciting model to study processes of evolutionary diversification which shaped present floras. We inferred the relationships among 51 species representing 14 of the 15 sections of the genus based on nrDNA ITS and cpDNA trnL intron, trnL-trnF and atpB-rbcL intergenic spacers. Maximum parsimony and Bayesian inference support monophyly of the genus and of several intrageneric groups characterized by morphology, ploidy level, and geographic range. Molecular phylogenetic dating using Bayesian "relaxed" clock methods suggests that the earliest Euphrasia radiations occurred minimum 11-8 Mya with bipolarity being achieved 7-5 Mya. Biogeographic analyses using explicit model-based approach inferred Eurasia as an ancestral area for the genus. The most parsimonious reconstruction found by a dispersal-vicariance analysis requires 17 dispersals to account for the current biogeographic pattern and supports Eurasian origin for Euphrasia. Both long-distance dispersal and across land vicariance can be invoked to explain the diversification in the genus, which experienced rapid radiations driven by new ecological opportunities of the late Pliocene and Pleistocene but also retained a set of local endemic or relict species of an earlier origin.