An ecological and micromorphological study on the Calabrian (Southern Italy) endemics of the genus Centaurea (Asteraceae)

Calabria is the Italian peninsular region richest in endemic plant species, with Centaurea (Asteraceae) being the most species-rich genus. This study aims to fill key gaps in the integrative taxonomic assessment of seven Calabrian endemics relative to the Apennine-Balkan Centaurea deusta s.str., by providing comparative SEM data on cypselae and pappi and applying explicit niche-overlap tests to these taxa. The highest levels of niche overlap were found among species separated by geographic barriers, while most species selecting similar climatic conditions are allopatric. Overall, the Calabrian endemics occupy suboptimal portions of the C. deusta niche, generally in more thermophilic or more orophilic conditions. Only C. pentadactyli shows a niche that is more divergent from that of C. deusta s.str. than expected by chance. Micromorphological characters of cypselae and pappi proved to be informative and of potential taxonomic relevance. By applying Wettstein's tesseract approach to make the assignment of taxonomic ranks more objective, we conclude that C. aspromontana, C. calabra, C. ionica, C. poeltiana, C. sarfattiana, and C. scillae are best treated at subspecific rank, and the necessary new combinations under C. deusta are here provided. In contrast, based on currently available evidence, C. pentadactyli meets the criteria for retention as a distinct species.