The numerous disjunct plant distributions between Macaronesia and eastern Africa-Arabia suggest that these could be the relicts of a once continuous vegetation belt along the southern Tethys, which has been fragmented by Upper Miocene-Pliocene aridification. We tested this vicariance hypothesis with a phylogenetic analysis of Campylanthus (Plantaginaceae), based on nuclear and plastid DNA sequence data. Our results indicate a basal split within Campylanthus giving rise to Macaronesian and Eritreo-Arabian lineages in the Pliocene/Upper Miocene. This is consistent with the vicariance hypothesis, thus obviating the need to postulate trans-Saharan long-distance dispersal. The biogeography of Campylanthus may parallel patterns in other plant groups and the implications for our understanding of the biogeography of northern and eastern Africa, and Arabia are discussed.
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