Gentianella (Gentianaceae): A model taxon for evolution in the Alps

Most taxa of European Gentianella sect. Gentianella are members of the group of Gentianella germanica, which is represented with 11 of its 15 taxa in the Alps. However, due to often minor morphological differentiation many of these taxa are lumped into informal aggregates. We give here an overview on taxonomy, distribution, and regional patterns in groups of closely related taxa and discuss evolutionary scenarios essentially based on morphological and AFLP evidence from earlier studies and new cpDNA RFLP data. Pleistocene climatic oscillations have obviously driven evolution in this group and have favoured cryptic speciation in G. germanica agg. resulting in the two widespread taxa G. germanica and G. rhaetica that may have come in secondary contact after the last glaciation in the western Alps. Other regional and local endemics from G. anisodonta agg. such as G. engadinensis and G. liburnica may represent peripheral isolates of G. anisodonta separated from this taxon by peripatric or parapatric speciation. There is also evidence for complex scenarios of introgression and reticulate evolution among G. rhaetica, G. obtusifolia, and G. austriaca in the eastern Alps. Such reticulate patterns and/or ancient polymorphism towards south-eastern Europe may be the reason for unclear relationships within G. austriaca agg. and its relation to other taxa.