The bryophyte vegetation of gypsum outcrops: a focus on communities with Tortula revolvens

This paper describes a bryosociological study on the gypsicolous bryophyte communities of the Mediterranean area and central Europe, characterized by Tortula revolvens, the only bryophyte that is strictly gypsophytic. The cluster analysis has emphasized the occurrence of four associations belonging to the class Psoretea decipientis, well differentiated as concerns the ecological requirements and floristic composition; they are: Tortuletum revolventis and Trichostomo crispuli-Tortuletum revolventis of the order Barbuletalia unguiculatae, Crossidio crassinervis-Tortuletum obtusatae and Trichostomopso-Tortuletum obutasatae of the order Tortulo brevissimae-Aloinetalia bifrontis. Trichostomo crispuli-Tortuletum revolventis is here described as new. Considering the ecological requirements, type of gypsum outcrop and topographic location, it is possible to identify three distribution models: a first model with distribution in dry areas of central Europe and in Sicily, a second one with core distribution in the driest areas of southern Spain, and a third one in the semidesert and desert areas of Tunisia, Jordan and Israel.