Taxonomy and Reticulate Phylogeny of Heliosperma and Related Genera (Sileneae, Caryophyllaceae)

Heliosperma (nom. cons prop.) comprises 15—20 taxa, most of them endemic to the Balkan Peninsula. DNA sequences from the chloroplast (rps16 intron, psbE-petG spacer) and the nuclear genome (ITS and four putatively unlinked RNA polymerase genes) are used to elucidate phylogenetic relationships within Heliosperma, and its position within Sileneae. Three main lineages are found within Heliosperma: Heliosperma alpestre, H. macranthum and the H. pusillum-clade. The relationships among the lineages differ between the plastid and the nuclear trees. Relative dates are used to discriminate among inter- and intralineage processes causing such incongruences, and ancient homoploid hybridisation is the most likely explanation. The chloroplast data strongly support two, geographically correlated clades in the H. pusillum-group, whereas the relationships appear poorly resolved by the ITS data, when analysed under a phylogenetic tree model. However, a network analysis finds a geographic structuring similar to that in the chloroplast data. Ancient vicariant divergence followed by hybridisation events best explains the observed pattern. The morphological and taxonomical diversity in the H. pusillum-group is possibly ecology-induced, and is not correlated with the molecular data. Phylogenetic patterns regarding the origin of Heliosperma are complicated, probably influenced by reticulate and sorting events. At least two ancient lineages have been involved in its evolution, one most closely related to Viscaria/Atocion and the other to Eudianthe/Petrocoptis. Atocion and Viscaria are sister genera, most species-rich on the Balkans, and including six/three species. Phylogenies do not support their traditional classification, and provide a framework for a taxonomic revision. Atocion compactum is found in three different positions in the chloroplast tree, and in a single clade in the nuclear gene trees. Using relative dates we demonstrate that hybridisation with subsequent chloroplast capture is a feasible explanation for the pattern observed. This, and other observed reticulate patterns, highlights the importance of hybridisation in plant evolution