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This article presents the results of a study on plant diversity at different levels in residual forest stands, located in the historical Favorita Park in Palermo, Italy (established and named in 1799 by King Ferdinand IV of the House of Bourbon). These forest aspects have naturally evolved for over two centuries, under minimal conditions of anthropogenic disturbance (e.g. deforestation, fires, grazing activities, etc.). This is especially true in the area known as “Bosco Niscemi”, spread over about 8.5 hectares, in the centre of the park. Bosco Niscemi is characterized by the widespread presence of old trees, abundant necromass and litter. In this study, four different soil profiles were analysed, and classified as follows: (i) Solimovic Regosol (Arenic); ii) Eutric Arenosol (Chromic); (iii) and (iv) Skeletic Regosol (Ochric). From a phytosociological point of view, four forest communities have been identified, two of which are described as new associations (Viburno tini-Phillyreetum latifoliae ass. nova and Teucrio flavi-Phillyreetum latifoliae ass. nova). The species richness was also found to be noteworthy, with the co-occurrence of several taxa (phanerogams and cryptogams) that are of biogeographic interest or rare in Sicily, including: i) vascular flora (e.g. Viburnum tinus and Arbutus unedo, both very rare throughout the western sector of Sicily); ii) bryophytes [Cryphaea heteromalla (new record of a very rare species in Sicily) as well as Hypnum cupressiforme and Leptodon smithii, also never previously found at such low altitudes]; iii) lichens (e.g. Bacidia rosella, Gyalecta derivata, Ramalina roesleri and Waynea stoechadiana); iv) mushrooms (e.g. Eichleriella leucophaea, only known location in Italy). Based on the scientific documentation produced in this study, these woods can be reported as “old-growth forests” to be included in the “National Network” that has been recently established in Italy (Ministerial Decree of 23 June 2023). This area might serve as an ideal control for urban environmental studies, given its pristine ecological setting.

This paper illustrates the results of a survey aimed at deepening available knowledge on the ecology of Ptilostemon greuteri (Asteraceae), a very rare palaeoendemic and relict nano-phanerophyte discovered about 15 years ago on Monte Inici, near Castellammare del Golfo (province of Trapani, north-western Sicily). Two plant communities characterised by P. greuteri are described in detail; they occur in the locus classicus and in a second, recently discovered stand, which is also very localised and threatened by fire. The field investigations revealed that the sites where the species grows are very similar from the ecological point of view; in fact, both of them are located on the steep slopes of deep gullies, benefitting from constantly cool and shady microclimatic conditions, and allowed to a) better identify the currently preferred habitat (ledges, screes at the base of cliffs), b) analyse from a floristic and phytosociological point of view the maquis communities where P. greuteri grows as co-dominant or dominant species, referable to the class Quercetea ilicis, c) to identify the syndynamic role that these coenoses play within the series and microgeoseries of local vegetation. As far as syntaxonomy is concerned, the Malvo olbiae-Ptilostemonetum greuteri ass. nova is described, a basiphilous, thermophilous and shade-tolerant maquis framed in the Oleo-Ceratonion alliance. Moreover, two subassociations are described: 1) typicum subass. nova, corresponding to a pioneer maquis community prevailing on the coarse, loose and mobile debris located along the slopes at the base of rock cliffs, where P. greuteri is clearly dominant and shows a nano-phanerophytic habitus, and 2) euphorbietosum bivonae subass. nova, a primary aspect found of the ledges of carbonate cliffs, where the species can play either a dominant or co-dominant role with other elements of the maquis (Euphorbia bivonae, Chamaerops humilis, etc.), sometimes showing a slightly smaller size.

Field investigation carried out by the Sicilian botanists in the last 20 years enabled them to identify eight habitat types of high biogeographic and conservation interest, neglected by the Directive 92/43, which deserve ad hoc conservation measures. For each of these habitats, a syntaxonomic interpretation of the corresponding plant communities, their main ecological, physiognomic and syndynamic traits and a list of diagnostic species are provided. Their classification into the macrotypes listed in the Annex I of the Directive 92/43 and the respective correspondence in EUNIS habitat classification are proposed. The habitats here described integrate those already proposed by the Italian Botanical Society, with the hope of an adequate recognition at national at supranational level.

The freshwater aquatic vegetation of the Lemnetea and Potamogetonetea classes in Western Sicily was surveyed and analyzed. 85 lakes and small pools were investigated collecting 147 phytosociological unpublished relevés to integrate the very scarce available data (only 3 relevés). By applying statistical analyses on abundances data and on the bases of physiognomy and dominant species, two alliances (Lemnion minoris and Stratiotion) and four different coenoses have been identify for the Lemnetea class; while 11 associations, assigned to two orders (Potamogetonetalia pectinati and Callitricho hamulatae-Ranunculetalia aquatilis) and four alliances (Potamogetonion, Nymphaeion albae, Ranunculion aquatilis and Ranunculion omiophyllo-hederacei) have been recognized for the Potamogetonetea class. A new association (Junco bufonii-Ranunculetum omiophylli ass. nov.) and a new subassociation (Ranunculetum peltati ranunculetosum rionii subass. nov.) have been proposed, whereas other six vegetation units were found to be new for the study area (Potamogetono-Ceratophylletum submersi, Potamogetonetum pusilli, Ranunculetum aquatilis, Ranunculetum peltati and Ranunculetum rionii, Lemno-Callitrichetum obtusangulae). For all the coenoses recognized, new insights on the floristic composition, syntaxonomy, synphiognomy, synecology and synchorology are reported, offering a reasoned overview of the aquatic vegetation of the western sector of the main Mediterranean island.