On the taxonomy, origin and diversification of Euphorbia gasparrinii Boiss.

The Mediterranean Basin is one of the richest areas in the world in terms of animal and plant diversity. It is the diversification centre of the Euphorbia verrucosa alliance (Euphorbiaceae), which is distributed from the Balkan to the Iberian Peninsula. Euphorbia gasparrinii is an Italian endemic disjunctly distributed in mountains of the central Apennines and Sicily. In the past it was considered closely related to either the Balkan-Pannonian E. epithymoides or to E. verrucosa. Applying molecular (Amplified Fragment Length Polymorphism fingerprinting, AFLP, and sequencing of nuclear ribosomal ITS), karyological (relative genome size estimations and chromosome counts) and morphometric methods we explored the origin of E. gasparrinii and its diversification from closely related species. Molecular data show that E. gasaparrinii belongs to the E. verrucosa alliance and not to the E. epithymoides group as previosly assumed. Within the E. verrucosa alliance three phylogeographic groups were revealed by AFLP data, corresponding to Balkan-Central European-north Italian E. verrucosa, Italian E. gasparrinii and Iberian E. flavicoma. The genetic differentiation among them is weak, suggesting a Pleistocene divergence and survival in the three southern European peninsulas during Pleistocene glaciations. The morphological variability within the three phylogeographic groups is very high and it is thus difficult to distinguish the members of the groups morphologically. However, karyological analyses revealed that populations of E. gasparrinii have 2n = 16 chromosomes, whereas the other two taxa have 2n = 14. This is, along with weak genetic differentiation and allopatric distribution, a basis for recognizing it as an independent species. In addition, the Iberian populations of E. flavicoma differ in relative genome size from E. gasparrinii and E. verrucosa, but additional studies are needed to disentangle the relationships between E. flavicoma and E. verrucosa. Last but not least, our study – along with the previously published chromosome counts for E. flavicoma – showed multiple autopolyploidisation events within all three taxa, mostly in high-altitude populations. Contrary to the diploid Apennine populations, the only nowadays known Sicilian population of E. gasparrinii is tetraploid. The Sicilian distribution of E. gasparrinii decreased significantly during the past century rendering the species in Sicily critically endangered. This is in line with increasing evidence that Mediterranean high mountain plants are suffering severe range contractions due to climate warming and active measures should be taken to prevent their extinction in the near future