Tage der Biodiversität 2027

The Euphorbia glareosa group constitutes one of the taxonomically most complex lineages within Euphorbia. It comprises several closely related taxa distributed in south-eastern Europe and western Asia, in particular in the Pannonian and Pontic steppes, grasslands of the eastern Balkan Peninsula, across Asia Minor and the Caucasus. The group exhibits remarkable variation in morphology, relative genome size, and partly ploidy level, suggesting a complex evolutionary history. A number of species and infraspecific taxa have been described, yet their delimitations remain ambiguous. Conventional molecular studies founded upon single DNA sequences have failed to provide adequate phylogenetic resolution, thereby impeding elucidation of the taxonomic relationships. The objective of this study was to utilise an integrative taxonomic approach, underpinned by extensive field sampling across the distribution area, to resolve evolutionary relationships and species delimitations within the E. glareosa group. In order to achieve this, we employed a combination of genomic data with morphometric analyses, chromosome counts, and relative genome size measurements. Our data demonstrate that the extrazonal Pannonian populations occurring also in eastern Austria – formerly treated as either E. glareosa, E. nicaeensis or E. pannonica – are most closely related to the populations from the Balkan Peninsula and western Anatolia. The closest relatives of these populations are those from the zonal Pontic steppes, which have traditionally been classified as E. stepposa. In contrast, E. nicaeensis and E. glareosa are phylogenetically more divergent and restricted to the western Mediterranean and Pontic-Caucasian steppes, respectively. The Pannonian populations including those in eastern Austria should thus be named E. pannonica. Given high morphological similarity and genetic admixture between E. pannonica and E. stepposa in the transition area of the steppes of the eastern Balkan Peninsula, the latter should be in the future treated as a subspecies of E. pannonica. The present study underscores the significance of distribution-wide sampling, encompassing type localities and the employment of diverse methodologies, in elucidating the evolutionary history and taxonomic status within taxonomically intricate and morphologically diverse plant groups. It also provides further evidence to support the hypothesis of divergence between the zonal and extrazonal steppes in south-eastern Europe.