Molecular phylogeny and evolutionary history of Moricandia DC (Brassicaceae)

BACKGROUND: The phylogeny of tribe Brassiceae (Brassicaceae) has not yet been resolved because of its complex evolutionary history. This tribe comprises economically relevant species, including the genus Moricandia DC. This genus is currently distributed in North Africa, Middle East, Central Asia and Southern Europe, where it is associated with arid and semi-arid environments. Although some species of Moricandia have been used in several phylogenetic studies, the phylogeny of this genus is not well established. METHODS: Here we present a phylogenetic analysis of the genus Moricandia using a nuclear (the internal transcribed spacers of the ribosomal DNA) and two plastidial regions (parts of the NADH dehydrogenase subunit F gene and the trnT-trnF region). We also included in the analyses members of their sister genus Rytidocarpus and from the close genus Eruca. RESULTS: The phylogenetic analyses showed a clear and robust phylogeny of the genus Moricandia. The Bayesian inference tree was concordant with the maximum likelihood and timing trees, with the plastidial and nuclear trees showing only minor discrepancies. The genus Moricandia appears to be formed by two main lineages: the Iberian clade including three species, and the African clade including the four species inhabiting the Southern Mediterranean regions plus M. arvensis. DISCUSSION: We dated the main evolutionary events of this genus, showing that the origin of the Iberian clade probably occurred after a range expansion during the Messinian period, between 7.25 and 5.33 Ma. In that period, an extensive African-Iberian floral and faunal interchange occurred due to the existence of land bridges between Africa and Europa in what is, at present-days, the Strait of Gibraltar. We have demonstrated that a Spanish population previously ascribed to Rytidocarpus moricandioides is indeed a Moricandia species, and we propose to name it as M. rytidocarpoides sp. nov. In addition, in all the phylogenetic analyses, M. foleyi appeared outside the Moricandia lineage but within the genus Eruca. Therefore, M. foleyi should be excluded from the genus Moricandia and be ascribed, at least provisionally, to the genus Eruca.