Phylogenetic and phylogeographic analysis of the western Mediterranean Arenaria section Plinthine (Caryophyllaceae) based on nuclear, plastid, and morphological markers

Abstract

Arenaria sect. Plinthine is an easily distinguishable morphologically cohesive group encompassing 14 species and five additional subspecies. To explore phylogenetic relationships and search for phylogeographic patterns in a group that is restricted to the western Mediterranean, independent and combined analyses of four datasets (morphological characters and sequences from nuclear and plastid DNA: nrITS, trnT-trnL, trnL-trnF) were conducted using Maximum Parsimony, Neighbour-Joining, Maximum Likelihood and Bayesian Inference. Monophyly of the section is supported by the data, the ITS sequences show full agreement with taxonomy for one third of the taxa, and the high number of trnL-F haplotypes found in SE Spain (7 of 11) is consistent with the fact that this region is one of the hotspots of biodiversity in the Mediterranean. However, a number of less easily interpretable results have been obtained, despite considerable ITS variation (43 parsimony informative characters within the ingroup) and a reasonable intraspecific sampling for this marker. These results are: low resolution at deep nodes of the ingroup, partial discordance between taxonomy and ITS sequences particularly for widespread taxa, and lack of congruence not only between the topologies of the plastid and nuclear trees but also between the two plastid trees. It is proposed that a combination of factors (rampant aneuploidy, polyploidy, hybridization, lineage sorting, and concerted evolution of ITS sequences) are responsible for the incongruent but not totally unexpected results.