Allopatric diversification within Centaurea aplolepa (Asteraceae): insights from population genetics and morphometry

In the context of the Mediterranean region, the plant genus Centaurea (Asteraceae) is one of the most challenging from both taxonomic and systematic perspectives. Despite several contributions that clarified the relationships among taxa within species groups scattered in the region, a knowledge gap still exists for C. aplolepa, a species that shows an impressive taxonomic richness (nine subspecies) in northwestern Italy. To explore the reasons for this high diversity, population genetics with AFLP and morphometric analyses were conducted on 24 populations, comprising all the nine subspecies of the Italian endemic C. aplolepa and additional geographically and phylogenetically close taxa comprising two subspecies of C. leucophaea, C. paniculata, and two species endemic to the island of Elba, C. aetaliae and C. ilvensis. Both population genetics and morphometrics suggest that the high taxonomic diversity in northwestern Italy was overestimated by previous scholars. Nevertheless, both morphological and slight genetic differences allow us to identify some allopatric groups of populations that can be recognized at the infraspecific level. The systematic evidence is translated into a new taxonomic scheme, and a dichotomous key is provided for the identification of taxa as newly circumscribed.