Eastward colonization of the Mediterranean Basin by two geographically structured clades: The case of Odontites Ludw. (Orobanchaceae)

• Ancient origin (ca. 18.9 Ma) but recent, intense diversification of Odontites s.l. (<5–6 Ma).
• Intense diversification is concomitant with major environmental events.
• Two geographically highly-structured clades.
• Eastward colonization of the Mediterranean Basin, from the Iberian Peninsula.

The biogeography of Mediterranean groups is very heterogeneous, because of the complex geologic and climatic history of the region. Our goal was to reconstruct the spatio-temporal history of the genus Odontites. In particular, we aimed to infer its area of origin and colonization routes, investigate its timing of diversification, and examine possible correlations with major environmental events. Based on sequencing of three chloroplast markers (psbA–trnH, trnL–trnF and trnC–ycf6), we reconstructed phylogenetic relationships among species. We performed molecular dating analyses (based on a large-scale rbcL dataset), ancestral areas reconstructions, and interpreted the observed patterns in the light of the complex geologic and climatic histories of the region. Our results suggested that Bartsiella and Bornmuellerantha should be reintegrated into Odontites s.l. The genus originated in the Iberian Peninsula ca. 18.9 Ma and diverged into two main clades 16.2 Ma, but species diversification was most intense <5–6 Ma. The two clades showed a clear geographic pattern: one clade originated in the Iberian Peninsula and Morocco, and extended its range to Eastern North Africa and the central Mediterranean Basin; the other clade originated in Europe and Western Asia, and mostly diversified within this ancestral area. The eastward colonization of the Mediterranean Basin contrasts with many other plant groups. Nevertheless, the burst of diversification in the Plio-Pleistocene agrees with what has been reported for other groups, and is concomitant with the end of the Messinian Salinity Crisis, onset of the Mediterranean climate and Quaternary glaciations. The link between phylogeny and geography suggests limited dispersal, and most dispersal events may have occurred overland rather than overseas.

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