Alnus glutinosa Riparian Woodlands of Italy and Corsica: Phytosociological Classification and Floristic Diversity

Abstract

A comparative analysis of the riparian vegetation dominated by Alnus glutinosa in Italy and Tyrrhenian islands, based on literature data and unpublished relevés, is presented. A total of 456 phytosociological relevés were processed. For the definition of plant communities and alliances, hierarchical clustering was performed by using Bray-Curtis coefficient and Detrended Correspondence Analysis ordination methods. Identification of diagnostic species of the vegetation units was performed by means of the phi fidelity index. Quantum GIS software version 3.6 was used for the interpolation of the bioclimatic variables and A. glutinosa communities. Overall, a total of 18 A. glutinosa-riparian wood communities were distinguished for Italy and Tyrrhenian islands, of which two new associations and one new subassassociation are described. The classification of the relevés showed two main vegetation groups: the first one including the plant communities of the Osmundo-Alnion alliance, and the other including the vegetation of the Ligustro vulgaris-Alnion glutinosae alliance. This latest includes the riparian meso-thermophilous communities of central and northern Italy. Within the Osmundo-Alnion alliance, two subgroups can be recognized: the first one includes the thermophilous communities of the Hyperico hircini-Alnenion glutinosae sub-alliance, mainly spread in the Tyrrhenian islands, while the second group includes the mesophilous communities attributed to the new suballiance Struthioptero-Alnenion glutinosae, widespread in central Italy and the Corsican mountains. The present paper provides the first comprehensive and exhaustive scheme of the A. glutinosa riparian woodlands diversity in Italy and Corsica.

1. Introduction

Riparian woods and forests represent transitional habitats strongly dependent on hydrology and fluvial processes. These riparian ecosystems constitute a very important resource in the context of ecosystem services, such as protection from erosion, flow regulation, ecological corridors and effective control for non-point source pollution [1,2,3]. In a perspective of environmental sustainability, it is necessary to guarantee their presence, permanence, quality and restoration. The ecological importance of riparian habitats regarding their structure, functionality and biodiversity conservation has been recognised in the Habitat Directive of the European Union [4]. In particular, Alnus glutinosa communities are recognized as priority habitat Code 91E0* “Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae)”. Unfortunately, in the Mediterranean Basin all riparian habitats are under severe human pressures, such as modification of the riparian areas determined by the artificialization and cleaning of the riverbeds, water catchment for irrigation and industrial uses, construction of dams or other barriers with consequent submersion upstream and flow reduction downstream and, last but not least, by agro-pastoral activities [5,6], which often cause the alteration of the structure and floristic composition of these plant communities and a consequent loss of ecosystem services [7]. As regards Italy, the fourth national reporting of the Habitats Directive (2013–2018; www.reportingdirettivahabitat.it (accessed on 12 October 2022)) stated high vulnerability for riparian forest habitats such as 92A0 (Salix alba and Populus alba galleries) and the above-mentioned 91E0*, with a poor state of conservation worsening compared to the previous reporting (2007–2012), in both the Mediterranean and continental bioregions.

In order to support the sustainable management of riparian habitats, their vegetation must first be carefully delineated in terms of structural features and floristic composition [8]. From the viewpoint of vegetation science, European temperate floodplain forests and zonal deciduous forests have been traditionally included either in the Querco-Fagetea class [9,10] or the Carpino-Fagetea class [11]. Recently, a last arrangement has been proposed by Mucina et al. [12], including the riparian forests of the Eurosiberian and Mediterranean regions in the class Alno glutinosae-Populetea albae P. Fukarek et Fabijanić 1968, and separating this class into two orders: Alno-Fraxinetalia, which includes the floodplain riparian forests of temperate and boreal Europe, and Populetalia albae, which groups the Mediterranean and submediterranean riparian forests. In fact, the separation in two orders had been previously proposed by Passarge [13], Dierschke [9], and more recently reiterated by Biurrun et al. [14].

According to Biondi et al. [15,16], the Italian riparian woods are mainly included in the Salici purpureae-Populetea nigrae class and in the Populetalia albae order, which comprises several alliances: Populion albae, Alno-Quercion roboris, Osmundo regalis-Alnion glutinosae, Alnion incanae, Platanion orientalis, Carici remotae-Fraxinion oxycarpae, Ligustro vulgaris-Alnion glutinosae. Within this class, the riparian forests dominated by A. glutinosa, subject of our study, are generally included in the Osmundo-Alnion or Ligustro vulgaris-Alnion glutinosae alliance. The Osmundo-Alnion (Br.-Bl. et al. 1956) Dierschke et Rivas-Martínez in Rivas-Martínez 1975 includes the oceanic vegetation dominated by A. glutinosa and Fraxinus angustifolia, mainly distributed in the Iberian Peninsula and composed by species with Atlantic distribution and Iberian endemisms [17]; it is divided into two sub-alliances: Osmundo-Alnenion, with Iberian distribution [18], and Hyperico hircine-Alnenion glutinosae, with Tyrrhenian distribution [19,20]. The Ligustro vulgaris-Alnion glutinosae includes riparian Alnus glutinosa-rich communities of the lowland-hilly belt of northern Italy to the montane one of central-southern Italy [16].

A. glutinosa communities are also interesting from a phytogeographical point of view, considering that this paleotemperate species found refuge in the Mediterranean area during the Quaternary coldest periods. It is likely that many populations have remained permanently isolated in the Mediterranean since the last glacial maximum [21,22], and therefore the postglacial repopulation of Europe would have taken place from refugia located further North of the area under investigation.

The aim of this study is to provide an overview of the riparian wood communities dominated by A. glutinosa in Italy and Corsica, along with a review of all syntaxa described so far, in order to provide a coherent phytosociological synthesis taking into account floristic, chorologic, and ecological features.

2. Materials and Methods

2.1. Phytosociological Data

The study followed the Braun–Blanquet phytosociological approach [23,24] according to fundamental and updated concepts recommended by Dengler et al. [25,26], Biondi [27], and Pott [28]. The sparse communities with A. glutinosa coverage values less than 20% (+1, 2) have not been taken into consideration for processing. A total of 456 phytosociological relevés per 310 species were processed, of which 377 from the literature and 79 unpublished. Original Braun–Blanquet sampling scale was transformed into the ordinal scale according to Van der Maarel [29]. All the relevés were analyzed using classification and ordination methods.

2.2. Statistical Analysis

A multivariate analysis (Linkage method: Ward’s, Distance measure: Bray–Curtis) was applied [30,31]. The optimal number of clusters was identified using the Silhouette index by means of the cluster package in R software [32]. Cluster analysis and ordination of the dataset were performed using PC-ORD 6 software [33]. Ordination (DCA) took into account the bioclimatic variables at 30 s resolution from WorldClim [34]. Quantum GIS software version 3.6 was used for the interpolation of the bioclimatic variables and A. glutinosa communities. Diagnostic species of the vegetation units (partitions) was performed by software JUICE [35]. It was determined by means of their fidelity (phi coefficient), and each group was standardized in order to remove dependence of the phi coefficient on unequal sizes; non-significant phi values at p > 0.05 were excluded based on Fisher’s exact test [36]; species with phi > 0.3 were considered as diagnostic and species with phi > 0.4 as highly diagnostic. Then, the syntaxonomic identification of the obtained partitions was carried out on the basis of diagnostic species, author’s own expert knowledge and the literature. For the class description, the list of characteristic species from the literature was reported; for orders and alliances, both the list of statistical species (according to JUICE) and the list of the traditional species from the literature; for associations, the complete lists of diagnostics, constant and dominant species were reported, along with the characteristic species reported by the authors of each association. It is worth noting that in the list of the faithful species are included many species belonging to other syntaxa, such as Querco-Fagetea, Quercetea ilicis or Artemisietea vulgaris; as a result, the real number of true diagnostic species is much lower than the one resulting from the analysis.

2.3. Plant Communities Processed

The processed relevés from the literature were classified into the following syntaxa: Oenantho crocatae-Alnetum glutinosae, Glechomo-Alnetum glutinosae, Osmundo-Alnetum glutinosae for Sardinia [20,37,38,39], Circaeo lutetianae-Alnetum glutinosae, Polysticho-Alnetum glutinosae, Hyperico hircini-Alnetum glutinosae, Aro italici-Alnetum glutinosae for Latium [40,41,42,43,44], Carici microcarpae-Alnetum glutinosae, Carici pallescentis-Alnetum glutinosae, Circaeo lutetianae-Alnetum glutinosae, Aro italici-Alnetum glutinosae, Alno glutinosae-Fraxinetum oxycarpae for Tuscany [45,46,47,48,49,50,51,52,53], Aro italici-Alnetum glutinosae, Aro italici-Alnetum glutinosae, Alno-Fraxinetum oxycarpae for Marche [54,55,56], Alno-Fraxinetum oxycarpae for Emilia Romagna [57], Euphorbio corallioides-Alnetum glutinosae for Campania [58], Hyperico hircini-Alnetum glutinosae, Angelico sylvestris-Alnetum glutinosae, Polysticho-Alnetum glutinosae, Euphorbio corallioides-Alnetum glutinosae for Calabria [55,59,60,61], Platano-Salicetum gussonei alnetosum, Alnus glutinosa communities for Sicily [62], Eupatorio corsici-Alnetum glutinosae, Scrophulario auriculatae-Alnetum glutinosae, Scolopendrio officinalis-Alnetum glutinosae, Athyrio filicis-feminae-Gentianetum asclepiadeae for Corsica [19,63,64,65], Lamio orvalae-Alnetum glutinosae for Friuli Venezia Giulia, Veneto, Lombardy [66], Aro italici-Alnetum glutinosae, Alnus glutinosa community for Umbria [67,68,69,70], Aro italici-Alnetum glutinosae for Abruzzo [71,72].

2.4. Taxonomic, Syntaxonomic Nomenclature and Bioclimatic Classification

Taxonomic nomenclature for native species follows Bartolucci et al. [73], and Pignatti [74,75,76,77], while for non-native species follows Galasso et al. [78]. Syntaxonomic classification follows Mucina et al. [12]. The bioclimatic classification follows Pesaresi et al. [79]. The names of syntaxa comply with the International Code of Phytosociological Nomenclature (ICPN) [80].

3. Results and Discussions

Classification of the relevés (cophenetic correlation = 0.577) showed two main vegetation groups (Figure 1 and Figure 2): the first one (cluster A) including the plant communities of the Osmundo-Alnion alliance, with an Ibero-Atlantic-Mediterranean distribution, growing in the presence of oligotrophic water and watercourses that do not dry up in summer, in contact with the water table or near springs; the second one (cluster B) including the vegetation of the Ligustro vulgaris-Alnion glutinosae alliance, occuring from the lowland-hilly belt of northern Italy to the montane one of central-southern Italy. Within the Osmundo-Alnion alliance, two subgroups can be distinguished: the first one includes the thermophilous communities of the Hyperico hircini-Alnenion glutinosae sub-alliance, mainly spread in the Tyrrhenian islands (Corsica, Sardinia, Sicily, Elba Island), while the second group includes the mesophilous communities, well differentiated from a floristic and ecological point of view from the Hyperico hircini-Alnenion glutinosae, for which a new sub-alliance called Struthioptero-Alnenion glutinosae, widespread in central Italy and the Corsican mountains, is here proposed.

The DCA (Figure 3) shows a clear split into three groups. In particular, on the positive side of axis 2 there are the plant communities included in the Hyperico hircini-Alnenion glutinosae sub-alliance linked to thermophilous environmental conditions (BIO 4,7,14,17,18), while on the negative side of axis 1 are distributed the communities belonging to Ligustro vulgaris-Alnion glutinosae linked to meso-thermophilous climatic conditions (BIO 1,5,6, 8,10,11,15). On the negative side of axis 2, we find the communities included in Struthioptero-Alnenion glutinosae, linked to the mesophilous environment’s conditions.

Regarding the distribution of the syntaxa showed in Figure 1, it could be interesting to make a comparison with the geographical distribution of the haplotypes known in the literature for A. glutinosa [81,82], which indicates how the Calabrian and Corsican populations are isolated and both show affinity with those of North Africa (East Algeria and North Tunisia) [83]. These affinities seem to reflect the paleogoegraphic history of these territories [83,84,85], which is also reflected in the floristic cortege and the consequent syntaxonomic framework, that is the Hyperico-Alnenion suballiance grouping plant communities of Corsica, Sardinia and Sicily. On the contrary, the Calabrian populations isolated from those of northern Italy show a floristic cortege close to northern Italian and European territories, as shown by their inclusion, for the most part, within Ligustro vulgaris-Alnion glutinosae alliance. The synoptic table (Table S1) reveals the differences in floristic composition between the forest types, and their alliances/suballiances, identified on the basis of diagnostic species (i.e., in light grey, the diagnostic and, in dark grey, the highly diagnostic species). A total of 18 plant communities were identified based on silhouette width (Figure 4). The complete syntaxonomical scheme and the description of these plant communities are provided below.

3.1. Syntaxonomical Scheme

Alno glutinosae-Populetea albae P. Fukarek et Fabijanić 1968

Populetalia albae Br.-Bl. ex Tchou 1948

A. Osmundo regalis-Alnion glutinosae (Br.-Bl. et al. 1956) Dierschke and Rivas-Martínez in Rivas-Martínez 1975

A1. Hyperico hircini-Alnenion glutinosae Dierschke 1975

1-Osmundo-Alnetum glutinosae Van den Berghen 1971

2-Oenantho crocatae-Alnetum glutinosae Arrigoni et al. 1996

3-Platano orientalis-Alnetum glutinosae (Brullo et Spampinato 1990) Sciandrello et al. nom. nov. hoc loco

4-Eupatorio corsici-Alnetum glutinosae Dierschke 1975

4. a. typicum

4. b. scolopendrietosum nom. nov. hoc loco

A2. Struthioptero-Alnenion glutinosae_suball. nov. hoc loco

5-Glechomo sardoae-Alnetum glutinosae Arrigoni 1986

6-Gentiano asclepiadeae-Alnetum glutinosae (Litard. and Malcuit 1926) Gamisans 1977 corr. Renaux et al. 2019

7-Carici pallescentis-Alnetum glutinosae Landi and Angiolini 2010

8-Carpino betuli-Alnetum glutinosae (Di Pietro et al. 2010) Sciandrello et al. nom. nov. hoc loco

B. Ligustro vulgaris-Alnion glutinosae Poldini, Sburlino and Venanzoni 2015 in Biondi et al. 2015

9-Aro italici-Alnetum glutinosae Gafta and Pedrotti 1996

10-Aegopodio podagariae-Alnetum glutinosae (Blasi and Frondoni 1996) Sciandrello et al. nom. nov. hoc loco

11-Geranio nodosi-Alnetum glutinosae ass. nov. hoc loco subass. typicum

12-Geranio nodosi-Alnetum glutinosae cornetosum sanguineae subass. nov.

13-Hyperico hircini-Alnetum glutinosae Gafta and Pedrotti 1996

14-Lamio orvalae-Alnetum glutinosae Dakskobler 2016

15-Polysticho setiferi-Alnetum glutinosae Brullo, Scelsi, Spampinato 2001

16-Euphorbio corallioides-Alnetum glutinosae Brullo and Furnari in Barbagallo et al. 1982

17-Asperulo taurinae-Alnetum glutinosae ass. nov. hoc loco

18-Angelico sylvestris-Alnetum glutinosae Brullo and Spampinato 1997

3.2. Description of the Vegetation

Alno glutinosae-Populetea albae P. Fukarek et Fabijanić 1968

Riparian woods and forests of the Eurosiberian and Mediterranean biogeographic regions

Characteristic species: Alnus glutinosa, Brachypodium sylvaticum, Elymus caninus, Equisetum hyemale, Equisetum telmateia, Frangula alnus subsp. alnus, Humulus lupulus, Populus nigra, Saponaria officinalis, Solanum dulcamara, Vitis vinifera subsp. sylvestris [12,86].

Populetalia albae Br.-Bl. ex Tchou 1948

Mediterranean floodplain forests

Characteristic species: Aristolochia paucinervis, A. rotunda, Arum alpinum, Carex grioletii, Circaea lutetiana, Fraxinus oxycarpa, Hesperis matronalis subsp. candida, Lamium flexuosum, Lathraea clandestina, Listera ovata, Malus sylvestris, Osmunda regalis, Polystichum setiferum, Populus alba, Pyrus pyraster, Ficaria verna, Salix atrocinerea, Stegnogramma pozoi, Symphytum tuberosum, Ulmus minor, Vinca difformis [86].

A. Osmundo regalis-Alnion glutinosae (Br.-Bl. et al. 1956) Dierschke and Rivas-Martínez in Rivas-Martínez 1975 (Cluster A)

Alder, ash, white poplar and willow formations from soft water rivers and streams, mainly composed of species with Atlantic distribution and Tyrrhenian endemics

Holotypus: Scrophulario-Alnetum glutinosae Br.-Bl. et al. 1956

Diagnostic species: Osmunda regalis, Carex microcarpa, Hypericum hircinum, Asplenium onopteris, Athyrium filix-femina, Cyclamen repandum subsp. repandum, Eupatorium cannabinum subsp. corsicum, Fraxinus ornus, Ilex aquifolium, Oenanthe crocata, Pteridium aquilinum subsp. aquilinum, Smilax aspera.

Characteristic species (according to the literature): Arisarum proboscideum, Brachypodium sylvaticum, Campanula primulifolia, Clematis viticella, Frangula alnus subsp. baetica, Holcus grandiflorus, Scrophularia laevigata, S. scorodonia [86]; Carex elata subsp. reuteriana, Galium broterianum, Oenanthe crocata, Paradisea lusitanica [14].

A1. suball. Hyperico hircini-Alnenion glutinosae Dierschke 1975 (Cluster A1)

Alder woods of the Circumtyrrhenian area (Sardinia, Corsica, north-eastern Sicily, Tyrrhenian coasts of the Italian peninsula)

Holotypus: Eupatorio corsici-Alnetum glutinosae (Litard. 1928) Dierschke 1975

Diagnostic species: Hypericum hircinum, Eupatorium cannabinum subsp. corsicum, Oenanthe crocata, Smilax aspera, Ficus carica, Mentha aquatica, Mentha suaveolens subsp. insularis, Nerium oleander, Phillyrea latifolia, Salix atrocinerea subsp. atrocinerea, Allium triquetrum, Buxus sempervirens, Euphorbia characias, Platanus orientalis, Rubus ulmifolius, Vitis vinifera.

Characteristic species (according to the literature): Hypericum hircinum, Carex microcarpa, Fraxinus ornus, Ficus carica [19].

• 1.Osmundo-Alnetum glutinosae Van den Berghen 1971 (Cluster 1, Figure 5)

Syn.: Eupatorio corsici-Alnetum glutinosae (Litard. 1928) Dierschke 1975 pro parte; Osmundo-Alnetum (Camarda et al. 1995); Salici arrigonii-Alnetum glutinosae (Brullo 1993) Angius and Bacch. 2009

Holotypus: not designated (see synoptic Tab. 3, colum III [87])

Diagnostic species: Eupatorium cannabinum subsp. corsicum, Carex microcarpa, Cyperus badius, Mentha suaveolens subsp. insularis, Oenanthe crocata, Phillyrea latifolia, Salix arrigonii, Salix atrocinerea subsp. atrocinerea, Smilax aspera, Clematis cirrhosa, Euphorbia meuselii, Hypericum hircinum, Nerium oleander, Rhamnus alaternus subsp. alaternus, Carex divulsa, Vitis vinifera.

Constant species: Alnus glutinosa, Brachypodium sylvaticum, Clematis vitalba, Dioscorea communis, Ficus carica, Hedera helix, Hypericum hircinum, Pteridium aquilinum, Rubus ulmifolius.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Hypericum hircinum, Carex microcarpa, Euphorbia meuselii.

Structure and ecology: Edapho-hygrophilous mesowoods (10–20 m high) widespread along oligotrophic rivers and streams, from the sea level up to 800 m of elevation. It is a calcifuge formation, linked to moist sandy to gravelly soils, in the Mediterranean oceanic pluviseasonal bioclimate, with thermotype ranging from the thermomediterranean to the mesomediterranean and ombrotypes between the lower subhumid and the lower humid. Floristically, the tree layer is characterized by the dominance of A. glutinosa with low cover values of Salix atrocinerea subsp. atrocinerea and/or, in the south-westernside of Sardinia, of the endemic Salix arrigonii. The shrubby layer is mainly represented by Hypericum hircinum subsp. hircinum, Erica terminalis, Eupatorium cannabinum subsp. corsicum and Euphorbia meuselii, while the herbaceous layer is characterized by several hygrophilous Tyrrhenian endemic plants, such as Carex microcarpa, Mentha suaveolens subsp. insularis, and Bellium bellidioides.

Distribution: With the exception of the Gennargentu massif and the Marghine-Goceano chain, it is common on all the siliceous substrata of Sardinia. It is especially representative of the riparian formations of the Gallurese (NE Sardinia) and the Sulcitano-Iglesiente (SW Sardinia) biogeographical sectors [20].

Landscape context: It is part of the calcifuge and oligotrophic Sardinian geosigmetum of the thermomediterranean and mesomediterranean bioclimatic belts [88]. It is in contact with the climatophilous holm-oak and edaphophilous cork-oak woods of the Quercetalia ilicis.

Notes: These riparian woods are characterized by a high percentage of Cyrno-Sardinian endemics. In southern Sardinia, the presence of different taxa belonging to the genus Salix enabled to distinguish two subassociations: salicetosum atrocinereae and salicetosum arrigonii [20].

Figure 5. Plant communities and diagnostic species of the Alnus glutinosa riparian woodlands (1) in Sardinia: (2) Hypericum hircinum, characteristic species of the suball. Hyperico hircini-Alnenion glutinosae; (3,4) Osmundo-Alnetum glutinosae (Rio Leni, Iglesiente—Sardinia); (5) Glechomo sardoae-Alnetum glutinosae (Rio Correboi, in the Gennargentu Mounts—Sardinia); (6) Aquilegia nugorensis, plant species of the Glechomo sardoae-Alnetum glutinosae; (7,8) Glechomo sardoae-Alnetum glutinosae (Gennargentu Mounts—Sardinia). Photo credits: O. Caldarella (1,2), L. Gianguzzi (5), G. Bacchetta (3,4,6–8).

Figure 5. Plant communities and diagnostic species of the Alnus glutinosa riparian woodlands (1) in Sardinia: (2) Hypericum hircinum, characteristic species of the suball. Hyperico hircini-Alnenion glutinosae; (3,4) Osmundo-Alnetum glutinosae (Rio Leni, Iglesiente—Sardinia); (5) Glechomo sardoae-Alnetum glutinosae (Rio Correboi, in the Gennargentu Mounts—Sardinia); (6) Aquilegia nugorensis, plant species of the Glechomo sardoae-Alnetum glutinosae; (7,8) Glechomo sardoae-Alnetum glutinosae (Gennargentu Mounts—Sardinia). Photo credits: O. Caldarella (1,2), L. Gianguzzi (5), G. Bacchetta (3,4,6–8).

• 2. Oenantho crocatae-Alnetum glutinosae Arrigoni et al. 1996 (Cluster 2)

Holotypus: Rel. 58, Tab. 4 [38].

Diagnostic species: Adiantum capillus-veneris, Allium subhirsutum, Allium triquetrum, Bellium bellidioides, Bromus sterilis, Catapodium rigidum, Cynosurus effusus (C. glacilis, C. elegans), Dittrichia viscosa, Euphorbia semiperfoliata, Helleborus lividus subsp. corsicus, Hordeum murinum, Leucojum aestivum, Mentha aquatica, Mentha suaveolens subsp. insularis, Nerium oleander, Oenanthe crocata, Parietaria judaica, Phillyrea latifolia, Salix atrocinerea subsp. atrocinerea, Torilis africana, Clematis cirrhosa, Cyclamen repandum subsp. repandum, Geranium purpureum, Smilax aspera.

Constant species: Alnus glutinosa, Brachypodium sylvaticum, Clematis vitalba, Fraxinus ornus, Hedera helix, Rubus ulmifolius.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Oenanthe crocata, Euphorbia semiperfoliata Mentha suaveolens subsp. insularis, Helleborus lividus subsp. corsicus.

Structure and ecology: Edapho-hygrophilous mesowoods (10–20 m high) present along on bedrock temporary rivers and streams submitted to high drought, from the sea level up to 200 m of elevation. It is linked to moist sandy to gravelly soils in the mediterranean oceanic pluviseasonal bioclimate with a thermomediterranean thermotype and ombrotypes between the lower dry and the lower subhumid. Floristically, the tree layer is characterized by the dominance of A. glutinosa with low cover values of Nerium oleander, Salix atrocinerea subsp. atrocinerea and Vitex agnus-castus. The shrubby layer is mainly represented by Hypericum hircinum subsp. hircinum, and Euphorbia semiperfoliata, while in the herbaceous layer there is a rich compendium of thermo-hygrophilous plants, such as Oenanthe crocata, Parietaria judaica, Hordeum murinum and Torilis africana.

Distribution: At the state of the art, it has been described only for the siliceous outcrops of “Sa Pruna” in territory of Dorgali (CE Sardinia). However, it cannot be excluded that some of the uninvestigated alder formations, especially along the eastern coastal strip of Sardinia (from the South of Sarrabus to the North of Gallura), can be included in this association.

Landscape context: It belongs to the calcifuge and oligotrophic Sardinian geosigmetum of the thermomediterranean bioclimatic belt, which includes the vegetation succession, from the coastal associations of the Nerio-tamaricetea to less thermophylous formations of the Alno glutinosae-Populetea albae [88]. It is often in contact with the climatophilous holm-oak woods of the Quercetalia ilicis.

Notes: Even though this work confirms the differentiation of this communities from the more widespread Osmundo-Alnetum glutinosae association, further investigations are needed to better define their distribution and ecological delimitations.

• 3. Platano orientalis-Alnetum glutinosae (Brullo et Spampinato 1990) Sciandrello et al. nom. nov. hoc loco (Cluster 3, Figure 6)

Syn.: Platano-Salicetum gussonei Brullo et Spampinato 1990 subass. alnetosum glutinosae Brullo et Spampinato 1990

Holotypus: Rel. 14, Tab. 3 [62].

Diagnostic species: Agrostis castellana, Anthriscus nemorosa, Clinopodium arundanum, Euphorbia characias, Holcus lanatus subsp. lanatus, Mentha suaveolens, Platanus orientalis, Salix gussonei, Asparagus acutifolius, Epilobium parviflorus, Eupatorium cannabinum, Hypericum hircinum, Lamium flexuosum, Tussilago farfara.

Constant species: Alnus glutinosa, Brachypodium sylvaticum, Carex pendula, Clematis vitalba, Hedera helix subsp. helix, Mycelis muralis, Polystichum setiferum, Rubus ulmifolius, Viola alba subsp. dehnhardtii.

Dominant species: Alnus glutinosa.

Characteristic species: Salix gussonei

Structure and ecology: This riparian wood grows on siliceous substrata (phyllites, gneiss, vulcanite) along the rivers of more or less recessed deep valleys, scattered in the mountain belt at 400–800 m of altitude or in correspondence of the intermediate stretches of rivers (“fiumare”). It is circumscribed to the riparian environments, featured by a very humid and fresh micro-climate, linked to thermomediterranean and mesomediterranean bioclimatic belts. Floristically, the tree layer is characterized by the dominance of Alnus glutionsa with low cover values of Platanus orientalis, the shrubby layer from Hypericum hircinum subsp. majus, Sambucus nigra, Nerium oleander and Ficus carica, while the herbaceous layer is characterized by a pool of hygrophilous-calcifuge ferns, such as Polystichum setiferum, Dryopteris affinis, Anthyrium filix-femina, Osmunda regalis, as well as Brachypodium sylvaticum, Carex pendula, Viola alba subsp. dehnhardtii, Lamium flexuosum, Agrostis castellana, etc. Furthermore, the cenosis is enriched with some lianas, such as Clematis vitalba, Hedera helix, Rubus ulmifolius, Asparagus acutifolius, and Dioscorea communis (

Table 1. Platano orientalis-Alnetum glutinosae (Brullo et Spampinato 1990) Sciandrello et al. nom. nov. hoc loco. Appendix A.

Rel. Numbers	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25
Rel. Numbers Cluster	219	220	221	222	223	226	227	228	229	230	231	232	233	234	235	236	237	238	239	240	241	242	243	244	245
Rel. Numbers from the literature	12	13	16	14 *	15	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-
Area (m2)	50	100	100	100	100	100	100	100	150	150	150	150	100	100	150	100	100	100	100	100	100	100	100	100	100
Aspect	-	-	-	-	-	-	-	-	NE	NW	SE	SE	SE	E	E	E	E	SE	SE	NE	NE	SE	E	E	E
Slope (°)	-	-	-	-	-	-	-	-	8	5	10	10	10	10	5	5	5	5	5	5	5	5	5	5	5
Tree cover (%)	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100
Shrum cover (%)	-	-	-	-	-	20	40	20	60	50	50	60	60	50	50	60	50	70	60	40	60	50	80	70	80
Herbaceous cover (%)	-	-	-	-	-	-	-	-	40	30	40	40	40	40	50	50	50	30	40	60	40	50	30	40	30
Altitude (m s.l.m.)	380	400	420	450	490	465	466	467	270	285	430	470	490	400	280	442	455	460	458	600	600	576	575	572	570
Richness floristic	7	18	12	11	12	11	20	19	28	20	17	26	23	25	29	27	28	27	29	27	29	30	27	24	27
Char. Ass.
Platanus orientalis	2	2	2	2	1	1	2	3	1	1	1	1	2	.	1	1	2	1	+	1	2	+	1	2	1
Char. Alno glutinosae-Populetea albae and Populetalia albae
Alnus glutinosa	5	4	5	4	5	5	4	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5
Polystichum setiferum	.	.	.	.	.	.	.	.	.	.	+	1	+	1	1	1	+	+	+	2	1	1	1	1	1
Brachypodium sylvaticum subsp. sylvaticum	2	3	3	.	1	.	.	.	2	1	2	2	2	2	3	2	3	2	1	2	1	1	+	+	1
Carex pendula	.	.	+	.	.	.	.	.	1	1	.	1	+	.	1	+	+	1	+	+	+	+	1	+	+
Sambucus nigra	.	.	.	.	.	.	.	.	1	1	.	1	2	1	1	2	1	1	+	+	+	.	.	.	.
Populus nigra	.	1	1	+	.	1	2	1	.	.	.	.	.	2	.	.	.	.	.	.	.	.	.	.	.
Salix alba	.	.	.	.	.	.	1	.	1	1	.	.	.	1	2	.	.	.	.	.	.	.	.	.	.
Ulmus minor	.	.	.	.	.	.	.	.	.	.	.	1	.	1	.	1	1	.	1	.	.	.	.	.	.
Carex remota	.	.	.	.	.	+	+	1	.	+	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.
Salix gussonei	1	+	2	3	2	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Equisetum telmateia	.	.	.	.	.	.	.	.	.	.	1	.	.	1	1	.	.	.	.	.	.	.	.	.	.
Char. Osmundo regalis-Alnion glutinosae
Athyrium filix-femina	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	+	+	.	.	1	.	+	.	.	.
Osmunda regalis	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Char. Hyperico hircini–Alnenion glutinosae
Hypericum hircinum	.	+	2	.	+	.	.	.	+	1	2	2	1	1	1	2	1	3	1	1	2	2	1	1	2
Lamium flexuosum	.	.	.	.	.	1	1	1	1	1	.	+	1	+	.	2	1	+	+	1	+	+	+	1	+
Fraxinus ornus	.	.	.	.	.	.	.	.	.	.	.	1	1	1	1	+	.	.	.	.	+	1	1	1	1
Ficus carica	.	.	.	.	.	.	.	.	.	.	.	.	1	1	1	1	1	2	1	.	1	+	.	.	1
Other species
Rubus ulmifolius	.	2	.	+	1	1	2	1	2	1	2	2	2	1	1	2	2	1	2	1	3	2	2	2	3
Hedera helix subsp. helix	.	.	.	.	+	1	+	+	1	1	1	1	2	+	2	1	1	1	2	1	1	2	2	3	2
Eupatorium cannabinum	2	1	.	1	.	.	.	.	+	+	2	1	2	1	1	2	2	2	1	1	1	1	1	+	+
Clematis vitalba	.	.	+	.	.	+	+	.	+	1	.	1	1	.	1	1	2	1	1	2	1	2	1	1	+
Euphorbia characias	.	.	.	+	+	.	+	+	.	.	1	1	1	+	+	+	1	+	+	+	+	.	.	+	+
Mentha suaveolens	.	.	.	.	.	.	.	.	1	+	2	1	1	+	1	.	+	+	+	1	+	+	+	+	+
Holcus lanatus subsp. lanatus	.	.	.	.	.	.	.	.	1	+	.	.	+	+	+	+	+	1	1	1	+	1	1	+	+
Mycelis muralis	.	.	.	.	.	.	+	+	.	+	.	.	.	.	.	+	1	+	1	1	1	+	+	+	+
Viola alba subsp. dehnhardtii	.	.	.	+	+	.	+	+	1	.	+	.	.	.	+	.	.	.	.	1	1	1	+	1	+
Dioscorea communis	.	+	.	.	.	.	.	.	.	.	.	.	.	.	1	1	1	1	1	+	.	+	+	+	+
Pteridium aquilinum subsp. aquilinum	.	.	.	.	.	.	.	.	.	.	+	+	.	1	+	+	1	+	+	1	1	+	.	.	.
Equisetum arvense	.	.	.	.	.	.	+	+	.	.	.	.	.	.	.	.	.	+	+	1	+	1	1	+	+
Asparagus acutifolius	.	.	.	.	.	.	+	+	+	.	.	1	1	.	.	+	+	.	+	.	.	+	.	.	+
Anthriscus nemorosa	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	1	+	1	2	1	1	+	1	+
Agrostis castellana	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	2	2	1	1	3	2	1	+	+	+
Asplenium onopteris	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	+	+	+	+	+	+	+	+
Tussilago farfara	.	.	+	.	.	.	.	.	+	.	.	.	.	.	.	+	+	+	.	1	+	+	+	.	.
Rubia peregrina	.	.	.	.	.	.	1	+	.	.	.	.	.	.	.	.	.	.	.	1	+	+	+	1	+
Adiantum capillus-veneris	.	.	.	.	.	.	.	.	.	.	1	1	+	.	1	1	1	1	+	.	.	.	.	.	.
Equisetum ramosissimum	1	1	1	.	+	.	.	.	+	.	.	.	1	1	.	.	.	.	.	.	.	.	.	.	.
Allium subhirsutum	.	+	.	.	.	.	.	1	1	1	.	1	.	+	1	.	.	.	.	.	.	.	.	.	.
Scutellaria columnae subsp. gussonei	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	1	+	.	+	.	+	.	+
Agrostis stolonifera	.	.	.	.	.	.	.	.	1	.	1	1	+	.	1	.	.	.	.	.	.	.	.	.	.
Clinopodium arundanum	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	+	+	+	+	.	.
Ruscus aculeatus	.	.	.	.	.	.	.	.	+	.	.	+	.	.	.	.	.	.	.	.	.	.	.	+	+
Nerium oleander	.	.	.	.	.	2	1	2	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Allium triquetrum	.	.	.	.	.	.	.	.	1	.	.	1	1	.	1	.	.	.	.	.	.	.	.	.	.
Salix purpurea	.	1	.	1	1	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Parietaria judaica	.	.	.	.	.	.	.	.	.	.	1	1	.	2	+	.	.	.	.	.	.	.	.	.	.
Convolvulus silvaticus	.	.	.	.	.	.	.	.	1	.	.	1	.	1	1	.	.	.	.	.	.	.	.	.	.
Dittrichia viscosa	1	1	.	1	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Torilis africana	.	.	+	.	.	+	+	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Epilobium parviflorus	.	.	.	.	.	.	.	.	.	.	+	+	.	2	+	.	.	.	.	.	.	.	.	.	.
Arum italicum	.	.	.	.	.	.	.	.	.	+	.	.	.	+	1	.	.	.	.	.	.	.	.	.	.
Prunella vulgaris subsp. vulgaris	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	+	+	.	.
Geranium versicolor	.	.	.	.	.	1	+	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Pulicaria dysenterica	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	+	+	.	.	.	.	.	.
Stachys sylvatica	.	.	.	.	.	.	1	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Ajuga reptans	.	.	.	.	.	.	+	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Viola reichenbachiana	.	.	.	.	.	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Galium aparine	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Angelica sylvestris subsp. sylvestris	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Cyclamen repandum subsp. repandum	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Ficaria verna	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Euphorbia meuselii	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Smilax aspera	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Poa trivialis	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Rosa canina	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.
Cirsium creticum subsp. triumfettii	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Laurus nobilis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.
Geranium purpureum	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.

).

These riparian woods are characterized by the clear dominance of A. glutinosa, linked to ravine environments and to narrow floodplains of perennial waterways that flow in the high-hilly belt, along the bottom of deep valleys, with a somewhat humid and cool microclimate. It is a forest vegetation with closed and continuous structure, with coverage close to 100% and heights even over 20 m, and with a rather sparse herbaceous layer. In addition to the presence of the ferns mentioned previously, the coenosis is enriched with some meso-hygrophilous species, such as Fraxinus ornus, Ficus carica, Sambucus nigra, Carex pendula, and Lamium pubescens.

Distribution: This community is localized in the Peloritani Mountains (Eastern-Sicily), in particular in the upper part of the catchment area of the Fiumara d’Agrò, in the territory of Antillo (Torrente Fonderia, C.de Pianammare, Rosignolo, Pinazzo, etc.), S. Paolo river (Francavilla di Sicilia), Alcantara river. Along the waterways on the Tyrrhenian side of the Peloritani Mounts, there are residual and point-like locations, particularly in Fiumara Madridi (Fondachelli Fantina) and in the Mela Torrent (S. Lucia del Mela), which show floristically impoverished fragments.

Landscape context: In optimal conditions, the association takes catenal contact with the thermophilous deciduous oak woods of the Quercetalia ilicis. This coenosis constitutes the most structured aspect of an edapho-hygrophilous and umbrophilic series, which outlines large sections of waterways in the high-hilly part, in particular when they flow on the bottom of fresh and wet, deepvalleys. Along the riverbed, it can come into contact with the Platano-Salicetum gussonei Brullo and Spampinato 1990, on alluvial accumulations located in the most open part of the waterstreams, in particular in the larger loops or in the downstream part; on the steep, metamorphic slopes that characterize this territory, they are connected on a large scale, with the climatic series of the Erico-Querco virgilianae sigmetum [89].

Notes: The Peloritani district coincides with the north-eastern part of Sicily, which is characterized by the occurrence of several exclusive endemic taxa [84,90,91]. The riparian woodland communities of the Peloritani (Sicily), together with the Alnus glutinosa communities of Algeria and Tunisia, can be considered among the southernmost formations of the A. glutinosa distribution area [22,92]. Therefore, given the particular humidity conditions required, these communities are the most sensitive to climate change. In some contexts of the Peloritani, where the perennial waters become intermittent, we have been recording a slow and progressive replacement of A. glutinosa with Platanus orientalis, the latter more thermophilic and tolerant to intermittently flowing waters. Previously, Alnus glutinosa communities of the north-eastern part of Sicily were included by Brullo and Spampinato [62] in the subassociation Platano-Salicetum gussonei alnetosum (Platanion orientalis alliance). In relation to the Alnus glutinosa-dominance, with very high A. glutinosa cover values and floritic composition, we propose a change of position (from subassociation to association), and a change in the syntaxonomic framework from Platanion orientalis to Osmundo-Alnion glutinosae (Art.26, Art.27).

Figure 6. Plant communities and diagnostic species of the Alnus glutinosa riparian woodlands in Sicily: (1) Platano-Alnetum glutinosae (Fiume Alcantara, Tyrrhenian side of the Peloritani Mountains); (2) Salix gussonei, diagnostic endemic species of the Platano-Alnetum glutinosae; (3) Platano-Alnetum glutinosae (Fiume Alcantara—Ionic side of the Peloritani Mountains); (4) Platano-Alnetum glutinosae (Fiume Mela—Tyrrhenian side of the Peloritani Mountains); (5) Platanus orientalis, characteristic species of the Platano-Alnetum glutinosae; (6–8) Platano-Alnetum glutinosae (Antillo—Monti Peloritani) (Photo credits: L. Gianguzzi (1–8).

Figure 6. Plant communities and diagnostic species of the Alnus glutinosa riparian woodlands in Sicily: (1) Platano-Alnetum glutinosae (Fiume Alcantara, Tyrrhenian side of the Peloritani Mountains); (2) Salix gussonei, diagnostic endemic species of the Platano-Alnetum glutinosae; (3) Platano-Alnetum glutinosae (Fiume Alcantara—Ionic side of the Peloritani Mountains); (4) Platano-Alnetum glutinosae (Fiume Mela—Tyrrhenian side of the Peloritani Mountains); (5) Platanus orientalis, characteristic species of the Platano-Alnetum glutinosae; (6–8) Platano-Alnetum glutinosae (Antillo—Monti Peloritani) (Photo credits: L. Gianguzzi (1–8).

• 4.1. Eupatorio corsici-Alnetum glutinosae (Litard. 1928) Dierschke 1975 (Cluster 4.1a)

Holotypus: Rel. 1, Tab. 1, p. 232 [19].

Diagnostic species: Eupatorium cannabinum subsp. corsicum, Buxus sempervirens, Mentha aquatica, Rosa sempervirens, Convolvulus sepium, Galium album, Populus nigra, Salix cinerea, Vitis vinifera, Laurus nobilis, Smilax aspera, Viburnum tinus.

Constant species: Alnus glutinosa, Athyrium filix-femina, Brachypodium sylvaticum, Clematis vitalba, Ficus carica, Fraxinus ornus, Hedera helix subsp. helix, Hypericum hircinum, Rubus ulmifolius.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Eupatorium cannabinum subsp. corsicum, Carex pendula, Equisetum arvense, Oenanthe crocata, Rorippa palustris.

Structure and ecology: These riparian woods develop at low altitudes (up to about 450 m a.s.l), mainly along watercourses, or stretches of watercourses, with steep slopes, where torrential waters flow in narrow, more or less recessed streambeds. In these systems, where stony or rocky banks predominate, the more or less oligotrophic waters carry coarse sediments, while the presence of fine materials is weak. These woods grow in conditions of Mediterranean macro-bioclimate, Mediterranean main-seasonal oceanic bioclimate, with thermotypes generally ranging from the upper thermomediterranean to the upper mesomediterranean and ombrotypes generally subhumid. These riparian alder woods, more or less narrow, are dominated by A. glutinosa, accompanied by Fraxinus ornus, sometimes by Laurus nobilis. Buxus sempervirens and Ficus carica can structure the shrub layer. In the herbaceous and liana layer, Eupatorium cannabinum subsp. corsicum, Hypericum hircinum, Carex microcarpa, Osmunda regalis, Athyrium filix-femina, Clematis vitalba, and Dioscorea communis are common, while the presence of Polystichum setiferum is more punctual. The floristic composition of this community is also structured (although moderately) by species belonging to the Fagetalia sylvaticae and more sporadically to that of Quercetea ilicis.

Distribution: Crystalline Corsica.

Landscape context: It represents the head of the thermo-mesomediterranean series, oligotrophic and edaphohygrophilous, of the Eupatorium corsici-Alno glutinosae sigmetum.

Notes: This group includes most surveys of Dierschke [19] attributed to the Eupatorio corsici-Alnetum glutinosae (Litard. 1928) Dierschke 1975. It also includes surveys of Gamisans [64] from the Cavu valley, and the Prunelli valley (Eupatorio corsici-Alnetum glutinosae Dierschke 1975 lauretosum nobili Gamisans 2013).

Erigeron bonariensis and Platanus hispanica have been diagnosed by JUICE, but they were excluded from this list because them are invasive species in Corsica (respectively Category Major and Alert) [93].

• 4.1. Eupatorio corsici-Alnetum glutinosae (Litard. 1928) Dierschke 1975 scolopendrietosum nom. nov. hoc loco (Cluster 4.1b)

Syn.: Scolopendrio officinalis-Alnetum glutinosae Gamisans 2013 subass. typicum or scolopendrietosum, subass. populetosum nigrae; Scrophulario auriculatae-Alnetum glutinosae Gamisans 2013 subass. ficetosum caricae, subass. geranietosum nodosi.

Holotypus: Rel. 258, Tab. 16 [64].

Diagnostic species: Alnus cordata, Buxus sempervirens, Cyclamen hederifolium, Equisetum arvense, Eupatorium cannabinum subsp. corsicum, Galium album, Geranium nodosum, Helleborus argutifolius, Hypericum hircinum, Mentha aquatica, M. suaveolens subsp. insularis, Petasites albus, Rosa sempervirens, Salix cinerea, Scrophularia nodosa.

Constant species: Alnus glutinosa, Athyrium filix-femina, Brachypodium sylvaticum, Clematis vitalba, Crataegus monogyna, Hedera helix, Ilex aquifolium, Mycelis muralis, Polystichum setiferum, Pteridium aquilinum, Ranunculus lanuginosus, Rubus ulmifolius, Sambucus nigra, Viola reichenbachiana.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Scolopendrium officinale, Scrophularia nodosa, Scrophularia auriculata, Symphytum bulbosum, Adiantum capillus-veneris.

Structure and ecology: These riparian woods are mostly located in Alpine Corsica (lustrous schists zone) characterized by very complex geological units and they are marked by schists, calcschists, limestones and green rocks (metabasaltes, metagabbros, gabbros, serpentinites). They are structured along watercourses or streams where the streambed is often entrenched within more or less narrow valleys, in an altitudinal belt mainly between 100 and 900 m a.s.l. and seem to be distributed more around a bioclimatic belt characterized by meso-temperate thermotypes (sub-Mediterranean variant) with humid ombrotypes. These riparian forests are dominated by A. glutinosa, accompanied in the shrub layer by Buxus sempervirens, Ilex aquifolium, Sambucus nigra, Corylus avellana, Ostrya carpinifolia and sometimes by Alnus cordata. The herbaceous layer is marked by the presence of Hypericum hircinum, Eupatorium cannabinum subsp. corsicum as well as by the high frequency of aerohygrophilous ferns, such as Athyrium filix-femina, Polystichum setiferum, and accompanied by species of Fagetalia sylvaticae.

Distribution: Mainly Alpine Corsica (San Petrone, Tenda and Cap Corse massifs).

Landscape context: Catenal contact with, for example, formations of Castanea sativa, Quercus pubescens, Q. ilex.

Notes: This group includes some relevés of Dierschke [19] attributed to the Eupatorio corsici-Alnetum glutinosae (Litard. 1928) Dierschke 1975 and other relevés of Gamisans [64] belonging to the Scolopendrio officinalis-Alnetum glutinosae Gamisans 2013 and the Scrophulario auriculatae-Alnetum glutinosae Gamisans 2013. These last two syntaxa are attributed by this author to the riparian forests of the San Petrone and Cap-Corse massifs developing on neutro-basic soils. In particular, they are characterized by the absence of Osmunda regalis, while there are Scrophularia auriculata, Symphytum bulbosum, Scolopendrium officinale, Adiantum capillus-veneris, Scrophularia nodosa, Petasites albus. On the basis of these floristic and ecological features, Gamisans [64] proposed to gather together these two syntaxa within a new sub-alliance (Petasito albi-Adiantenion capillus-veneri Gamisans 2013), which differed from the riparian forests of the Hyperico hircini-Alnenion glutinosae developing on acid soils and characterizing crystalline Corsica. These two sub-alliances were grouped together by this author in the Caricion microcarpae Gamisans (1968) 1977; Osmundo regalis-Alnion glutinosae (Br.-Bl. and al. 1956) Dierschke and Rivas-Martínez was considered here as a West Mediterranean calcifuge unit. This conception was also followed by Reymann et al. [94]. The results of the analyses (clusters) show that the communities of Cluster 4.1a and those of Cluster 4.1b are very similar, signifying the high floristic proximity between the surveys of Eupatorio corsici-Alnetum glutinosae (Litard. 1928) Dierschke 1975 and those of Scolopendrio officinalis-Alnetum glutinosae Gamisans 2013 and Scrophulario auriculatae-Alnetum glutinosae. This similarity leads us to consider this subgroup 4.1b as a subassociation (Eupatorio corsici-Alnetum glutinosae scolopendrietosum). This floristic similarity shows the affinity of these communities to the Osmundo regalis-Alnion glutinosae and better legitimizes their linkage within this alliance and the Hyperico hircini-Alnenion glutinosae. These results are in accordance with Mucina et al. [12], who do not consider the Caricion microcarpae and include it as heterotypic synonym for the Osmundo regalis-Alnion glutinosae. Platanus hispanica was diagnosed by JUICE, but it was removed from this list because it is an invasive species in Corsica (Category: Alert) [93].

• A2. Struthioptero-Alnenion glutinosaesuball. nov. hoc loco (Cluster A2)

Mesophilous woods of central Italy and the Corsican mountains

Holotypus: Carpino betuli-Alnetum glutinosae ass. nov. hoc loco

Diagnostic species: Struthiopteris spicant, Osmunda regalis, Athyrium filix-femina, Ilex aquifolium, Hypericum androsaemum, Carex remota, Allium pendulinum, Anemonoides nemorosa, Carpinus betulus, Melica uniflora, Physospermum cornubiense, Quercus ilex.

Characteristic species: Struthiopteris spicant, Carex pallescens, Hypericum androsaemum, Ilex aquifolium, Stachys sylvatica, Gentiana asclepiadea, Athyrium filix-femina, Lonicera periclymenum.

• 5. Glechomo sardoae-Alnetum glutinosae Arrigoni 1986 (Cluster 5, Figure 5)

Syn.: Carici microcarpae-Alnetum glutinosae Foggi, Cartei, Pignotti, Viciani, Dell’Olmo et Menicagli 2006.

Holotypus: Rel. 24, Tab. 8 [37].

Diagnostic species: Epilobium lanceolatum, Osmunda regalis.

Constant species: Alnus glutinosa, Hedera helix subsp. helix, Athyrium filix-femina, Polystichum setiferum, Pteridium aquilinum subsp. aquilinum, Rubus ulmifolius.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Epilobium lanceolatum, Polystichum setiferum, Glechoma sardoa.

Structure and ecology: Edapho-hygrophilous mesowoods (10–20 m high), that grows on siliceous substrata (granites, granodiorites and metamorphytes) along the rivers of more or less recessed deep valleys. In Sardinia, it is scattered in the mountain belt at 800–1600 m of elevation, while in the Tuscan archipelago it grows in ditches constantly supplied by the water table at elevations between 250 and 600 m a.s.l. They are mainly distributed between meso-mediterranean and temperate submediterranean bioclimates with ombrotypes between the upper subhumid and the lower humid. Floristically, the tree layer is characterized by the dominance of A. glutinosa with the scattered presence of Taxus baccata and Ilex aquifolium in Sardinia, and Quercus ilex and Ostrya carpinifolia in Tuscany. The shrubby and liana layers are mainly represented by Hypericum hircinum subsp. hircinum, Rubus gr. ulmifolius and Hedera helix, while the herbaceous layer is characterized by Carex macrocarpa, endemic to Sardinia, Corsica and the Tuscan archipelago, and by a pool of hygrophilous-calcifuge ferns, such as Polystichum setiferum, Pteridium aquilinum subsp. aquilinum, Athyrium filix-femina, Carex remota, Cystopteris dickieana, C. fragilis and Dryopteris pallida. In Sardinia, several Cyrno-Sardinian endemics, such as Glechoma sardoa, Paeonia corsica, Aquilegia nugorensis and A. barbaricina, are also characteristic of this community.

Distribution: In Sardinia, it is exclusive to the Gennargentu massif (CE Sardinia), a mountain range that, for its degree of isolation and floristic peculiarities, is considered an independent biogeographical sector [95]. In Tuscany, it occurs in the deep valleys of Monte Capanne on the Island of Elba, and also in the Island of Giglio.

Landscape context: It is part of the calcifuge and oligotrophic Sardinian geosigmetum of the mesotemperate-supratemperate bioclimatic belt and the supramediterranean wet and calcifuge Galio scabri-Querceto ilicis geosigmetum [50,88]. In optimal conditions, the association is in contact with the Sardinian climatophilous deciduous oak woods of the Glechomo sardoae-Quercetum congestae [96] or more rarely with the edapho-xerophilous microforests of the Juniperetum nanae subass. cerastietosum boissieriani [61]. Spatial contacts in the Islands of Elba and Giglio are with the climatophilous olm-oak woods referred to as the Galio scabri-Quercetum ilicis and with the edafo-hygrophylous woods of the Polysticho setiferi-Ostryetum carpinifoliae association.

Notes: This association, characterized by a high percentage of Paleotemperate species and orophilous Cyrno-Sardinian endemics, represents the western-southernmost limit of the Struthioptero-Alnenion glutinosae new sub-alliance, which includes the mesophilous plant communities of central Italy, and the Sardinian and Corsican mountains. The conservation interest of this association is also confirmed by the frequent presence of centenary alder trees that characterize some formations with an old-growth character [97]. Otherwise, the delimitation of this community with the rest of the Cyrno-Sardinian associations is within the suball. Hyperico hircini-Alnenion glutinosae is still problematic, and further investigation would therefore be advisable.

• 6. Gentiano asclepiadeae-Alnetum glutinosae (Litard. and Malcuit 1926) Gamisans 1977 corr. Renaux et al. (2019) (Cluster 6)

Syn.: Athyrio filicis-feminae-Gentianetum asclepiadeae Gamisans 1977 nom. illeg. (Art. 3k, 29b)

Lectotypus: Rel. 14, Tab. 37, Gamisans 1975 and 1977: 174 (subassociation gentianetosum asclepiadeae or typicum); Subassociation doronicetosum corsici, lectotypus: Rel. 2, Tab. 37, Gamisans 1975 and 1977: 174; Subassociation conopodietosum denudati Gamisans, holotypus: Rel. 75, Tab. 20.

Diagnostic species: Acer pseudoplatanus, Allium pendulinum, Allium ursinum, Aquilegia dumeticola, Conopodium majus, Cyclamen repandum subsp. repandum, Doronicum corsicum, Galium rotundifolium, Gentiana asclepiadea, Helleborus argutifolius, Ilex aquifolium, Pinus nigra subsp. laricio, Potentilla micrantha, Viola riviniana, Athyrium filix-femina, Cyclamen hederifolium, Festuca heterophylla, Ficaria verna, Mercurialis perennis, Moehringia trinervia, Oenanthe pimpinelloides, Sanicula europaea, Saxifraga rotundifolia, Solidago virgaurea.

Constant species: Alnus glutinosa, Carex microcarpa, Fraxinus ornus, Melica uniflora, Ranunculus lanuginosus.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Gentiana asclepiadea, Athyrium filix-femina, Oreopteris limbosperma.

Structure and ecology: These riparian alder woods are distributed along watercourses or stretches of watercourses with a torrential regime, mainly within crystalline Corsica, in an altitudinal belt above 600 m a.s.l up to around 1150 m a.s.l. They seem to be distributed in correspondence of a bioclimatic belt characterized by upper meso-temperate/lower supra-temperate (sub-mediterranean variant) and sometimes lower supramediterranean thermotypes, with humid ombrotype. These more or less sparse riparian woodlands are dominated by A. glutinosa, Fraxinus ornus and Acer pseudoplatanus, which have more discrete cover values, and Pinus laricio subsp. laricio can be found more rarely. Ilex aquifolium is frequent in the shrub layer, and the herbaceous layer is characterized in particular by the presence of Athyrium filix-femina, Gentiana asclepiadea, Carex microcarpa, Allium ursinum, together with other species of Fagetalia sylvaticae.

Distribution: High valleys of Golu, Tavignanu, Prunelli, Vecchio and valley of Manganellu, etc. (Corsica).

Landscape context: catenal contact with formations of Fagetalia sylvaticae, especially forests of Pinus laricio subsp. laricio and Fagus sylvatica.

Notes: This association was previously included in Hyperico hircini-Alnenion glutinosae Dierschke 1975 where it represented the communities growing at the highest altitudes [64,65,94]. Three subassociations were distinguished there. The inclusion of this association in the new suballiance proposed in this paper (Struthioptero-Alnenion glutinosae) reflects the mesophilous conditions in which these communities develop, which are marked by the high frequency of Fagetalia sylvaticae species. Gamisans (op.cit) also pointed out the high frequency of these species, so the question of whether this association belongs to these units could be raised. No subassociation has been highlighted by the analysis.

• 7. Carici pallescentis-Alnetum glutinosae Landi and Angiolini 2010 (Cluster 7, Figure 7)

Holotypus: Rel. 13, Tab. III [51].

Diagnostic species: Anemonoides nemorosa, Brachypodium rupestre, Castanea sativa, Hypericum androsaemum, Ilex aquifolium, Isolepis cernua, Juncus articulatus subsp. articulatus, Lysimachia vulgaris, Molinia arundinacea, Osmunda regalis, Physospermum cornubiense, Rubus hirtus, Sorbus torminalis, Struthiopteris spicant, Teucrium scorodonia, Frangula alnus subsp. alnus, Fraxinus ornus, Myosotis scorpioides, Prenanthes purpurea.

Constant species: Alnus glutinosa, Athyrium filix-femina, Brachypodium sylvaticum, Carex remota, Hedera helix, Pteridium aquilinum.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Struthiopteris spicant, Carex pallescens, Hypericum androsaemum, Ilex aquifolium.

Structure and ecology: A. glutinosa woods, with Fraxinus ornus, Castanea sativa and Populus tremula. The shrub layer is dominated by Ilex aquifolium, Hypericum androsaemum and, less frequently, by Frangula alnus, Dryopteris affinis, Rubus hirtus and Salix cinerea. The herbaceous layer is dominated by Osmunda regalis, Athyrium filix-femina, Struthiopteris spicant, Carex remota and C. pallescens. Together with entities belonging to the genus Sphagnum sp. pl., these species highlight the meso-oligotrophic and calcifugous character of the coenosis [98,99]. The elevated abundance of Molinia arundinacea and/or the presence of Phragmites australis in some relevés, on the other hand, indicates a more heliophytic nature. On soils where the slope increases or even in the spring swamps where the surfacing water decreases, these woods undergo successive stages of degeneration with the substitution of some hygrophilous species such as Struthiopteris spicant and Molinia arundinacea with the less hygrophilous ones such as Pteridium aquilinum [100]. This vegetation is linked to meso-oligotrophic and acidophilous riparian environments in ditches and streams constantly supplied by the water table, and with spring swamps connected to them. These environments can be found in hilly mountainous areas between 150 and 600 m a.s.l. characterized, according to Pesaresi et al. [79], by a Mediterranean oceanic pluviseasonal bioclimate and, only marginally (Apuan Alps phytocoenoses), by a temperate oceanic (submediterranean) one; the thermotype ranges from the lower mesomediterranean to the lower supratemperate and ombrotypes between the lower subhumid and the lower humid.

Distribution: Tyrrhenian side of central Italy (Monte Pisano, Poggio di Montieri, hills around the Farma-Merse basin and Monte Leoni and, in a marginal form, Apuan Alps; the association is probably present also in northern Latium) [51,101].

Landscape context: The phytocoenoses identified in southern Tuscany are in contact with woods assigned to Physospermo cornubiensis-Quercetum petraeae Oberdorfer et Hofmann 1967 [102] attributable to the alliance Erythronio-Quercion petraeae Ubaldi (1988) 1990 (Quercetalia pubescenti-petraeae Klika 1933 corr. Moravec in Béguin et Theurillat 1984).

Notes: The Mediterranean and Eurasian chorotypes are dominant. The frequency of species associated with temperate climates (e.g., Anemone nemorosa, Struthiopteris spicant and Carex pallescens), the absence of the Mediterranean Hypericum hircinum, typical of the suballiance Hyperico hircini-Alnenion glutinosae substituted by H. androsaemum, an oceanic species, and the participation of Mediterranean species, place this association on the boundary between the Mediterranean and Eurasian phytogeographic regions [103].

Figure 7. Plant communities and diagnostic species of the Alnus glutinosa riparian woodlands in Italian Peninsula: (1) Osmunda regalis, in the Carici pallescentis-Alnetum glutinosae (Toscana); (2) Carpino betuli-Alnetum glutinosae (Mignone, Canale Monterano—Lazio); (3,4) Euphorbio-Alnetum glutinosae, respectively, in Sila Grande and Torrente Vasi (Calabria); (5) Euphorbia corallioides, characteristic species of the Euphorbio-Alnetum glutinosae (Calabria); (6) Angelico sylvestris-Alnetum glutinosae (Torrente Sarmento, Pollino Mounts—Calabria); (7,8) Polysticho-Alnetum glutinosae, respectively, in the Serre Calabre and Torrente Ferraino (Aspromonte—Calabria); Photo credits: O. Caldarella (1), M. Cutini (2), G. Spampinato (3), L. Gianguzzi (4,5,7,8).

Figure 7. Plant communities and diagnostic species of the Alnus glutinosa riparian woodlands in Italian Peninsula: (1) Osmunda regalis, in the Carici pallescentis-Alnetum glutinosae (Toscana); (2) Carpino betuli-Alnetum glutinosae (Mignone, Canale Monterano—Lazio); (3,4) Euphorbio-Alnetum glutinosae, respectively, in Sila Grande and Torrente Vasi (Calabria); (5) Euphorbia corallioides, characteristic species of the Euphorbio-Alnetum glutinosae (Calabria); (6) Angelico sylvestris-Alnetum glutinosae (Torrente Sarmento, Pollino Mounts—Calabria); (7,8) Polysticho-Alnetum glutinosae, respectively, in the Serre Calabre and Torrente Ferraino (Aspromonte—Calabria); Photo credits: O. Caldarella (1), M. Cutini (2), G. Spampinato (3), L. Gianguzzi (4,5,7,8).

• 8. Carpino betuli-Alnetum glutinosae (Di Pietro et al. 2010) Sciandrello et al. nom. nov. hoc loco (Cluster 8, Figure 7)

Syn.: Polysticho-Alnetum glutinosae [43]; Polysticho-Alnetum glutinosae [44].

Holopypus: Rel. 1, Tab. 12 [43].

Diagnostic species: Carpinus betulus, Quercus petraea, Dactylorhiza maculata, Dioscorea communis, Lonicera caprifolium.

Constant species: Acer campestre, Alnus glutinosa, Athyrium filix-femina, Brachypodium sylvaticum, Carex pendula, Carex remota, Circaea lutetiana, Clematis vitalba, Corylus avellana, Fraxinus ornus, Hedera helix subsp. helix, Melica uniflora, Mycelis muralis, Osmunda regalis, Polystichum setiferum, Ranunculus lanuginosus, Rubus ulmifolius, Ruscus aculeatus, Viola reichenbachiana.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Polysticum setiferum, Athyrium filix-femina, Struthiopteris spicant, Ilex aquifolium.

Structure and ecology: ravine woodlands which develop on limited spaces in the bottom of the small gorges, on gentle slopes at lower altitude (150–400 m a.s.l.) linked to Mediterranean lower mesomediterranean thermotype and upper subhumid ombrotype. Carpino betuli-Alnetum glutinosae is strongly related to volcanic (ignimbrites) litotypes. These are multilayer communities organised generally on two levels: higher tree level (until 20 m), constantly represented by A. glutinosa, lower tree level (7–8 m), while shrubs and herbaceous layers appear extremely variable. Locally, it is possible to find stands with high wood diversity, in which there is participation of Fagus sylvatica, Quercus petraea, and Q. cerris. Generally, these are facies where the spatial contact with mesophitic deciduous formations is quite evident. These events are favored by particular morphological conditions, such as topographic variability and steep slopes. From a chorological point of view, the new association is characterized by the predominance of Eurasiatic species, followed by the Mediterranean and Boreal ones. This character is also confirmed for other plant communities of the sub-coastal district of the Tuscan-Latium Maremma, as a result of the marked interpenetration between the temperate and mediterranean biocore; this is evidence widely highlighted in the literature [51,104,105,106,107].

Distribution: Northern Latium.

Landscape context: catenal contact with extrazonal mesophytic formations (Fagetalia sylvaticae), locally dominated by Quercus cerris [44,108], in a complex mosaic characterized by the transition between Mediterranean and temperate biocora.

Notes: Some relevés of this association were previously considered as belonging to the Polysticho-Alnetum glutinosae association, described by Di Pietro et al. [43] in the Tolfa Mountains (northern Latium). Similarly, the same can be said for relevés carried out in the same district, reported by Cutini et al. [44] to the Polysticho-Alnetum glutinosae association described in Aspromonte (southern Calabria) [61].

• B. Ligustro vulgaris–Alnion glutinosae Poldini, Sburlino and Venanzoni 2015 in Biondi et al. 2015 (Cluster B)

Riparian meso-thermophilous forests of the submediterranean regions of the Northern and Central Apennine Peninsula.

Holotypus: Aro italici-Alnetum glutinosae Gafta and Pedrotti 1996 [55] (p. 414)

Diagnostic species: Aegopodium podagraria, Cornus sanguinea, Rubus caesius, Stachys sylvatica, Urtica dioica, Alliaria petiolata, Angelica sylvestris subsp. sylvestris, Chaerophyllum temulum, Euonymus europaeus, Galium aparine, Geranium versicolor, Geum urbanum, Ligustrum vulgare, Petasites hybridus, Salix alba, Sambucus nigra, Solanum dulcamara.

Characteristic species (according to the literature): Bryonia dioica, Chaerophyllum temulum, Equisetum telmateja, Ligustrum vulgare, Petasites hybridus, Populus alba, P. nigra, Robinia pseudacacia [16].

• 9. Aro italici-Alnetum glutinosae Gafta and Pedrotti 1996 (Cluster 9)

Syn.: Alno-Fraxinetum oxycarpae Tchou 1946 (Francalancia and Macconi 1994)

Holotypus: Rel. 1, p. 414 [55]

Diagnostic species: Alliaria petiolata, Bryonia dioica, Carduus personata, Cornus sanguinea, Elymus caninus, Heracleum sibiricum subsp. ternatum, Lonicera xylosteum, Pulmonaria vallarsae, Aegopodium podagraria, Euonymus europaeus, Myosoton aquaticum.

Constant species: Acer campestre, Alnus glutinosa, Brachypodium sylvaticum, Clematis vitalba, Corylus avellana, Geranium robertianum, Geum urbanum, Ranunculus lanuginosus, Sambucus nigra, Stachys sylvatica, Urtica dioica.

Dominant species: Alnus glutinosa.

Characteristic species (according to [54]: Alliaria petiolata, Angelica sylvestris subsp. sylvestris, Asarum europaeum, Adoxa moschatellina subsp. moschatellina, Cardamine bulbifera, Heracleum sibiricum subsp. ternatum, Lolium giganteum, Stachys sylvatica.

Structure and ecology: These riparian woods occur along the middle-upper section of some river basins in the southern part of the Marche region, at altitude ranging between 560 and 820 m a.s.l., at the edge of fast-flowing watercourses, on constantly moist substrates consisting mainly of coarse alluvial deposits (pebbles mixed with sand). They are characterized by high cover values of black alder, which forms quite a monospecific tree layer, with sporadic and sparse presence of Populus alba, P. nigra, Salix alba. The shrub layer is mainly formed by species of Rhamno-Prunetea, such as Crataegus monogyna, Prunus spinosa, Rubus caesius, Rubus ulmifolius, whose presence is probably due to a long-time coppice management [54]. The herbaceous layer is well developed and rich in species; the most frequent and abundant are Alliaria petiolata, Angelica sylvestris, Brachypodium sylvaticum, Petasites hybridus, Pulmonaria vallarsae subsp. Apennina, Lolium giganteum, Stachys sylvatica. The level of anthropic disturbance is highlighted by the presence (with, sometimes, high frequence and meaningful cover values), of synanthropic species such as Urtica dioica, Chaerophyllum temulum, and Stellaria media. These communities have, at present, considerably reduced and fragmented extent. The reduction in area is due to the expansion of cultivated areas, in some cases up to the river fringes. According to Pesaresi et al. [79], the area where these communities are distributed is characterized by a thermotype that ranges from lower to upper supratemperate and upper humid ombrotypes.

Distribution: Marche, Lazio, Toscana, Umbria.

Landscape context: Catenal contact with Populus alba and P. nigra communities or with mesophytic formations locally dominated by Quercus cerris and Fagus sylvatica [54].

Notes: These communities had been previously attributed, along with other similar formations found in Liguria and in central Italy, to the association Alno-Fraxinetum oxycarpae Tchou 1946 [46,54,69, 109,110,111], even if most of these authors have expressed several doubts about the real attribution to this association described by Tchou [112] for Southern France, due to both the floristic composition and, in particular, the absence of Fraxinus oxycarpa (see also [40]).

• 10. Aegopodio podagrariae-Alnetum glutinosae (Blasi and Frondoni 1996) Sciandrello et al. nom. nov. hoc loco (Cluster 10)

Syn.: Circaeo lutetianae-Alnetum glutinosae Blasi and Frondoni 1996.

Holopypus: Rel. 10, Tab. 1 [40].

Diagnostic species: Acer campestre, Anthriscus sylvestris, Parietaria officinalis, Plantago major, Poa annua, Veronica montana, Aegopodium podagraria, Alliaria petiolata, Asplenium scolopendrium subsp. scolopendrium, Chaerophyllum temulum, Chelidonium majus, Euphorbia amygdaloides, Lamium maculatum, Poa sylvicola, Primula vulgaris, Ranunculus lanuginosus, Ruscus aculeatus, Silene baccifera, Ulmus minor.

Constant species: Alnus glutinosa, Brachypodium sylvaticum, Circaea lutetiana, Clematis vitalba, Crataegus monogyna, Geum urbanum, Hedera helix subsp. helix, Melica uniflora, Mycelis muralis, Rubus ulmifolius, Sambucus nigra, Urtica dioica, Viola reichenbachiana.

Dominant species: Alnus glutinosa, Hedera helix subsp. helix, Sambucus nigra.

Characteristic species (according to the literature): Alnus glutinosa, Circaea lutetiana, Carex pendula, Carex remota, Stachys sylvatica.

Structure and ecology: Mesophitic riparian woodland of limited altitudes, located at the bottom of ravines, generally on deep soils characterized by fine sediments. They occur at an altitude between 150 and 800 m, in territories with a Mediterranean lower mesomediterranean thermotype and upper subhumid ombrotype. Sporadically found in riverbeds with abundant coarse debris [40]. The arboreal layer, always with high coverages (>90%), is characterized by A. glutinosa and can be locally accompanied by Carpinus betulus and Corylus avellana. The shrub layer is generally present and abundant, and it is characterized by Corylus avellana and Ulmus minor. The herbaceous layer is characterized by Aegopodium podagraria, Circaea lutetiana, Carex pendula, Stachys sylvatica, Viola reichenbachiana, Melica uniflora. From a chorological point of view, the Aegopodio-Alnetum glutinosae is a vegetation characterized by the interpenetration between species with Eurasian and Pontic (eastern) distribution, locally with a significant presence of the wide distribution type.

Distribution: Northern Latium.

Landscape context: Catenal contact with extrazonal mesophytic formations (Fagetalia sylvaticae), locally dominated by Quercus cerris and Carpinus betulus [44], in a tension area characterized by complex mosaics due to the transition between Mediterranean and temperate biocora.

Notes: communities strongly conditioned by anthropogenic disturbance. Generally, these are populations of limited extension, structurally present also in the bushes form. Robinia pseudoacacia has been diagnosed by JUICE, but it has been removed from the list of diagnostic species because it is an invasive alien species.

These communities have been described by Blasi and Frondoni [40] as Circaeo lutetianae-Alnetum glutinosae. In fact, Circaeo-Alnetum has to be considered an illegitimate name due to being homonymous (according to Art. 31 of the ICPN); it was already used by Oberdorfer [113], by Navarro [114] for the Iberian Peninsula and, as noticed by Di Pietro et al. [43] by Fukarek [115] for the description of riparian communities in Bosnia-Herzegovina. Therefore, the introduction of the nomen novum appears necessary in order to introduce a valid name for this syntaxon.

• 11. Geranio nodosi-Alnetum glutinosaeass. nov. hoc loco subass. typicum (Cluster 11)

Holotypus: Rel. 27,

Table 2. Geranio nodosi-Alnetum glutinosae ass. nov. hoc loco. Appendix A.

Rel. Numbers	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27*	28	29	30	31
Rel. Numbers Cluster	310	311	312	313	314	316	324	332	353	354	355	356	357	358	359	360	361	362	363	364	365	366	367	368	369	370	371	372	373	374	375
Area (m2)	150	40	100	100	50	100	100	50	100	200	100	20	150	100	100	50	30	100	50	50	50	50	30	50	80	50	150	100	50	80	80
Aspect	W	W	NE	NW	NW	NE	-	-	-	-	-	-	W	-	-	-	-	-	N	N		-	-	-	W	E	-	-	SE	-	-
Slope (°)	35	25	25	20	15	20	0	0	5	0	0	0	35	0	5	0	5	0	15	15	5	5	5	0	10	20	0	0	10	0	0
Cover (%)	95	90	95	90	85	90	100	90	80	80	50	70	95	95	95	80	95	95	95	95	100	95	100	80	95	95	95	90	90	95	80
Altitude (m s.l.m.)	703	700	862	598	711	843	813	850	839	861	747	709	649	783	739	729	709	521	539	559	639	671	659	629	589	587	689	609	531	533	549
Richness floristic	18	20	18	10	9	19	26	25	35	30	16	11	28	24	18	18	14	24	17	19	16	16	18	12	19	16	33	26	28	18	29
Char. Ass.
Geranium nodosum	2	2	1	+	.	2	2	+	1	1	.	2	1	1	2	2	.	r	.	.	+	+	r	.	+	r	2	1	1	+	r
Cardamine heptaphylla	.	.	.	.	.	.	.	r	r	+	+	.	.	+	+	+	.	.	+	.	.	.	.	.	.	.	r	.	.	.	.
Char. Ligustro vulgaris-Alnion glutinosae
Circaea lutetiana	1	+	1	.	.	+	2	1	+	+	r	1	+	.	.	r	+	1	2	+	.	.	1	.	+	+	2	2	.	.	+
Aegopodium podagraria	+	r	.	.	.	.	.	.	.	+	.	.	r	+	2	.	.	.	+	.	.	.	r	.	+	.	1	r	r	+	+
Geum urbanum	+	+	.	.	.	.	+	+	.	.	.	.	+	.	.	.	+	+	+	+	.	.	.	.	.	.	1	.	+	+	+
Rubus caesius	2	1	.	.	.	+	.	r	.	.	.	1	.	.	.	.	.	2	3	2	.	.	.	.	.	+	.	.	+	r	+
Sambucus nigra	+	.	.	.	1	2	+	+	.	.	.	2	1	.	.	.	.	+	.	.	.	.	.	.	.	.	1	1	.	.	.
Alliaria petiolata	r	.	.	.	.	1	.	.	.	r	.	.	+	.	.	.	.	1	+	.	+	.	.	.	.	.	.	.	.	.	r
Stachys sylvatica	.	.	2	.	.	r	1	.	r	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.
Cardamine impatiens	.	.	.	.	.	.	+	.	+	+	r	.	.	.	.	r	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Chaerophyllum temulum	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	r	.	.	.	.	.	.
Char. Alno glutinosae-Populetea albae and Populetalia albae
Alnus glutinosa	5	4	4	5	4	4	5	5	4	4	3	3	4	3	3	4	5	4	4	5	5	5	5	4	4	4	4	4	4	5	3
Brachypodium sylvaticum subsp. sylvaticum	+	3	.	.	+	.	.	.	1	.	.	1	2	.	.	.	.	1	.	+	2	.	.	.	.	1	r	.	1	1	2
Carex pendula	+	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	+	.	1	+	+
Solanum dulcamara	.	.	.	.	.	r	+	.	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.
Carex remota	.	.	.	.	.	.	.	.	2	1	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Salix alba	.	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	2	.	2	.	.
Fraxinus angustifolia subsp. oxycarpa	.	.	.	.	.	.	.	.	.	.	.	.	.	2	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Saponaria officinalis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.
Other species
Melica uniflora	+	1	1	1	.	+	1	1	+	1	+	2	+	1	1	.	.	1	+	.	.	+	1	r	r	+	1	+	r	.	1
Hedera helix subsp. helix	.	.	.	2	.	.	.	.	.	.	1	2	+	+	.	+	+	.	.	.	.	1	1	r	1	1	1	1	+	+	1
Geranium robertianum	.	+	+	.	.	+	.	3	+	.	+	.	+	.	+	1	.	.	.	.	r	.	r	.	r	r	+	+	+	.	+
Corylus avellana	.	.	.	.	1	.	.	+	.	.	1	.	1	1	1	.	+	.	.	1	2	1	3	1	3	3	1	1	.	.	.
Dryopteris filix-mas	r	.	1	1	1	+	+	.	.	r	.	.	.	.	+	.	+	.	.	1	.	+	.	.	.	.	1	1	.	r	+
Viola reichenbachiana	.	.	+	.	.	.	+	r	.	+	.	.	.	1	.	r	.	.	.	.	.	.	+	r	+	r	r	r	r	.	+
Ranunculus lanuginosus	2	+	.	.	.	.	+	1	1	+	r	.	1	+	.	.	.	.	.	.	r	r	+	+	.	.	.	.	.	.	.
Mycelis muralis	+	.	+	.	.	+	+	1	.	.	.	.	.	.	r	r	.	.	r	.	.	.	.	.	.	r	+	r	r	.	.
Acer pseudoplatanus	+	1	.	.	.	.	.	.	r	+	+	.	2	+	.	+	.	.	.	.	2	.	.	.	.	.	.	1	2	.	.
Clematis vitalba	.	.	.	.	.	.	+	+	.	.	.	.	.	.	.	.	.	.	.	+	.	r	r	.	.	.	+	+	r	+	r
Euphorbia dulcis	.	+	.	.	.	.	.	.	r	.	r	.	.	r	r	r	.	+	.	.	.	.	.	.	r	.	r	+	.	.	.
Saxifraga rotundifolia	+	.	+	+	.	.	.	.	r	r	.	.	r	+	r	.	.	.	.	.	.	.	.	.	.	r	.	+	.	.	.
Urtica dioica	.	.	+	.	+	+	.	.	.	+	.	.	.	.	.	1	+	+	.	.	.	.	.	.	.	.	+	.	.	.	+
Fraxinus ornus	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	r	.	.	.	+	+	.	.	.	.	.	r	.	+	r	+
Equisetum arvense	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	1	r	+	1	+	.	+	.	.	.	r
Rubus hirtus	.	.	1	.	3	.	.	.	.	.	.	.	+	.	.	.	2	.	.	.	.	.	.	.	.	.	.	+	+	+	+
Acer campestre	.	2	.	.	.	.	.	1	.	.	.	.	+	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	1	1	+
Lunaria rediviva	.	.	.	.	.	.	.	.	r	.	.	.	.	.	r	+	+	+	1	1	.	.	.	.	.	.	.	.	.	.	.
Cornus sanguinea	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	2	.	.	.	.	2	.	.	.	+	1	+
Chaerophyllum hirsutum (incl. C. calabrum)	.	.	.	.	.	2	r	.	2	.	r	.	.	.	.	.	+	.	.	r	.	.	.	.	.	.	.	.	.	.	.
Cardamine bulbifera	.	.	.	.	.	.	.	1	.	.	r	.	+	+	+	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Fagus sylvatica subsp. sylvatica	.	.	.	.	.	.	.	.	.	1	.	.	.	3	3	+	.	.	.	.	.	.	.	.	.	.	.	.	1	.	r
Petasites albus	.	.	2	.	1	+	.	.	r	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.
Stellaria nemorum subsp. montana	.	.	.	.	.	.	1	.	.	1	1	.	r	1	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Crataegus monogyna	.	1	+	.	.	.	.	.	.	.	.	.	+	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.
Castanea sativa	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	1	r	.	r	.	.	.	r
Anemonoides nemorosa	.	r	.	.	.	.	.	.	r	+	.	.	.	+	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Poa sylvicola	.	.	.	.	.	.	+	.	+	r	.	.	r	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.
Lolium giganteum	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	1	+	+	.	.	.	.	.	.	+	.	.	.
Campanula trachelium	.	.	r	+	.	.	.	.	r	.	.	.	r	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Oxalis acetosella	.	.	.	1	.	.	+	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	+	r	.	.	.	.	.	.	.
Polystichum setiferum	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.	.	.	.	.	.	1	.	.	.	+	.	.	.	.	1
Viola alba subsp. dehnhardtii	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	r	r	r	.
Athyrium filix-femina	.	.	.	.	.	.	1	.	+	.	+	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Equisetum telmateia	.	+	.	.	.	.	+	+	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.
Carex sylvatica	.	.	.	.	.	.	+	+	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.
Carpinus betulus	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	2	1	.	.	1	.	.	.	.	2
Primula vulgaris	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	r	.	.	.	r	.	.
Festuca heterophylla	.	.	.	.	.	.	.	.	+	+	.	.	.	+	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.
Ranunculus repens	.	.	.	.	.	.	+	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	+
Rubus idaeus subsp. idaeus	.	.	.	.	.	.	2	.	.	.	.	.	.	.	.	.	.	.	.	.	3	.	.	.	.	.	1	+	.	.	.
Euphorbia amygdaloides	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	+	+	+
Helleborus viridis subsp. bocconei	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	r	.	r	.	.	.	.	.	r
Impatiens parviflora	.	+	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	r	.	.	+	.	.	.	.	.	.	.	.	.	.
Galeopsis speciosa	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	r	.	.	.	.	.	r	.	.
Senecio ovatus	.	.	.	.	r	.	+	.	r	.	.	.	.	.	.	.	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.
Veronica urticifolia	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	r	r	.	.	.	r	.	.	.
Lamium galeobdolon	.	.	.	.	.	.	.	.	.	.	.	1	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.
Mercurialis perennis	.	.	.	.	.	+	+	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Robinia pseudoacacia	.	.	.	.	.	.	.	.	.	.	.	.	2	.	.	.	.	.	+	.	.	.	.	.	.	.	.	1	.	.	.
Poa nemoralis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	+	.	.	.	.	.	+	.	.	.	.
Thalictrum aquilegiifolium subsp. aquilegiifolium	.	.	.	.	.	.	.	.	+	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.
Parietaria officinalis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	3	.	+	.	.	.	.	.	+	.	.	.	.	.
Scrophularia nodosa	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	r
Asarum europaeum	.	.	.	2	.	.	+	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Dactylis glomerata	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	1	.	1	.	.	.	.	.	.	.	.	.	.	.
Polygonatum multiflorum	.	.	.	.	.	.	.	.	r	.	.	.	.	+	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.
Myosotis sylvatica	.	.	.	.	.	.	.	.	+	+	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Pteridium aquilinum subsp. aquilinum	.	.	.	.	.	.	.	.	+	.	.	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Dioscorea communis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	+	.	.	.	.
Symphytum tuberosum subsp. angustifolium	.	.	.	.	.	+	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Ficaria verna	.	.	.	.	.	.	.	.	+	2	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Solidago virgaurea	r	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Salvia glutinosa	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	r	.
Arctium minus	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	+	.	.	.	.	.	.	.	.	.	.	.
Moehringia trinervia	.	.	.	.	.	.	.	.	.	r	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Juglans regia	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	2	.	.	.	.	2	.	.	.	.
Asplenium trichomanes subsp. quadrivalens	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.
Gentiana asclepiadea	.	.	.	.	.	.	.	.	+	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Rosa arvensis	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.	.	.
Sedum cepaea	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	r	.	.	.	.	.	.	.	.	.	.	.
Rubus ulmifolius	.	.	.	.	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Ficus carica	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.
Agrostis stolonifera	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Prunella vulgaris subsp. vulgaris	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Lathyrus venetus	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.
Rumex sanguineus	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.
Ajuga reptans	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.
Arctium lappa	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Ostrya carpinifolia	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.
Dactylorhiza maculata	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Rosa sempervirens	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Lapsana communis	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Lonicera etrusca	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Prenanthes purpurea	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Prunus avium	.	.	.	.	.	.	.	.	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Clinopodium vulgare	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.
Fragaria vesca subsp. vesca	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.
Emerus major	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.
Chelidonium majus	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Daphne laureola	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Rumex conglomeratus	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Bromopsis ramosa	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	2	.	.	.
Cardamine chelidonia	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Populus tremula	.	.	.	.	.	.	.	.	.	2	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Pulmonaria hirta	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Impatiens noli-tangere	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.
Adoxa moschatellina subsp. moschatellina	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Myosotis scorpioides	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.

, hoc loco.

Diagnostic species: Cardamine heptaphylla, Euphorbia dulcis, Geranium nodosum, Lunaria rediviva, Stellaria nemorum subsp. montana, Oxalis acetosella, Petasites albus, Saxifraga rotundifolia.

Constant species: Alnus glutinosa, Circaea lutetiana, Corylus avellana, Geranium robertianum, Hedera helix subsp. helix, Melica uniflora.

Dominant species: Alnus glutinosa.

Structure and ecology: This riparian vegetation is markedly mesophilous and generally present on siliceous substrata in submontane and mountain environments of the Tuscan Apennines, between 500 and 900 m a.s.l., even if sometimes it can be found on alluvial deposits derived from other geological types. Floristically, the herb layer is characterized by several species of mixed mesophilous and beech woods, such as Geranium nodosum, G. robertianum, Melica uniflora, Circaea lutetiana, Cardamine heptaphylla, and Geum urbanum. The tree layer is dominated by A. glutinosa with low cover values of other mesophilous wood species, such as Acer pseudoplatanus, Carpinus betulus, and Fagus sylvatica, while the dominated tree and shrubby layer are characterized by Sambucus nigra and Corylus avellana. According to Pesaresi et al. [79], the area where these communities are distributed is characterized by a temperate oceanic (weakly submediterranean) bioclimate; the thermotype ranges from lower to upper mesotemperate and ombrotypes between upper subhumid and lower humid.

Distribution: Lucca, Pistoia, Prato and Arezzo Apennines (Tuscany).

Landscape context: The association is in catenal contact with mesophilous deciduous mixed oak woods and chestnut woods of the Quercetalia pubescenti-petraeae, at higher altitudes also with beech woods of Fagetalia sylvaticae.

• 12. Geranio nodosi-Alnetum glutinosae cornetosum sanguineaesubass. nov. (Cluster 12)

Holotypus: Rel. 9,

Table 3. Geranio nodosi-Alnetum glutinosae cornetosum sanguineae subass. nov. hoc loco. Appendix A.

Rel. Numbers	1	2	3	4	5	6	7	8	9 *	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28
Rel. Numbers Cluster	315	317	318	319	320	321	322	323	325	326	327	328	329	330	331	333	334	335	337	339	340	343	344	345	346	347	348	349
Area (m2)	100	50	50	50	30	100	50	50	20	50	45	80	100	50	100	50	50	300	100	70	70	200	80	60	200	100	100	100
Aspect	W	W	NE	N	E	-	-	-	E	SE	SE	-	-	-	-	-	-	N	-	-	NE	-	-	-	NW	-	-	-
Slope (°)	20	5	25	3	30	0	0	0	5	10	45	0	0	0	0	0	0	6	0	0	30	32	3	3	6	2	2	2
Cover total (%)	100	95	90	85	90	95	85	100	100	100	90	90	90	90	90	90	100	100	85	100	95	100	95	90	100	100	90	100
Altitude (m s.l.m.)	240	265	145	283	287	631	173	286	263	263	235	540	540	600	560	740	550	620	330	251	265	520	440	445	630	320	340	380
Richness floristic	25	23	28	25	25	22	25	16	21	30	39	31	32	34	33	29	32	25	23	36	31	32	31	30	46	39	37	28
Char. Ass.
Geranium nodosum	.	1	+	+	+	.	+	1	1	2	+	1	+	1	1	2	1	.	r	+	1	2	1	1	2	.	+	+
Cornus sanguinea	1	.	1	.	.	.	.	1	2	1	+	1	+	+	1	.	2	.	3	1	+	+	1	1	.	+	1	1
Char. Ligustro vulgaris-Alnion glutinosae
Aegopodium podagraria	.	.	.	.	1	.	+	.	3	3	2	+	+	2	3	3	2	.	2	.	3	.	2	1	+	1	.	1
Circaea lutetiana	1	.	+	.	+	1	+	1	1	2	+	1	+	.	1	+	.	1	.	.	.	1	.	.	1	.	+	.
Rubus caesius	.	.	1	.	.	.	.	.	.	1	.	3	1	1	1	.	.	.	2	.	.	2	1	.	.	+	+	2
Geum urbanum	.	+	.	.	+	+	.	.	.	+	+	.	.	.	+	.	.	+	.	+	.	.	.	.	+	.	+	.
Petasites hybridus subsp. hybridus	.	.	.	.	.	.	.	.	.	.	.	+	1	.	.	.	.	.	.	.	r	.	1	2	+	1	+	2
Alliaria petiolata	.	.	.	.	.	+	.	.	.	+	.	.	.	.	2	.	+	.	.	+	r	+	.	.	.	.	+	.
Stachys sylvatica	.	.	.	+	.	+	.	.	.	.	.	1	.	1	.	+	.	.	.	.	.	+	.	.	1	.	.	.
Cardamine impatiens	.	+	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	1	.	.	.	.	.	.	2	.	.	.
Chaerophyllum temulum	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	+	+	+	+	.
Char. Alno glutinosae-Populetea albae and Populetalia albae
Alnus glutinosa	4	4	5	5	4	4	5	4	4	4	4	4	5	4	5	5	5	5	5	3	5	5	5	5	4	4	4	4
Brachypodium sylvaticum subsp. sylvaticum	+	.	+	.	.	.	+	.	.	.	2	+	+	2	1	.	2	+	1	.	+	+	1	1	.	1	+	+
Carex pendula	1	.	1	+	+	.	+	1	.	.	+	.	+	+	1	+	+	.	.	.	.	.	1	1	1	2	+	.
Sambucus nigra	1	1	1	1	.	1	2	+	.	2	.	.	.	.	1	.	.	.	r	1	+	1	.	.	.	+	1	.
Solanum dulcamara	R	.	.	.	.	.	+	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Carex remota	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.
Salix alba	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.	.	.	.	.	.	.	.	1	1	.	.
Populus nigra	.	.	.	.	.	.	.	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	2
Fraxinus angustifolia subsp. oxycarpa	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.
Saponaria officinalis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.
Other species
Hedera helix subsp. helix	3	2	2	2	2	+	1	3	1	2	1	.	.	+	+	.	2	+	3	2	1	+	1	3	1	2	3	+
Clematis vitalba	1	+	1	1	1	1	+	+	1	1	.	+	1	.	.	.	1	1	1	+	.	1	1	1	+	+	+	1
Melica uniflora	+	+	+	+	.	+	+	+	1	1	+	+	+	.	+	1	.	.	.	r	.	+	.	.	2	+	1	1
Corylus avellana	1	1	.	1	2	.	.	1	+	.	1	+	+	+	.	.	.	.	r	r	1	1	1	.	2	1	2	1
Acer campestre	.	+	+	.	+	.	.	.	+	.	+	r	+	1	+	+	+	.	3	1	2	.	.	+	.	+	1	+
Fraxinus ornus	.	1	.	1	+	+	+	.	.	.	.	+	.	1	.	+	1	.	1	1	+	+	2	1	.	+	.	.
Mycelis muralis	.	.	+	+	+	+	.	.	.	.	.	+	+	.	+	+	.	.	+	r	+	+	.	.	+	+	+	1
Rubus ulmifolius	1	+	1	1	1	2	1	.	.	.	+	.	.	2	.	.	.	2	.	+	+	.	.	+	1	.	.	.
Dioscorea communis	+	+	+	+	+	.	.	.	+	+	2	.	+	.	.	.	.	+	.	2	.	.	+	.	.	.	+	.
Polystichum setiferum	2	1	1	.	+	+	+	1	1	1	2	.	.	.	.	.	.	.	.	.	.	2	.	.	+	.	+	.
Crataegus monogyna	.	.	1	1	.	.	.	.	.	.	+	+	+	2	1	.	+	+	+	.	+	.	+	.	+	.	.	.
Geranium robertianum	.	.	.	+	.	1	.	.	.	.	.	1	+	.	.	.	.	1	r	+	.	1	.	.	2	+	+	+
Primula vulgaris	.	.	.	.	.	.	.	.	+	.	.	.	.	+	+	1	+	.	.	+	+	.	+	1	.	+	+	+
Viola reichenbachiana	.	+	1	.	.	.	.	.	.	.	1	.	+	r	.	1	.	.	+	.	.	.	.	1	.	+	+	+
Euphorbia dulcis	.	+	.	.	.	.	.	.	.	.	.	+	+	r	+	+	+	.	.	.	.	+	+	.	+	.	.	.
Ostrya carpinifolia	.	.	.	1	.	.	.	.	.	.	1	2	.	.	.	1	1	1	.	.	2	+	.	1	+	.	.	.
Urtica dioica	+	.	.	.	.	+	+	.	.	1	.	1	.	.	+	.	.	2	.	+	+	.	.	.	1	.	.	.
Symphytum tuberosum subsp. angustifolium	1	.	.	.	.	.	.	.	.	.	+	.	.	+	.	.	+	.	+	.	.	+	.	.	+	+	+	+
Campanula trachelium	.	.	.	+	.	.	+	+	.	.	.	.	+	.	.	.	.	.	.	.	.	.	+	+	.	+	+	+
Robinia pseudoacacia	.	.	.	.	.	.	+	.	.	.	1	1	.	.	.	.	+	.	r	2	.	1	2	.	.	.	2	.
Ranunculus lanuginosus	+	.	+	.	.	.	+	.	.	.	.	.	.	.	+	+	.	.	.	.	.	+	.	.	.	1	1	+
Eupatorium cannabinum	.	.	+	.	.	.	+	.	+	+	+	+	.	.	.	.	.	.	.	.	.	.	1	1	.	+	.	.
Euonymus europaeus	.	+	.	+	+	.	.	2	.	+	.	.	.	.	.	.	.	.	.	+	+	+	+	.	.	.	.	.
Dryopteris filix-mas	+	.	.	+	+	+	.	.	.	.	+	.	.	.	.	.	.	.	r	1	.	.	.	.	+	.	+	.
Lamium galeobdolon subsp. flavidum	1	1	1	.	1	.	+	+	.	.	.	.	.	+	2	.	.	.	+	.	.	.	.	.	.	.	.	.
Prunus avium	.	.	.	.	.	.	.	.	.	+	.	+	+	1	.	1	+	.	.	.	.	.	.	+	+	.	.	.
Emerus major	.	+	.	+	.	.	.	.	.	.	+	.	+	+	.	.	.	.	.	.	.	+	.	+	.	.	.	.
Galium aparine	.	.	.	.	.	.	.	.	.	+	1	.	.	+	+	.	.	+	.	.	.	.	.	.	+	+	.	.
Sanicula europaea	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	2	+	.	.	.	.	.	+	.	.	+	+	+
Acer pseudoplatanus	.	.	.	.	.	+	.	.	.	2	.	.	+	+	r	+	+	.	.	.	.	.	.	.	.	.	.	.
Solidago virgaurea	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	+	+	.	r	.	.	+	.	+	.	.	+	.
Viola riviniana	+	.	.	+	+	+	1	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.
Tussilago farfara	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	+	.	.	.	.	1	1	.	2	1	+
Pulmonaria hirta	.	.	.	.	.	.	.	.	1	+	+	.	.	.	.	+	.	.	.	.	.	.	+	.	+	.	.	.
Daphne laureola	.	.	.	.	+	.	.	.	.	.	.	+	+	.	.	.	+	.	.	r	.	.	.	.	.	.	.	+
Helleborus viridis subsp. bocconei	.	.	.	.	.	.	.	.	1	.	.	.	.	.	+	+	+	.	r	.	+	.	.	.	.	.	.	.
Viola alba subsp. dehnhardtii	.	.	.	.	.	.	.	.	1	+	.	.	.	.	1	1	1	.	.	r	.	.	.	.	.	.	.	.
Equisetum arvense	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	+	+	.	.	.	r	.	+	.	.	+	.	.
Arum italicum	+	.	.	.	.	.	.	.	+	.	.	.	.	1	+	+	.	.	.	r	.	.	.	.	.	.	.	.
Carex sylvatica	.	.	.	.	.	.	.	.	.	1	r	.	.	.	.	+	.	.	.	.	.	1	1	.	+	.	.	.
Carpinus betulus	.	2	.	.	.	.	.	.	.	.	.	.	.	1	.	1	.	.	.	1	.	.	.	.	.	+	+	.
Castanea sativa	.	.	.	.	.	2	.	.	.	.	+	.	.	.	.	.	.	1	.	r	2	.	.	.	1	.	.	.
Arctium lappa	+	.	.	.	.	r	.	.	.	.	.	.	+	.	+	+	.	.	.	.	.	r	.	.	.	.	.	.
Dactylis glomerata	.	.	.	.	.	.	.	.	.	.	+	.	.	+	.	.	.	.	.	.	.	+	.	+	.	+	.	.
Athyrium filix-femina	1	.	.	1	1	1	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.
Salvia glutinosa	.	.	.	.	+	.	.	.	.	.	+	.	.	.	.	.	.	.	.	+	.	+	.	.	2	.	.	.
Cornus mas	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	2	.	+	1	.
Lonicera etrusca	.	+	+	.	+	.	.	.	.	.	.	.	.	.	1	.	+	.	.	.	.	.	.	.	.	.	.	.
Rubia peregrina	+	.	.	.	.	.	.	.	.	+	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+
Festuca heterophylla	.	.	.	.	.	.	.	.	.	.	.	+	.	1	.	.	.	.	.	.	.	+	.	.	+	.	.	.
Chaerophyllum hirsutum (incl. C. calabrum)	.	.	.	.	.	.	.	.	.	.	.	+	+	+	.	.	+	.	.	.	.	.	.	.	.	.	.	.
Rosa canina	.	.	.	.	.	.	.	.	.	.	.	.	+	+	.	+	+	.	.	.	.	.	.	.	.	.	.	.
Cardamine bulbifera	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	+	.	.	.	2	.	+	.
Rosa arvensis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	+	+	+
Ruscus aculeatus	.	1	+	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Mentha aquatica	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	+	+	.	.	.	.
Ulmus minor	.	.	+	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.
Rubus hirtus	.	.	.	.	.	.	1	2	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.
Ficaria verna	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	+	+	.
Ligustrum vulgare	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	+	.	+
Hypericum androsaemum	+	.	.	.	.	.	+	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Anemonoides nemorosa	.	.	.	+	.	.	.	.	r	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Prunus spinosa subsp. spinosa	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	+	.	.	.	.	.	.	.	.	+	.	.	.
Galium album	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	+	.	+	.	.
Lolium giganteum	.	.	.	.	.	.	.	.	.	.	.	+	+	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.
Bryonia dioica	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	+	+	.	.	.	.	.	.	.
Moehringia trinervia	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	1	.	r	.	.	.	.	.	.	.	.
Laurus nobilis	.	1	+	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Potentilla micrantha	.	.	.	.	.	.	.	.	.	.	.	.	+	1	.	.	.	.	.	.	.	.	.	.	+	.	.	.
Quercus cerris	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	1	1	.	.	.	.
Asplenium trichomanes subsp. quadrivalens	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	r	.	.	.	.	.	.	.
Pteridium aquilinum subsp. aquilinum	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.
Equisetum telmateia	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	+	.	.	.
Ranunculus repens	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.
Poa sylvicola	.	.	.	.	.	.	.	.	.	+	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Scrophularia nodosa	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.
Brachypodium rupestre	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	2	.	.	.	.
Asplenium scolopendrium subsp. scolopendrium	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.	.	.	.	.	.	.
Fragaria vesca subsp. vesca	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	+	.	.	.	.	.	.
Geranium purpureum	.	.	.	.	.	.	.	.	.	+	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Heracleum sibiricum subsp. ternatum	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.	.	r	.	.	.	.	.	.	.
Impatiens parviflora	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	r	.	.	.	.	.	.	.
Cardamine pratensis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	r	.	.	.	.	.	.	.	.
Senecio ovatus	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	1
Cardamine heptaphylla	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Saxifraga rotundifolia	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.
Ficus carica	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.
Cyclamen repandum subsp. repandum	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.
Rumex sanguineus	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.
Stellaria media subsp. media	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Lonicera caprifolium	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Poa trivialis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.	.
Arisarum proboscideum	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.
Mercurialis perennis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+
Agrostis stolonifera	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.
Fagus sylvatica subsp. sylvatica	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	2	.	.	.
Euphorbia amygdaloides	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.
Poa nemoralis	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.
Juglans regia	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.
Physospermum cornubiense	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.	.	.	.	.	.	.	.	.	.
Parietaria officinalis	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Cyclamen hederifolium	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.
Cruciata glabra	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Acer opalus subsp. obtusatum	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Bromopsis ramosa	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.
Rumex conglomeratus	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Ailanthus altissima	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	2	.	.	.	.	.	.	.	.
Chelidonium majus	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.
Selaginella denticulata	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Arisarum vulgare subsp. vulgare	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Cardamine chelidonia	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	2	.	.	.
Plantago major	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.
Pulicaria dysenterica	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.
Sedum cepaea	.	.	.	.	.	.	.	.	.	.	+	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.
Veronica urticifolia	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	r	.	.	.	.	.	.	.
Adoxa moschatellina subsp. moschatellina	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	.	1	.	.	.

, hoc loco.

Diagnostic species: Geranium nodosum, Pulmonaria hirta, Aegopodium podagraria, Campanula trachelium, Cornus sanguinea, Dactylis glomerata, Daphne laureola, Emerus major, Euphorbia dulcis, Helleborus viridis subsp. bocconei, Ostrya carpinifolia, Robinia pseudoacacia.

Constant species: Acer campestre, Alnus glutinosa, Brachypodium sylvaticum, Carex pendula, Circaea lutetiana, Clematis vitalba, Corylus avellana, Fraxinus ornus, Hedera helix subsp. helix, Melica uniflora, Mycelis muralis, Sambucus nigra.

Dominant species: Alnus glutinosa.

Structure and ecology: This riparian vegetation is very close to the previous communities of Cluster 11, and also occurring on similar geological substrates. Clusters 11 and 12 also share several diagnostic and constant species (Geranium nodosum, Circaea lutetiana, Euphorbia dulcis, Melica uniflora, etc.), but the relevés of Cluster 12 are less markedly mesophilous, because they are generally present at lower altitudes, between 150 and 600 m a.s.l. Floristically, the herbaceous layer has lost many species of beech woods, which have been replaced by lower-altitude entities (e.g., Saxifraga rotundifolia is non more present, while Petasites albus has been replaced by Petasites hybridus). The tree layer is dominated by Alnus glutinosa with low cover values of other wood species, such as Acer campestre and Ostrya carpinifolia, sometimes also with the invasive Robinia pseudacacia. The dominated tree and shrub layers are characterized by Sambucus nigra and Corylus avellana, as in Cluster 11. For all the above-mentioned reasons, we propose treating the relevés of Cluster 12 as a subassociation of the Geranio nodosi-Alnetum glutinosae, named cornetosum sanguineae.

Distribution: Tuscany. Lucca, Pistoia, Prato, Siena and Arezzo Apennines.

Landscape context: The subassociation is in catenal contact with mesophilous and thermophilous deciduous mixed oak woods and chestnut woods of the Quercetalia pubescenti-petraeae.

• 13. Hyperico hircini-Alnetum glutinosae Gafta and Pedrotti 1996 (Cluster 13)

Syn.: Circaeo lutetianae-Alnetum glutinosae (Blasi and Frondoni 1996)

Holotypus: Rel. 1, [55] (pp. 414–415)

Diagnostic species: Amorpha fruticosa, Bidens frondosa, Carex riparia, Limniris pseudacorus, Lythrum salicaria, Salix alba, Tommasinia altissima.

Constant species: Alnus glutinosa, Brachypodium sylvaticum, Carex pendula, Clematis vitalba, Eupatorium cannabinum, Hedera helix subsp. helix, Rubus ulmifolius.

Dominant species: Alnus glutinosa, Brachypodium sylvaticum.

Characteristic species (according to the literature): Hypericum hircinum subsp. majus

Structure and ecology: Riparian thermophylous wood vegetation dominated by A. glutinosa, associated with Salix alba and S. pedicellata [55]. The shrubby and lianose layer is well represented with Ficus carica, Ulmus minor, Sambucus nigra, Hedera helix, Clematis vitalba, Vitis vinifera subsp. sylvestris, Solanum dulcamara. Some nemoral and hygrophilous species make up the herbaceous layer, including Carex pendula, C. remota, Rumex sanguineus, Arum italicum. These vegetation woods grow along perennial waterways that flow in the coastal plains or in wide, slightly sloping valleys of the hilly belt, from sea level up to about 600 m. They are widespread in areas characterized by Mediterranean pluseasonal oceanic bioclimate, thermo-Mediterranean thermotype and subhumid–humid ombrotype.

Distribution: Calabria, Latium, Abruzzo, Umbria, Tuscany, Emilia Romagna.

Landscape context: This riparian wood potentially makes catenal contact with Quercus virgiliana, thermophilous oak woods of the Quercetea ilicis class, or with the secondary communities, such as scrub vegetation of Rhamno-Prunetea.

Notes: the type described by Gafta and Pedrotti [55] for Calabria is grouped with the plant communities of Tuscany and Latium, previously indicated as Circaeo lutetianae-Alnetum glutinosae.

• 14. Lamio orvalae-Alnetum glutinosae Dakskobler 2016 (Cluster 14)

Holotypus: Rel. 9, Tab.8 [116].

Diagnostic species: Filipendula ulmaria, Fraxinus excelsior subsp. excelsior, Lamium galeobdolon subsp. flavidum, Lamium orvala, Potentilla indica, Quercus robur, Rubus caesius, Valeriana dioica, Virburnum opulus, Frangula alnus subsp. alnus, Glechoma hederacea, Ligustrum vulgare, Polygonatum multiflorum, Prunus avium.

Constant species: Alnus glutinosa, Carex pendula, Carex remota, Cornus sanguinea, Corylus avellana, Geum urbanum, Hedera helix subsp. helix, Sambucus nigra.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Lamium orvala, Primula vulgaris, Cerastium sylvaticum, Galanthus nivalis, Loncomelos pyrenaicus [66]; Alnus glutinosa, Lamium orvala, Ornithogalum pyrenaicum and Galanthus nivalis, Scilla bifolia, Allium ursinum, Cardamine bulbifera, Crocus vernus subsp. vernus [116].

Structure and ecology: Riparian woods occurring along the small rivers of the hilly and lowland belt of north-eastern Italy. This vegetation grows on medium-evolved and brownified, neutral-alkaline, clayey or fluvisol soils, often on mixed mother rock, flysch, marl and carbonates. The tree layer is characterized by A. glutinosa, Acer campestre, Prunus avium, Quercus robur, Salix alba, Populus nigra, while very rare are Carpinus betulus, Acer pseudoplatanus, Ulmus minor. The shrub layer is mainly characterized by Rubus caesius, together with Cornus sanguinea, Corylus avellana, Viburnum opulus, Ligustrum vulgare, Sambucus nigra, Crataegus monogyna, etc. The herbaceous layer consists of large tufts of Carex pendula and Carex remota, together with Geum urbanum, Athyrium filix-femina, Lamium galeobdolon subsp. flavidum, Primula vulgaris, Dryopteris filix-mas.

Distribution: north-eastern Italy (Friuli Venezia Giulia, Veneto, Lombardy).

Landscape context: The association is in catenal contact with Lamio orvalae-Ulmetum and with neutral acidophilous oak forests of medium and high slopes (Carici umbrosae-Quercetum petraeae, Seslerio autumnalis-Quercetum pubescentis). In the lower plain, the contacts are with the hygrophilous hedges (Frangulo-Viburnetum opuli) and with herbaceous cenoses representing secondary stages of the plain wood (Asparago-Quercetum roboris), such as Poo-Lolietum multiflori and Plantagini-Molinietum caeruleae [66].

Notes: Lamio orvalae-Alnetum glutinosae, described by Dakskobler [116] for south-western Slovenia, is classified in the Fagetalia sylvaticae. Subsequently, Lamio orvalae-Alnetum glutinosae is reported by Poldini and Sburlino [66] for the first time in north-eastern Italy. According to Poldini and Sburlino [66], due to its azonality character, Lamio-Alnetum glutinosae is to be included in the Alnion incanae alliance and Alno-Fraxinetalia excelsioris order (Alno-Populetea), the latter order grouping the azonal riparian communities of central Europe. Our results include Lamio orvalae-Alnetum glutinosae in the Ligustro vulgaris-Alnion glutinosae alliance, where the association finds a chorological correspondence with the diagnosis of the alliance described by Poldini et al. [16] for northern and central Italy. In our opinion, this vegetation should be studied more in depth, in order to correctly classify it.

• 15. Polysticho setiferi-Alnetum glutinosae Brullo, Scelsi, Spampinato 2001 (Cluster 15, Figure 7)

Holotypus: Rel. 1, Tab. 29 [61].

Diagnostic species: Dactylorhiza maculata subsp. saccifera, Geranium versicolor, Poa trivialis, Rubus canescens, Stachys sylvatica, Arctium minus, Athyrium filix-femina.

Constant species: Alnus glutinosa, Brachypodium sylvaticum subsp. sylvaticum, Carex remota, Geranium robertianum, Lamium flexuosum, Mycelis muralis, Sambucus nigra, Urtica dioica.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Polystichum setiferum.

Structure and ecology: Riparian woods with a clear dominance of Alnus glutinosa. The shrub layer is poorly represented with Ilex aquifolium, Sambucus nigra and Salix caprea. Various hygrophilous and calcifugous ferns live in the herbaceous layer, among which in particular Polystichum setiferum, Dryopteris affinis, Athyrium filix-femina, which make the association different. This plant community grows along watercourses that flow in narrow valleys and ravines of the mountain and submontane belt, between 500 and 1100, characterized by a wetter and cooler mesoclimate than the surrounding macroclimatic conditions that fall within the meso or supra-Mediterranean humid or hyperhumid bioclimatic belt. It occurs in the Mediterranean-mountain areas geologically characterized by metamorphic rock or granites.

Distribution: Serre Calabre, Sila, North and Western slope of Aspromonte (Calabria) [117,118], Cilento (Campania).

Landscape context: This wood normally makes catenal contact with mixed meso-thermophilous deciduous forests growing on the slopes of the valleys, and referrable to the Tilio-Ostryon carpinifoliae Brullo, Scelsi and Spampinato 2001 or Pino-Quercion congestae Brullo Scelsi, Siracusa and Spampinato 1999, both alliance endemic of southern Italy [119].

Notes: Based on our analysis, the Campania findings attributed by Rosati et al. [58] to Euphorbio corallioides-Alnetum glutinosae are also to be included in the Polysticho setiferi-Alnetum glutinosae.

• 16. Euphorbio corallioides-Alnetum glutinosae Brullo and Furnari in Barbagallo et al. 1982 (Cluster 16, Figure 7)

Holotypus: Rel. 1, Tab. 1 [59].

Diagnostic species: Ajuga reptans, Aquilegia vulgaris, Arctium lappa, Arisarum proboscideum, Chaerophyllum hirsutum (incl. C. calabrum), Cirsium creticum subsp. triumfettii, Clinopodium vulgare, Crepis leontodontoides, Cruciata laevipes, Dactylorhiza maculata, Dryopteris filix-mas, Euphorbia corallioides, Euphorbia meuselii, Geranium lucidum, Geranium versicolor, Holcus mollis, Hypericum perforatum, Impatiens noli-tangere, Lamium galeobdolon subsp. montanum, Lapsana communis, Lysimachia nummularia, Mentha longifolia, Poa nemoralis, Prunella vulgaris subsp. vulgaris, Rubus idaeus subsp. idaeus, Rumex acetosa, Rumex sanguineus, Scrophularia scopolii, Solanum dulcamara, Stachys sylvatica, Thalictrum aquilegiifolium subsp. aquilegiifoli, Thalictrum lucidum, Thalictrum simplex subsp. simplex, Trifolium repens, Veronica montana, Fagus sylvatica subsp. sylvatica, Galium aparine, Lamium flexuosum, Polygonatum multiflorum, Pteridium aquilinum subsp. aquilinum, Symphytum tuberosum subsp. angustifolium.

Constant species: Alnus glutinosa, Brachypodium sylvaticum, Carex pendula, Carex remota, Sambucus nigra, Urtica dioica.

Dominant species: Alnus glutinosa.

Characteristic species (according to the literature): Arisarum proboscideum, Aquilegia vulgaris, Euphorbia corallioides, Thalictrum simplex subsp. simplex.

Structure and ecology: Riparian wood with a canopy dominated by A. glutinosa accompanied to few other tree species as Populus nigra. A rich contingent of hygrophilous nemoral species make up the herbaceous layer, such as Athyrium filix-femina, Carex remota, Chaerophyllum hirsutum (incl. C. calabrum), Thalictrum aquilegiifolium and some endemic or subendemic species from southern Italy, such as Euphorbia corallioides, Arisarum proboscideum.

The association occurs along the rivers of the mountain belt, between 900 and 1300, generally on flat or slightly steep alluvial soils of a siliceous nature originating from metamorphytes or from granites and granodiorites, in areas with an oceanic temperate bioclimate with thermotype between upper mesotemperate and lower supratemperate, and upper subhumid ombrotype.

Distribution: Mountain range of Calabria. Described for the Serre Calabre plateau [59], it is also widespread on the Sila plateau [60] while it becomes rarer in Aspromonte [61,118].

Landscape context: These alder woods occur along rivers that flow in areas potentially occupied by beech forests of the Geranio versicoloris-Fagion sylvaticae Gentile 1970 but, rather than with beech woods they make contacts with secondary formations of the dynamic series, such as acidophilous shrublands of the class Cytisetea scopario-striati Rivas-Martínez 1975 or Pteridium aquilinum stands, as on the Sila and Serre Calabre highlands cultivated in the past and then abandoned and used as pasture.

Notes: The localization of this community in the oceanic temperate bioclimate affects the rich contingent of Querco-Fagetea nemoral species, such as Brachypodium sylvaticum, Geranium versicolor, Poa nemoralis, and Euphorbia meuselii. In Sila highlands, alder woods form a gallery forest that closes above the river, favouring a constant shadow thanks to which can be established very rare hygrophilous nemoral sciaphilous plant communities in direct contact with water that hosts species of great phytogeographical interest, such as Rhynchocorys elephas, Chrysosplenium dubium and the endemic Cryptotaenia thomasii.

• 17. Asperulo taurinae-Alnetum glutinosaeass. nov. hoc loco (Cluster 17)

Syn.: Euphorbio corallioides-Alnetum glutinosae sensu Rosati et al. (2005) non Brullo and Furnari in Barbagallo et al. 1982

Holotypus: Rel. 11, Tab. 8 [58].

Diagnostic species: Alnus cordata, Anemone apennina, Aremonia agrimonoides subsp. agrimonoides, Arisarum proboscideum, Asperula taurina subsp. taurina, Geranium versicolor, Juglans regia, Lamium flexuosum, Lysimachia nummularia, Rubus hirtus, Salvia glutinosa, Symphytum bulbosum, Circaea lutetiana, Lamium galeobdolon subsp. montanum, Melica uniflora, Polystichum setiferum, Ranunculus lanuginosus, Sanicula europaea, Scutellaria columnae subsp. gussonei, Vinca major.

Constant species: Alnus glutinosa, Arum italicum, Athyrium filix-femina, Brachypodium sylvaticum subsp. sylvaticum, Carex pendula, Clematis vitalba, Dioscorea communis, Geranium robertianum, Mycelis muralis, Rubus ulmifolius, Viola reichenbachiana.

Dominant species: Alnus glutinosa.

Structure and ecology: Riparian woods growing along the high course of the streams engraved in the slopes of the arenaceous-conglomerate reliefs of Mt. Sacro, between 500 and 1200 m a.s.l.; the area is characterized by mesotemperate to the lower supratemperate bioclimate, humid to sub-humid level. Occasionally, in particular geomorphological areas, it is possible to find these woods even at much lower altitudes (250 m a.s.l.). The tree layer, dominated by A. glutinosa, covers between 60 and 90%. The shrub layer, with average cover of about 60%, consists of Rubus hirtus, R. ulmifolius, Sambucus nigra, Clematis vitalba, Hedera helix, Dioscorea communis. The herbaceous layer is rich in hygrophilous species, such as Carex pendula, C. remota, Circea lutetiana, Lysimachia nemorum; also several mesophilous species are frequent, such as Stachys sylvatica, Salvia glutinosa, Scrophularia scopolii, Arisarum proboscideum, Asperula taurina, Geranium versicolor, Lamium flexuosum, Melica uniflora, Ranunculus lanuginosus, Sanicula europaea. Numerous nitrophilous species also occur: Urtica dioica, Galium aparine, Arum italicum, Ranunculus repens. Some ferns find in these environments their optimum: Athyrium filix-femina, Dryopteris filix-mas and Polysticum setiferum. The communities observed in the Cilento area show a strong ecological, coenological and biogeographic affinity with the association Euphorbio corallioides-Alnetum glutinosae described for the Serre Calabre [59]. Nevertheless, most of the species reported as characteristics of the association (Euphorbia corallioides, Chaerophyllum hirsutum var. calabricum, Arisarum proboscideum, Thalictrum morisonii subsp. mediterraneum, Thalictrum simplex subsp. simplex, Aquilegia vulgaris) have a local significance; thus, the Euphorbio corallioides-Alnetum glutinosae has to be considered as limited to different parts of the Calabria region (Serre, Aspromonte, Sila) at elevation between 900 and 1300 m a.s.l., within the climatic belt of Geranio versicoloris-Fagion [60]. Among the characteristic species of Euphorbio corallioides-Alnetum glutinosae, only Arisarum proboscideum and Aquilegia vulgaris are present in the communities analyzed in the Cilento. For this reason, we propose a new association with the name Asperulo taurinae-Alnetum glutinosae. From the syntaxonomic point of view, the association is to be referred to the Alnion incanae for the presence and abundance in these communities of a large contingent, such as Stachys sylvatica, Circaea lutetiana, Carex remota, Carex pendula, Symphytum tuberosum, and Rumex sanguineus.

Distribution: Cilento, Campania [58].

Landscape context: This riparian wood potentially makes catenal contact with beech forests of the Geranio versicoloris-Fagion sylvaticae Gentile 1970. In altered environments, they make contacts with secondary formations, such as acidophilous shrublands of the class Cytisetea scopario-striati Rivas-Martínez 1975.

Notes: Gafta and Pedrotti [55] on the basis of the presence of some differential species (Arisarum proboscideum, Hypericum hircinum, Geranium versicolor) refer the Euphorbio-Alnetum glutinosae to the Hyperico androsaemi-Alnenion glutinosae.

• 18. Angelico sylvestris-Alnetum glutinosae Brullo and Spampinato 1997 (Cluster 18, Figure 7)

Holotypus: Rel. 12, Tab. 2 [60].

Diagnostic species: Angelica sylvestris subsp. sylvestris, Convolvulus silvaticus, Ranunculus neapolitanus, Rumex sanguineus, Salix alba, Salix brutia, Solanum dulcamara, Valerianella locusta, Veronica scutellata, Vinca minor, Viola alba subsp. dehnhardtii, Chaerophyllum temulum, Clematis viticella, Helosciadium nodiflorum, Poa trivialis, Populus alba.

Constant species: Alnus glutinosa, Arum italicum, Brachypodium sylvaticum, Carex pendula, Clematis vitalba, Hedera helix subsp. helix, Rubus ulmifolius, Sambucus nigra, Stachys sylvatica, Urtica dioica.

Dominant species: Alnus glutinosa, Angelica sylvestris, Salix alba.

Characteristic species (according to the literature): Angelica sylvestris.

Structure and ecology: Riparian woods dominated by A. glutinosa associated with other hygrophilous trees, such as Populus alba, P. nigra and Salix alba. The shrubby and lianose layer is well represented with Sambucus nigra, Cornus sanguinea, Hedera helix, Clematis vitalba, Solanum dulcamara. A rich group of nemoral and hygrophilous species makes up the herbaceous layer, including Angelica sylvestris, Carex pendula, C. remota, Rumex sanguineus, and Stachys sylvatica. These alder woods grow along perennial waterways that flow in the coastal plains or in wide, slightly sloping valleys of the hilly belt, from sea level up to about 600 m. They are widespread in areas characterized by Mediterranean pluseasonal oceanic bioclimate, thermo or meso-Mediterranean thermotype and subhumid–humid ombrotype. The alluvial soils are loamy or sandy, rich in organic matter, normally flooded during the winter with high edaphic humidity even in summer. The high presence of Urtica dioica, Chaerophyllum temulum and Stachys sylvatica reveals a substrate rich in nutrients.

Distribution: Central-northern Calabria [117].

Landscape context: This riparian woods potentially make catenal contact with Quercus virgiliana, thermophilous oak woods of the Quercetea ilicis class, or with the secondary formations of the dynamic series, such as scrub communities located on non-alluvial soils outside the river floodplain. More frequently, they are flanked by cultivated or uncultivated lands.

In relation to variations in river dynamics, this association constitutes a gallery wood in direct contact with the lower bed of the watercourse or is separated from it by a band of shrub willows of the Salicetea purpureae class. In this case, species such as Salix purpurea subsp. lambertiana, S. brutia can be found in the shrub layer.

Notes: In the lowland areas with a more prolonged period of flooding, such as at the mouths of the main rivers, occurs the particular subassociation of the Angelico sylvestris-Alnetum glutinosae iridetosum pseudacori, differentiated by Clematis rigoi (endemic of southern Italy) and Limniris pseudacorus, both species linked to loamy soils with high groundwater. This subassociation makes catenal contact with Populus alba lowland woods of the Clematido viticellae-Populetum albae [60,120].

4. Conclusions

The present paper provides a comprehensive and exhaustive framework of the A. glutinosa riparian woodlands diversity in the central Mediterranean area. Overall, a total of 18 A. glutinosa-riparian wood communities were distinguished for Italy and Tyrrhenian islands, of which two new associations and one new subassassociation are described within the Ligustro vulgaris-Alnion glutinosae (Geranio nodosi-Alnetum glutinosae, Geranio nodosi-Alnetum glutinosae cornetosum sanguineae, Asperulo taurinae-Alnetum glutinosae). The alder forests in Italy and Corsica are classified into the Populetalia albae order (Alno glutinosae-Populetea albae class). This order, with Mediterranean gravitation, includes two alliances. The first, Osmundo-Alnion, with west-Mediterranean and Tyrrhenian Italy distribution, is split into two different geographical groups: Hyperico hircine-Alnenion glutinosae that includes the thermophilous communities with a circumtyrrhenian distribution (Sardinia, Corsica, north-aestern Sicily, Tyrrhenian coasts of the Italian peninsula) and Struthioptero-Alnenion glutinosae suballiance, that includes the thermo-mesophilous plant communities of central Italy, up to the Sardinian and Corsican mountains. The second alliance, Ligustro vulgaris-Alnion glutinosae, includes the riparian meso-thermophilous communities of the northern and central and southern peninsula. This last alliance shows two geographic variants at the national level, which should be better investigated: the first includes the more mesophilous communities with the northern Italy distribution, while the second includes the southernmost mesophilous communities.