Evolutionary patterns and morphological diversification within the European members of the Euphorbia illirica (E. villosa) group: one or several species?

The Alps and the Carpathians are important centres of plant endemism in Europe, but there are fewer phylogenetic studies on the patterns in biodiversity of Carpathian biota than there are for the Alps. Here, we use nuclear ribosomal ITS, the plastid trnT–trnF region and amplified fragment length polymorphism (AFLP) fingerprinting to determine the phylogenetic position of and relationships within the Euphorbia illirica group and determine the biogeographic links between the Alps and the Carpathians. In addition, we use morphometric data to re-evaluate the controversial taxonomic status of several endemic taxa belonging to this group. ITS and AFLP data indicate that E. austriaca, E. “beskidensis”, E. carpatica, E. semivillosa, E. sojakii and E. illirica (E. villosa) are members of the E. illirica group and E. palustris is their sister, whereas in the plastid dataset E. palustris is nested within the E. illirica group. Additionally, AFLP data indicate a genetic split into two geographical groups, one including Carpathian populations and the other comprising all other populations. The split thus supports the role of the Carpathians as an important Pleistocene refugium, but does not offer support for traditionally recognized taxa within the group. Moreover, the previously suggested biogeographic link between the Alpine E. austriaca and the Carpathian E. sojakii is not supported by molecular data. Instead, it appears likely that the similar morphology of subalpine populations in the E. illirica group developed in parallel in both genetic groups, in E. austriaca in the north-eastern Alps and independently in the Carpathian high altitude taxa. Morphometric analyses show strong overlap both among the taxa and between the two genetic groups, which, in connection with the morphological plasticity of the group, prevents recognition of morphologically identifiable evolutionary units. It thus seems reasonable to treat the members of this group as a single polymorphic species, E. illirica, following the concept proposed in Flora Europaea.