Disentangling relationships among the members of the Silene saxifraga alliance (Caryophyllaceae): Phylogenetic structure is geographically rather than taxonomically segregated

Out of ca. 700 species belonging to Silene, 15 to 35 were classified in S. sect. Saxifragoideae. This section has its highest diversity on the Balkan Peninsula, which was the most important European Pleistocene refugium. The most widespread of the species is S. saxifraga ranging from the Pyrenees to the Carpathians. Together with ten morphologically similar taxa it is often treated as the S. saxifraga group, but the relationships among the taxa are unclear and blurred due to the occurrence of transitional forms. In this study, we used sequences of the nuclear ribosomal internal transcribed spacer (ITS) and the plastid rps16 intron as well as amplified fragment length polymorphisms (AFLPs) to elucidate phylogenetic relationships among the taxa belonging to—or hypothesized to be closely related to—S. sect. Saxifragoideae, covering the section’s entire geographical range. Phylogenetic analyses of 112 populations belonging to 33 taxa clarified previous classifications and showed that S. cephallenia, S. congesta, S. linoides, S. multicaulis, S. schwarzenbergeri and S. waldsteinii are clearly differentiated from all other taxa, which in turn form the newly circumscribed S. saxifraga group. Phylogenetic relationships within the latter are unresolved, and are governed by geographic proximity rather than by taxonomic identity. This is likely a result of recent rapid radiation and range expansion, as well as of convergent morphological evolution triggered by similar environmental selection pressures. The southern parts of the Balkan Peninsula are the centre of genetic diversity of the group, underlining the area’s importance as a sanctuary of diversification of European biota.