Amphi-Adriatic distributions in plants revisited: Pleistocene trans-Adriatic dispersal in the Euphorbia barrelieri group (Euphorbiaceae)

Abstract

Several plant and animal species exhibit amphi-Adriatic distributions spanning the Italian and Balkan peninsulas. Such distribution patterns have traditionally been explained mostly by land connections between the two peninsulas during the Messinian salinity crisis (Miocene/Pliocene), but recent studies employing molecular dating pointed to more recent, i.e. Pleistocene, dispersals from the Balkans to Italy. One of the plant groups exhibiting such a distribution pattern is the Euphorbia barrelieri group (Euphorbiaceae), in which six taxa (variously treated as species or subspecies) have been traditionally included. We employed AFLPs and nuclear (ITS) and plastid (trnT-trnL) DNA sequences to disentangle relationships among them and infer their spatio-temporal diversification. Our results clearly show that E. hercegovina and E. saxatilis do not belong to the group, which thus consists of four species. The common ancestor of the E. barrelieri group originated and diversified in the Pleistocene, giving rise to E. barrelieri distributed in Italy and France on one side of the Adriatic and E. kerneri in the south-eastern Alps and E. triflora and E. thessala on the Balkan Peninsula on the other side. Phylogeographical analysis inferred a trans-Adriatic dispersal of the lineage leading to E. barrelieri from the Balkan Peninsula, thus underlining the importance of this area for the origin of Italian biota. Last but not least, E. hercegovina subsp. javoriensis is clearly nested in E. triflora. Based on our results we provide a taxonomic treatment of all four species and designate five lectotypes.