Distribution patterns and floristic analysis of the Colymbada tauromenitana (Guss.) Holub populations in Sicily (Italy)

Colymbada tauromenitana (Guss.) Holub (Asteraceae) is a rare paleoendemic, chasmophyte species, occurring on calcareous cliffs in the eastern part of Sicily (Italy). The aim of this work is to analyze the structure and floristic composition of the C. tauromenitana community, in order to characterize the diversity of populations in relation to different ecological data. In all, 61 plots were examined. For each plot, the floristic composition and the cover of the species were determined using the standard relevé method. Three vegetation types emerged from canonical components analysis (CCA), correlated to a gradient of environmental conditions ranging from the coast to inland areas. The first group with Lomelosia cretica and Dianthus rupicola subsp. rupicola was correlated to thermo-xerophilous conditions (lower thermo-Mediterranean belt), the second group with Silene fruticosa and Colymbada tauromenitana was linked to thermophilous conditions (upper thermo-Mediterranean belt) and the third with Dianthus siculus and Odontites bocconei was correlated to mesophilous conditions (meso-Mediterranean belt). Altitude is the main factor influencing both species richness and floristic composition. The density of C. tauromenitana is influenced mainly by rainfall. Finally, we propose a new risk status for this rare species.