Evolution of the European high mountain flora

Sempervivum tectorum (Houseleek), a mountain plant of rocky habitats, is widespread in the European high mountains, but also grows in rocky habitats of the Rhine Gorge area (Upper Middle Rhine, Nahe, Mosel and Ahr river valleys; Germany). On the background of its long history of cultivation, it is unclear whether S. tectorum is native or naturalized in the Rhine Gorge area. Using S. tectorum from across its geographical range (except SE Europe) as well as S. calcareum, S. minutum and S. marmoreum as three closely related species we conducted a Genotyping-by-Sequencing analysis. The genetic data were used for the identification of genetic groups and for the reconstruction of phylogenetic relationships among these groups. We found that the material from the Rhine Gorge area forms a very homogenous genetic group which is clearly distinct from populations from the Massif Central, Alps and Pyrenees. From this we conclude that S. tectorum is a native of the Rhine Gorge area. The Rhine Gorge material appears to be most closely related to material from the French Massif Central. We hypothesize that the distributional gap between the Rhine Gorge and Massif Central populations is the result of climatic changes in the Quaternary. A wide and continuous distribution area obtained in a Quaternary glacial was disrupted as a result of climatic warming which forced the species into geographically scattered suitable habitats.