Syntaxonomy of the Parietarietea judaicae class in Europe.

On the basis of literature and unpublished data, a syntaxonomical review about the chasmophilous sinanthropic vegetation occurring in the Mediterranean territories and in the Atlantic and Central Europe was carried out. These plant communities are linked to masonry walls and rocky faces heavily disturbed by men, which are colonized by a fairly specialized flora dominated by hemicriptophytes, chamaephytes and mosses. From the syntaxonomical point of view, in accordance with the greatest part of the authors who studied the matter, the wall vegetation must be considered in a well-distinguished class whose valid name is Parietarietea judaicae Oberd. 1977, rather than in the Asplenietea trichomanis class, as proposed by other authors. Within the class one order, Tortulo-Cymbalarietalia Segal 1969, and three alliances have been recognized: they are Parietarion judaicae Segal 1969, Cymbalario-Asplenion Segal 1969 and Parietario judaicae-Hyoscyamion aurei all. nova. The first of the alliances, chiefly linked to the Mediterranean bioclimate, is charaterized mainly by thermophilous chamaephytes while the cryptogams are almost absent; the second one, distributed in the territories having a temperate bioclimate, is differentiated by an high abundance of ferns and mosses; finally the third one, characterized by a thermo-xerophilous pool of chamaephytes, can be considered a S.-E. Mediterranean vicariant of the Paretarion judaicae alliance. For each syntaxon the nomenclatural type and synonims are reported, as well as the indication of the main ecological, floristic and chorological characteristics.