Revision of the high-altitude acidophilous and chionophilous grasslands of the Apennines (Peninsular Italy), a long-lasting intricate syntaxonomic issue

Aims: This paper reports a syntaxonomic and nomenclatural revision of the high-altitude acidophilous and chionophilous grasslands of the Apennines based on a statistical analysis of synoptic tables. Location: The upper montane, subalpine and alpine belts of the whole Apennine range and the Sicily mountains. Methods: The data matrix was composed of 61 frequency columns and 659 taxa. The communities included in the dataset were classified using UPGMA with Chord distance. Indicator Species Analysis, performed for each partitioning level of the dendrogram up to the 20th level, was used to prune the resulting dendrogram. The statistical significance of Indicator Values were tested by a Monte Carlo Test with 5000 permutations. The floristic relationships among syntaxa were visualized by means of Nonmetric Multi-Dimensional Scaling with Chord distance. Results: The distribution area of the alliance Ranunculo-Nardion was restricted to the subalpine belt of the southern Apennines. The acidophilous and sub-acidophilous grasslands of the subalpine and alpine belts of the central Apennines were included in the new alliance Festuco italicae-Nardion strictae, which is composed of two sub-alliances: Festuco italicae-Nardenion strictae and Ranunculo apennini-Trifolienion thalii. The Ranunculo- Nardion and the Festuco italicae-Nardion were classified in the new order Gentianello columnae-Festucetalia italicae, class Juncetea trifidi. The Nardion strictae was restricted to the northern Apennines. The acidophilous grasslands of the lower montane belt of the northern and central Apennines and of the upper part of the southern Apennines were included in the alliance Nardo-Agrostion caninae (Nardetea strictae), which is composed of three suballiances: Nardo-Agrostenion caninae, Campanulo micranthae-Nardenion strictae and Violo pseudogracilis- Bromopsenion erecti. The secondary acidophilous grasslands of the siliceous subtrates of central and southern Calabria were included in the alliance Cirsio vallis-demonis-Nardion, which represents the southernmost limit of the Nardetalia strictae in the Italian Peninsula. The meso-acidophilous communities of the Sicilian mountains (Cirsietalia vallis-demonis) remain an open issue; they were provisionally maintained in the Molinio- Arrhenatheretea. Conclusion: The proposal of the new order Gentianello-Festucetalia fills the gap in the sequence of southern European orders proposed for the acidophilous high-altitude vegetation of the Mediterranean mountains. A solution to the issue of the syntaxonomic classification of the high-altitude Nardus stricta grasslands at the class rank is also proposed. This solution is not exclusively based on the count of the diagnostic species but also on epionthological and syndynamical considerations