Advancing Knowledge of Wetland Vegetation for Plant Diversity Conservation: The Case of Small Lakes, Ponds, and Pools in Maremma (Southern Tuscany, Central Italy)

Abstract

Wetlands are among the world’s valuable ecosystems for biodiversity conservation, but they are also among the most threatened habitats, heavily impacted by human pressures and threats. The Mediterranean basin features numerous small lakes, ponds, and pools, whose number and quality are decreasing at an alarming rate, and whose biodiversity is often little or not at all known. As a better knowledge of the biotic components of these minor water bodies is necessary, with this aim a phytosociological survey campaign was carried out in southern Tuscany (central Italy), an area where little information is available on the vegetation of aquatic and palustrine biotopes. Numerous previously unknown water bodies were located and surveyed in this work, while others already known were resurveyed. These investigations allowed us to identify 28 plant communities which can be classified into seven syntaxonomic classes. A new subassociation (Ranunculo ophioglossifolii-Callitrichetum stagnalis subass. ranunculetosum peltati) is described. The identification of the site-associated Natura2000 habitats led to the recognition of five habitats of conservation interest at the national and European level. The results of these investigations will improve the knowledge of the flora and vegetation of these small but valuable natural areas, providing a basis for their conservation.

1. Introduction

Wetlands are among the most valuable ecosystems on the planet, providing a wide range of ecological services [1,2,3,4] and being crucial for the conservation of biodiversity [1,5,6]. However, wetlands are among the most threatened habitats in the world, severely affected by human pressures and threats, such as agricultural and urban land transformation, overexploitation, water pollution, flow alteration, habitat destruction or degradation, and invasion by non-native species [1,5,7,8,9]. This worrying global trend has increased rapidly in recent years, even for wetlands within protected areas [10,11,12]. It is therefore not surprising that freshwater ecosystems include many threatened habitats with an unfavorable conservation status, also in Europe [13] and in Italy [14,15,16,17,18].

In addition to large wetlands, for which much information is often available [19,20,21], the Mediterranean basin also features numerous small lakes, ponds, and pools, both in the mountains and in the lowlands, whose biodiversity is often little or not at all known [21,22]. Especially at relatively low elevations, many of these freshwater ecosystems can be partially or completely artificial in origin, related to anthropogenic activities, but still of great importance for plant diversity [7,23,24] and conservation [25,26,27]. In the Mediterranean basin, small water bodies, permanent or more or less temporary, are generally widespread and provide important ecosystem services, but their quantity and quality are decreasing at an alarming rate [19,28], and many are partially or completely unknown.

Therefore, a better knowledge of the biotic components of these minor water bodies is necessary for their conservation, and many scholars recommend carrying out inventories of wetland biodiversity throughout the Mediterranean, particularly for neglected wetland types [21,22].

For these reasons and with this aim, a vegetation survey campaign was carried out in southern Tuscany (central Italy) and in particular in Maremma (Figure 1), an area where the vegetation information on aquatic and palustrine communities is scarce: To our knowledge, only two works [29,30] have studied the plant communities of some small inland water bodies in this area. Few others have taken into account large inland lakes or riverbeds [31,32]. A few more have considered coastal wetlands [33,34], often with a predominant zoological or ecosystemic approach [35,36]. Numerous previously unknown water bodies have been located and surveyed in this work, while others have been revisited after several years since the first survey. The results of these investigations are the object of this contribution.

2. Materials and Methods

2.1. Study Area

The 19 study sites are located in the province of Grosseto (42.7705° N, 11.1121° E), Figure 1, the southernmost and largest one in Tuscany, Italy. A general description of the main environmental characteristics and phytogeographical sectors of this area is given by Selvi [37,38]. Most of the sites are located in the northern hill-planitial sector, while only two (Lagaccioli, L1 and L2 in Figure 1) belong to the southern hill-planitial sector. All wetland site names, abbreviations, geographical details, and information about inclusion in protected areas are given in in Supplementary Material Information File S1. Some images of the wetlands are provided in Supplementary Material Figure S1.

2.2. Climate and Bioclimate

With an average annual rainfall of 720–800, approximately 3 months of drought, and an average annual temperature of 14–14.5 °C, the climate is typically meso-Mediterranean. According to the classification of Thornthwaite & Mather [39], the climate belongs to the type “second mesothermic, suboceanic (B’2b’4)”, and varies from “humid to subhumid (C2 s)” for the northern sites and from “subhumid to subarid (C1w2)” for the southern sites. Regarding the bioclimate, according to Pesaresi et al. [40], the study area has a Pluviseasonal oceanic Mediterranean bioclimate. Only the northern sites are close to the border with the oceanic submediterranean Temperate bioclimate. Following the Italian ecoregion approach [41], all the sites are located in the Thyrrenian Province of the Mediterranean Division, specifically in the Maremma Subsection (2B1b). Again, some of the northern sites are near the border with the Apennine Province of the Temperate Division, specifically near the Tuscan Basin Subsection (1C1b).

2.3. Geological Outline

The sites of the northern sector are mainly located around Monte Leoni (616 m a.s.l.), the highest elevation of a vast hill system mainly oriented along a NE–SW direction and covering an area of ca. 120 km² between the Ombrone and the Bruna rivers, to the east and the west, respectively. The geological backbone of the area is formed by the so-called “Verrucano” formation, an assemblage of crystalline siliceous rocks of quartzitic-anagenetic type dating back to the Upper Triassic [42,43,44,45]. The seven sites LDP, LMU, LTC, LPM, POM, SDP, and LVN (see in Supplementary Material Information File S1 for the meaning of abbreviations and other geographical information) lie in a vast low-elevation plateau (150–200 m a.s.l.) extending at the base of the northern side of Mt. Leoni. This plateau is composed of fluvio-lacustrine sands and loose conglomeratic material originated in a continental environment by the erosion of the siliceous rocks from the surrounding hill slopes and deposited in thick layers during the Pleistocene [46]. The area includes small springs, water veins, and natural pools, some of which were transformed into small semi-permanent ponds (POM, LDP, LMU, LVN) or permanent lakes (LTC, LPM), to provide water for the livestock kept by the local population in the area since at least the 18th century. The LPR site is a shallow seasonal pond of natural origin located at the western foot of the Mt. Leoni area, on sandy-silty soil. The FV site is similar, but lies on acid-effusive rocks of the rhyolitic type formed during local volcanic phases of the Pliocene. This site is included in a dense cork oak forest and was not used for livestock watering. The PL site is a seasonal artificial pond created in the plain of river Bruna at the NW of Mt. Leoni, with alluvial soil of sandy-silty texture, used for a long time for cattle watering.

The ponds in the south-western part of the study area (LE, LCE, PE, AUN) are mainly artificial in origin and are located in the southern sector of the Mt. Leoni hill complex, also consisting of the quartzitic Verrucano formation described above. The south-eastern ponds PSR, LC, and PSB are also of artificial origin, but located in a hilly area dominated by a mid-Eocene-Paleocene clayey-calcareous formation [43].

The two sites in the southern sector are the Lagaccioli lakes (L1 and L2), located in a heterogeneous geological area with limestone, shale, clay, and sandstone, together with pebbles and mud of alluvial and lacustrine origin [29,45]. Their formation is thought to be of karstic origin [47].

2.4. Data Set and Data Analysis

The dataset is composed of 88 original relevés carried out in plant communities dominated by aquatic and palustrine species. The data were collected in the spring 2024 (April–June) using the classical phytosociological method [48,49] and its updates [50,51,52,53]. After transforming the original Braun–Blanquet cover-abundance scale into the Van der Maarel ordinal scale [54], aquatic coenoses were separated from palustrine ones, based on the growth forms [55] of the dominant species. The two resulting matrices were then analysed through a cluster analysis in the R environment [56], using the chord distance of the function vegdist of ‘vegan’ package [57] and the median linkage of the function hclust of ‘stats’ package [56].

Plant species names follow Portal to the Flora of Italy [58] based on Bartolucci et al. [59], while the syntaxonomic nomenclature of classes, orders, and alliances mainly follows “Vegetation of Europe” by Mucina et al. [60], and Italian Vegetation Prodrome [61]. The syntaxonomical nomenclature is in accordance with the 4th edition of the ICPN [62].

3. Results and Discussions

The dendrograms resulting from the cluster analysis are shown in Figure 2 and Figure 3, where the correspondence between relevés and plant communities is given. The classification provided by the cluster analysis was followed entirely for the aquatic communities and 94% for the palustrine ones; as is inherent in the phytosociological procedure, more importance was given to the floristic composition, both in terms of dominance and bioindication, to discriminate phytocoenoses. An example of this is the communities dominated by the Glyceria fluitans, composed of two relevés, all rather poor in floristic terms, but with no accompanying species in common. In this case, the cluster analysis separates these two relevés, which on the contrary should be classified in the same plant community type on the basis of species dominance and ecology. The analysis allowed us to identify 28 different plant community types which can be classified syntaxonomically into seven classes: Charetea intermediae, Lemnetea, Potamogetonetea, Isoëto-Juncetea, Littorelletea uniflorae, Phragmito-Magnocaricetea, and Molinio-Arrhenatheretea. Each community type is described and commented on in the following paragraphs. A comprehensive syntaxonomic scheme is reported in Appendix A.

3.1. Aquatic Plant Communities

Nitelletum hyalinae Corillion 1957 (Supplementary Material Table S1, rel. 1)

Several algal species of Characeae were found in the wetlands studied, mostly in mosaic with aquatic vascular plant communities and often forming a more or less dense lower layer in the coenoses of the Potametea class. In some cases, the collected specimens lacked the diagnostic characters necessary for the identification at the species level, while in other cases it was possible to identify the following species: Chara vulgaris L., C. globularis Thuiller, and Nitella hyalina (DC.) C.Agardh. The latter taxon formed a well-distinct community in the small pond LVN. According to Bazzichelli & Abdelahad [63], in Italy this species occurs in various habitats, such as ponds, lakes and running waters, and it is known from Lombardy, Veneto, Latium, and Sicily. Nitella hyalina characterizes the association Nitelletum hyalinae Corillion 1957, gravitating in the Nitellion flexilis alliance which includes Atlantic to sub-Atlantic communities of moderately acidic to neutral waters of low conductivity [64]. Although the association sometimes shows the co-presence of other charophytes, in particular of Chara [64], it can also form coenoses rich in vascular plants such as hydrophytes and helophytes or also very species-poor and almost monospecific communities [65]. In the study area, the association was in contact, on the one hand, with the Potamogetonetum natantis, on the other hand, with the hygrophilous vegetation of the shallow water near the shores, as evidenced by the presence of Peplis portula L., Alisma lanceolatum With. and Agrostis stolonifera L.

Utricularietum australis Müller et Görs 1960 (Supplementary Material Table S1, rel. 2)

This association is dominated by Utricularia australis R.Br., and occurs in mesotrophic to naturally eutrophic water bodies, such as alluvial pools and oxbows but also in flooded sand pits and newly established wetlands [66]. It shows pioneering behaviour, as recently pointed out by Viciani et al. [26] for some sites in the eastern Tuscan Apennines. In the study area, this community type was found at the Lake of Piane di Materazzo (LPM). The association developed in the shallow waters close to the shores, in a sheltered position at the edge of the reeds, as shown by the presence of several helophytic species in the relevé.

Potamogetonetum natantis Hild 1959 (Supplementary Material Table S1, rel. 3–8).

The coenoses dominated by Potamogeton natans L. were widely represented and detected in four sites (LMU, LDP, LVN, POM). These communities can be attributed to the association Potamogetonetum natantis Hild 1959, which occurs in oligo- to eutrophic water bodies with depths of 20–100 cm, with still or slowly flowing waters [67]. The association seems to be particularly widespread in small and low-depth water bodies, where it often forms very dense and paucispecific stands [26]. This is also confirmed in the study area, where P. natans forms rather species-poor communities, that develops mainly in shallow waters that are subject to drastic variations in depth during the seasons. The occurrence of Phragmites australis (Cav.) Trin. ex Steud. indicates the contact of Potamogetonetum natantis with the tall helophytes belt (Phragmitetum australis) while, in very shallow waters, the presence of small helophytes such as Eleocharis multicaulis (Sm.) Desv., Juncus bulbosus L. or Peplis portula indicates water dynamics favoring the affirmation of coenoses belonging to different classes during the summer desiccation period (e.g., Littorelletea or Isoëto duriei-Juncetea bufonii).

Potamogetonetum pusilli von Soó 1927 (Supplementary Material Table S1, rel. 9–12).

This association is typical of mesotrophic to eutrophic, clear waters of shallow parts of natural and artificial ponds, canals and rivers, especially along their lower courses, developing at different water depths, even in disturbed or early successional habitats [67]. In the study area, the association was found in three small ponds (AUN, LE, PE), all subject to severe summer desiccation. In all the sites it was characterized by the presence of Chara species. In the ponds near Roselle (LE, PE) the association occupied the central and deeper waters compared to the Ranunculion aquatilis coenoses which, instead, developed near the banks at a few centimetres of depth.

Parvo-Potamogetono-Zannichellietum pedicellatae De Soó 1947 (Supplementary Material Table S1, rel. 13–16).

According to Šumberová [67], stands dominated by Zannichellia palustris L. or mixed stands with Z. palustris and some narrow-leaved species of Potamogeton can be attributed to the association Parvo-Potamogetono-Zannichellietum pedicellatae, belonging to the Potamion alliance. In addition, this species can form communities also in brackish waters, gravitating in different syntaxes, such as the alliance Zannichellion pedicellatae.

The Parvo-Potamogetono-Zannichellietum pedicellatae grows in eutrophic to hypertrophic, often turbid, shallow freshwaters, mainly in ponds and pools and more rarely in slowly flowing streams [67]. In the study area, the association was found in two ponds (LC, PSB) where the ecological conditions and the floristic composition appear very similar. Zannichellia palustris grew on top of a dense layer of Chara species in the deepest part of the ponds, sometimes in contact with Potamo-Ranunculetum trichophylli association, present in shallower waters. This community is also subject to strong water fluctuations in the ponds and has already disappeared in early summer.

Potamogeton nodosus community (Supplementary Material Table S1, rel. 17).

In a highly disturbed pond (AUN) near Nomadelfia, in addition to the Potamogetonetum pusilli, a small stand dominated by Potamogeton nodosus Poiret was found. This vegetation type was characterized by an abundant presence of Chara vulgaris L. Although Potamogeton nodosus communities are sometimes considered to be typical of running waters, e.g., [68], their presence in standing waters is rather common [26,69]. The Nomadelfia community could therefore represent an impoverished aspect of the Potamogetonetum denso-nodosi O. de Bolòs 1957 association, included in the Potamion alliance, which has been reported in both standing and in flowing waters [70].

Potamogeton lucens community (Supplementary Material Table S1, rel. 18).

A small and sparse stand dominated by Potamogeton lucens L. was found at the lake of Piane di Materazzo (LPM). Despite the low total cover value, this population is rather rich in hydrophytes, due to the presence of P. nodosus, P. pusillus, and Utricularia australis. This community type represents an impoverished aspect of the association Potamogetonetum lucentis Hueck 1931, already reported for the southern Maremma (central Italy) by Lastrucci et al. [29].

Ranunculo ophioglossifolii-Callitrichetum stagnalis Brullo, Scelsi & Spampinato 2001 (Supplementary Material Table S1, rel. 19–26).

subass. typicum (Supplementary Material Table S1, rel. 19–21).

subass. ranunculetosum peltati subass. nova (Table S1, rel. 21–26) [holotypus rel. n. 26 Supplementary Material Table S1 hoc loco]

This association has been described for the Aspromonte Massif (southern Calabria) by Brullo et al. [71], and is typical of eutrophic depressions that have been flooded for a long time and dried out in summer. In the study area, this vegetation type was dominated by Callitriche stagnalis Scop., while Ranunculus ophioglossifolius Vill. was often present in the aquatic form with floating leaves. The subassociation typicum, as originally described by Brullo et al. [71] and according to the rules of the ICPN [57], was found at the edge of two very small ponds (LE, PSB), which are steeply sloping and occupied in the deepest parts by communities dominated by Potamogeton pusillus or Zannichellia palustris. At the edge of two larger ponds (LCE, PE), the presence of Ranunculus peltatus, sometimes with high cover, supports the description of the new subassociation ranunculetosum peltati (type relevé n. 26 in Table S1: wetland LCE; m² 4; total cover 95%; Callitriche stagnalis 3, Ranunculus ophioglossifolius +, Ranunculus peltatus 4, Mentha aquatica 2, Glyceria fluitans +). This subassociation grows in shallow waters that slope less steeply towards the deeper center, as indicated by the presence of palustrine species found in the wet soils around the ponds (Agrostis stolonifera, Glyceria fluitans (L.) R.Br., Ranunculus repens L.). The presence of Callitriche brutia Petagna highlights the potential for the development of the association Callitricho brutiae-Ranunculetum ophioglossifolii Gigante, Maneli & Venanzoni 2013. In the study area, this community finds its optimum at a later temporal stage, in late spring, when drying further reduces water depth until the humid bottom of the pool is left uncovered.

Callitricho brutiae-Ranunculetum peltati Pizarro & Rivas-Martinez 2002 subass. ranunculetosum trichophylli Lastrucci, Foggi, Selvi & Becattini 2007 (Supplementary Material Table S1, rel. 27–31).

In two sites of the southern Maremma, Lastrucci et al. [29] detected the association Callitricho brutiae-Ranunculetum peltati Pizarro & Rivas-Martinez 2002, describing two subassociations, one (ranunculetosum trichophylli) for the Lagaccioli site and another one (callitrichetosum obtusangulae) for the Marruchetone lake. After almost 20 years, the species of the association are still present in the Lagaccioli ponds. Although the water level was rather high during the survey season, some considerations can be made about the different frequencies of the different species in this community type. Callitriche brutia was found only in a small patch at one of the two ponds, at the edge of marsh vegetation, in very shallow water. It is possible that the depth of the water did not allow this species to be observed in other parts of the ponds. For Ranunculus peltatus Schrank, a situation similar to that reported by Lastrucci et al. [29] was observed, showing that only occasionally was this the dominant species. On the other hand, Ranunculus trichophyllus was almost always the dominant species in this community type, also forming populations in which the other two species were missing.

Potamo crispi-Ranunculetum trichophylli Imchenetzky 1926 (Supplementary Material Table S1, rel. 32–35).

Stands dominated by R. trichophyllus were also detected in other sites than Lagaccioli, such as the Casalino pond (LC). These Ranunculus trichophyllus dominated communities cannot be attributed to Callitricho-Ranunculetum peltati subass. ranunculetosum trichophylli due to the total absence of the association’s indicator species in the site. Instead, they can be referred to the association Potamo crispi-Ranunculetum trichophylli Imchenetzky 1926, in accordance with what has been reported from other sites in Tuscany [26,31] or from the “Altipiani di Colfiorito” site in Umbria [72]. It is possible that at the Lagaccioli site both syntaxa are present and a sort of balance between them is regulated by the hydrological levels, which favor or disfavor the development of Callitriche brutia and Ranunculus peltatus. Another aspect that could limit the development of these last two emergent hydrophytes is the marked increase, compared to the situation observed by Lastrucci et al. [29], of the aquatic ecophene of Persicaria amphibia (L.) Delarbre, present in almost all the Lagaccioli relevés, even with high cover values and a dominant role. In fact, Lastrucci et al. [29], pointed out that this species, with its terrestrial ecophene, was particularly competitive during the drying period of the ponds but not during the aquatic phase of the habitat.

Lemno-Callitrichetum obtusangulae (Philippi 1978) Passarge 1992 (Supplementary Material Table S1, rel. 36–37).

Callitriche obtusangula Le Gall communities can develop in both flowing and standing water habitats. In the first case, the coenoses are mainly associated with the Batrachion fluitantis alliance, while in the latter they are referred to as the Ranunculion aquatilis alliance [73,74]. The association Lemno-Callitrichetum obtusangulae represents a type of C. obtusangula-dominated vegetation reported for springs or small water bodies [73,74]. In the study area C. obtusangula-stands were only detected in one site (PSR), where the species covered almost the entire pond and developed over a layer of Chara sp. The association appears in an extremely impoverished form since only Ranunculus trichopyllus and Mentha aquatica were present.

Callitriche platycarpa community (Supplementary Material Table S1, rel. 38).

A small patch dominated by Callitriche platycarpa Kütz. was found in a small pond near Roselle, mainly occupied by communities belonging to Ranunculo ophioglossifolii-Callitrichetum stagnalis ranunculetosum peltati and to Potamogetonetum pusilli. Felzines [75] reported from France the association Veronico beccabungae-Callitrichetum platycarpae Grube ex Felzines 2016, which belongs to the Ranunculion fluitantis alliance and indicates the reophile character of this community, although this species can grow in different types of habitats [76]. In Italy, this species is rather rare, and in Tuscany in particular it is known mainly from old records [77], so the lack of recent distributional and phytosociological data could affect a comprehensive understanding of the communities formed by this species.

3.2. Palustrine Plant Communities

Isolepis cernua communities (Supplementary Material Table S2, rel. 1–2).

At the edge of the natural pool near to Frantoio Verrocchio (FV), during the late spring desiccation, two vegetation types characterized by small helophytes were observed behind a higher belt dominated by Eleocharis palustris (L.) Roem. & Schult. The first develops on still-moist soils due to the shade provided by the cork oak trees surrounding the pool. This community is rather dense and is dominated by Isolepis cernua (Vahl) Roem. & Schult., especially associated with Alisma lanceolatum, both with rather high cover. Isolepis cernua can form different communities belonging to syntaxa of the Isoëto duriei-Juncetea bufonii class [78,79], but it is often found in species-poor communities that are difficult to place at the association level (see also Lastrucci et al. [69,80]), as in the case of the study area.

Damasonium alisma communities (Supplementary Material Table S2, rel. 3–4).

A second type of vegetation was found close to the Isolepis cernua communities. It develops on soils that dry out earlier, so that at the time of the survey it appeared as solidified mud. This community differs from the previous one physiognomically, as it is much sparser, and floristically, due to the presence of the rare Damasonium alisma Mill. The species was considered a characteristic of the Isoëtetalia order [78], although it can participate to associations attributed to other syntaxa, such as Damasonio alismae-Crypsietum aculeatae (Verbenion alliance, according to Brullo & Minissale [78]). This association was described by Rivas-Martinez et al. [81] from the rather saline clay soils of the Guadalquivir brackish marshes in Spain and is characterized by the strong dominance of Sporobolus aculeatus (L.) P.M.Peterson, a species that is not present in the relevés of the study area.

The presence of small stands of Damasonium alisma in the southern Maremma and referred to the Isoëtetalia order, has already been reported along a thin strip of the dry bottom at the eastern Lagaccioli pond [29]. In this study, however, it was not possible to observe these stands again, probably due to the high water level at the time of the surveys.

Peplido portulae-Ludwigietum palustris Robbe ex J.-M. Royer, Felzines, Misset & Thévenin 2006 nom. mut. propos. (Supplementary Material Table S2, rel. 5–6).

Ludwigia palustris (L.) Elliott dominated communities were observed in two small ponds of the study area (LVM, POM), developing on the muddy shores that emerge during the late spring drying period. In Maremma, species-poor L. palustris communities have also been recorded in the Capalbio wetlands, at the Uccellina lake [29]. As pointed out by Lastrucci et al. [82] and Dítě et al. [83], L. palustris communities have been placed by several authors in different syntaxonomic classes, such as Bidentetea, Isoëto duriei-Juncetea bufonii, Littorelletea, or also Phragmito-Magnocaricetea. The presence of Peplis portula in one relevé allowed us to place the coenoses of the study area in the Peplido portulae-Ludwigietum palustris, a thermophilous association observed in different wetland types such as periodically inundated riverbanks, depressions, and water reservoirs gravitating in the alliance Eleocharition soloniensis Philippi 1968 (previously reported as Elatini-Eleocharition ovatae Pietsch 1973, today considered a synonym according to Mucina et al. [60]), of the class Isoëto duriei-Juncetea bufonii [83].

Callitricho brutiae-Juncetum bulbosi Gigante, Maneli & Venanzoni 2013 (Supplementary Material Table S3, rel. 1–2).

In one site (LVN) of the Mt. Leoni area, small stands of Juncus bulbosus and Peplis portula were observed. The presence of Callitriche brutia allowed us to assign these coenoses to the Callitricho brutiae-Juncetum bulbosi described by Gigante et al. [79] from some shallow ponds at the Ferretto site in Umbria, where the tufts of the dominant species Juncus bulbosus form small bulges separated by shallow water depressions. The relevés of the study area are more species-poor compared to those of Ferretto, and the spaces between the tufts of J. bulbosus are occupied by Peplis portula and sometimes by Potamogeton natans, probably configuring a deeper-water variant of the typical association.

Junco bulbosi-Eleocharitetum multicaulis (Passarge 1955) Passarge 1999 (Supplementary Material Table S3, rel. 3–5).

Eleocharis multicaulis was found forming dense stands along the partially flooded shores of some of the ponds and pools in the study area, on muddy soils gently sloping towards the submerged zones and also in more prolonged flooded areas, in contact with aquatic Potamogeton natans coenoses. On the outer drier edge, this community is in contact with the humid meadows with Gratiola officinalis L. or with the taller vegetation dominated by Molinia arundinacea Schrank and Schoenus nigricans L. From a phytosociological point of view, the community of the study area differs from the Eleocharitetum multicaulis Allorge ex Tüxen 1937 mainly from a floristic point of view, rather than from its synecology. This association represents a medium-low height amphibious turf developing on a more or less organic substrate [84] typical of oligotrophic and acidophilic habitats [85]. The association is characterized by species that are absent in the study area, such as Hypericum elodes L., Helosciadium inundatum (L.) W.D.J.Koch, Isolepis fluitans (L.) R.Br., Ranunculus baudotii Godr. (sub R. flaccidus subsp. confusus), or Potamogeton polygonifolius Pourr.; Eleocharitetum multicaulis can also show aspects rich in Sphagnum sp. pl. [86].

The more Mediterranean association Junco emmanuelis-Eleocharitetum multicaulis described by Rivas-Martinez et al. [81] appears to be very different from a floristic point of view, due to the presence of species with restricted distribution such as Juncus emmanuelis A.Fern. & J.G.García and Avellara fistulosa (Brot.) Blanca & C.Díaz. Therefore, it does not seem appropriate to assign the sampled communities to these associations. Passarge [87] described the association Junco bulbosi-Eleocharitetum multicaulis, which lacks the above-mentioned differential species and is rich in Phragmition species such as Lycopus europaeus L., Lythrum salicaria L., and Phragmites australis, and other hygrophilous species such as Juncus articulatus L. or Agrostis stolonifera, also present in the relevés. For these reasons, the E. multicaulis stands of the Maremma territory can be provisionally included in the latter association. It is possible that further studies in Mediterranean Tuscany, and possibly in other sites of the western Italian peninsula, will lead to the recognition of such communities as a distinct syntaxon.

Phragmitetum australis Savič 1926 nom. corr. (Supplementary Material Table S4, rel. 1–8).

This is a widespread association, quite common in Italy and Europe [88,89], developing in several types of wetlands, from meso- to eutrophic fresh or brackish waters, and on different types of soils. In the study area, however, the association was not very frequent and developed mainly in some wide and open ponds and small lakes (L1, LDP, LMU, LPM), where the shading of the surrounding forests was less intense. It developed on more or less flooded soils, in contact with aquatic or other marsh vegetation types, often forming belts of variable width around the water bodies.

Although the association and, more generally, P. australis stands have shown a serious decline in several large lakes in Italy [90], no signs of dieback (e.g., the clumping habitus) were observed in the study area. This is probably due to the fact that strong seasonal water fluctuations in the examined sites reduce the risk of permanent submergence, which seems to be an unfavorable ecological condition for the Phragmitetum [91]. The resurvey of the vegetation on the Lagaccioli sites confirmed the current presence of the association, already reported by Lastrucci et al. [29].

Lysimachia vulgaris community (Supplementary Material Table S4, rel. 9–10).

The presence of the Lysimachia vulgaris L. community in the western Lagaccioli pond (L1) has already been reported by Lastrucci et al. [29]. This association represented the more external hygrophilous community in contact with the woody vegetation around the pond. The relevés confirmed its presence on the site, where it appeared more widespread and abundant than in the past, probably at the expense of other communities such as the Sparganietum, which is currently restricted to the opposite bank of the ponds and no longer in contact with the Lysimachia stands, as reported by Lastrucci et al. [29]. Although Lysimachia vulgaris is found in communities belonging to different syntaxes, see Lastrucci et al. [29], the presence of helophytes and also some hydrophytes in the Lagaccioli stands, due to the prolonged submergence, confirms the position of these coenoses in the Magnocaricetalia order, Lastrucci et al. 2007 [29], and the Magnocaricion elatae alliance [92].

Glycerio-Sparganietum neglecti Koch 1926 (Supplementary Material Table S5, rel. 1).

A stand with Sparganium erectum sensu latu was found in the western pond of Lagaccioli (L1), forming a narrow belt between aquatic coenoses with Ranunculus trichophyllus or Persicaria amphibia and Phragmitetum australis communities. According to Landucci et al. [88,89], Glycerio-Sparganietum neglecti Koch 1926 should be considered as a “macro-association” including other associations recognized in the past, such as Sparganietum erecti Roll 1938 and Sparganietum microcarpi (Weber 1976) Passarge 1978, due to the frequent uncertain taxonomic identification of the species in this group, see for Italy Lastrucci et al. [93]. This research could not confirm the presence of the association in the eastern Lagaccioli pond (L2), where it had been previously indicated by Lastrucci et al. [29].

Glycerietum fluitantis Nowinski 1930 nom. inval. (Supplementary Material Table S5, rel. 2–3).

The communities belonging to this association develop mainly on habitats in advanced stage of terrestrialization or periodically flooded, such as ponds, banks of canals, and streams or flooded depressions [88]. Although G. fluitans is rather common in the study area, coenoses dominated by this species and belonging to the association were only found in two ponds (LCE, PL). These were developed on shallow waters, in contact with aquatic coenoses and Eleocharitetum palustris, respectively, and well-tolerating strong water fluctuation [94]. Concerning the nomenclatural problems of this association, see Lastrucci et al. [27]. This survey could not confirm these communities at the Lagaccioli sites (L1, L2), where they were previously reported by Lastrucci et al. [29].

Alismo lanceolatae-Gratioletum officinalis Biondi & Bagella 2005 (in mosaic with Junco tenageiae-Solenopsietum laurentiae Gigante, Maneli & Venanzoni 2013) (Supplementary Material Table S5, rel. 4–6)

Gratiola officinalis typically develops in areas with wet soils for a fairly long period in spring, but dries up in the summer, see Gigante et al. [79]. From a syntaxonomic point of view, similar to the coenoses of the Ferretto (Umbria) site [79], it forms communities that represent an impoverished aspect of the Alismo lanceolatae-Gratioletum officinalis, described by Biondi & Bagella [95] from the Maddalena Archipelago (Sardinia). In the study area, the species formed dense stands along the wet shores of two small ponds (LPM, LTC). The presence of Juncus conglomeratus L. in one relevé suggests that the subassociation juncetosum conglomerati Gigante, Maneli & Venanzoni 2013 may also occur in the study area.

However, it is important to note that the floristic composition is very peculiar in at least two relevés, with a well-defined pool of small hygrophytic species, such as Solenopsis laurentia (L.) C.Presl, Juncus tenageia L.f., J. pygmaeus Rich. ex Thuill., Cicendia filiformis (L.) Delarbre, Centaurium maritimum (L.) Fritsch, Juncus bulbosus, and Eleocharis multicaulis. Many of these species were also found at the Ferretto site by Gigante et al. [79], where they formed acidophilic communities placed in the associations Junco tenageiae-Solenopsietum laurentiae Gigante, Maneli & Venanzoni, 2013 and Solenopsio laurentiae-Juncetum pygmaei V. Silva & Galán de Mera in V. Silva, Galán de Mera & Sérgio 2008, with the subassociation isolepidetum cernuae Gigante, Maneli & Venanzoni 2013. At least one of the relevés (Table S5, rel. 6), with rather high cover of Solenopsis laurentia, could be considered as an aspect of the Junco tenageiae-Solenopsietum laurentiae in mosaic with the Alismo-Gratioletum association; also, rel. 4 of Table S5 was rather rich in small annual helophytes.

It remains unclear whether the presence of Gratiola offinalis, with its higher biomass and shading effect, could be detrimental to the above small species. To this purpose, monitoring of this vegetation would help to understand whether the Alismo-Gratioletum, given the pioneering nature of its dominant species, is a community that expands to the detriment of others, or whether the mosaic of species of different sizes remains stable over time.

Eleocharitetum palustris Savič 1926 (Supplementary Material Table S5, rel. 7–13).

The communities belonging to this association have a strong pioneer character and are relatively common in Italy [88,96]. Lastrucci et al. [27] reported that the Eleocharitetum palustris association is particularly common in small ponds and pools, where it forms narrow strips or small stands, often in shallow waters and disturbed habitats. In the study area, these patterns were confirmed, and the association was also found in very small pools subject to rapid drying, often in contact with the Glycerietum fluitantis association. Due to the quick drying in late spring, in some very small areas such as the Frantoio Verrocchio pool (FV), the Eleocharitetum palustris is present in dense stands only in the more humid central areas, while it is unable to develop in the early drying marginal areas, where the empty spaces are occupied by vegetation of small helophytes in mosaic with it. The resurvey of the vegetation at the Lagaccioli sites confirmed the presence in L1 of the association previously reported by Lastrucci et al. [29].

Oenantho aquaticae-Rorippetum amphibiae Lohmeyer 1950 (Supplementary Material Table S5, rel. 14–19).

The association develops on periodically flooded habitats with strong water fluctuation and drying out in summer, such as depressions at the bottom of river and stream floodplains, shorelines of dead branches and artificial water reservoirs, or slow-flowing lowland stream beds that may be overgrown with vegetation [97]. The habitats are often eutrophic, and the substrate consists of a layer of mud and organic material of varying thickness. In the study area, the association was only found at the Lagaccioli sites (L1, L2), where it was formerly reported by Lastrucci et al. [29]. According to these authors, the association can be dominated by Rorippa amphibia in some stands and by Oenanthe aquatica in others. The relevés confirmed the presence of a variant with Persicaria amphibia, sometimes becoming the dominant species, as previously suggested by Lastrucci et al. [29].

Bolboschoenetum glauci Grechushkina, Sorokin & Golub 2011(Supplementary Material Table S5, rel. 20).

In the Lagaccioli lakes, Lastrucci et al. [29] reported the presence of Bolboschoenus maritimus (L.) Palla vegetation (sub Scirpetum maritimi (Christiansen 1934) R.Tuxen 1937). During this study, it was confirmed that the species present at this site is Bolboschoenus glaucus (Lam.) S.G.Sm., based on the taxonomic revision by Di Natale et al. [98]. Consequently, the corresponding community can be attributed to the Bolboschoenetum glauci association, already reported from the nearby Acquato Lake in southern Maremma [30]. The association was detected in a restricted area of the western pond (L1), but it could be favored by the summer drying and thus develop on larger areas later in the season.

Callitricho brutiae-Ranunculetum ophioglossifolii Gigante, Maneli & Venanzoni 2013 (Supplementary Material Table S6, rel. 1–5).

Ranunculus ophioglossifolius Vill. was rather common in the study area and was found to form dominated or co-dominated communities in at least four sites. Dominated communities of this species in Italy have been described by Biondi et al. [99] as Trifolio fragiferi-Ranunculetum ophioglossifolii for the Marche region, and by Gigante et al. [79] as Callitricho brutiae-Ranunculetum ophioglossifolii for some peculiar small acidophilic inland temporary ponds near Trasimeno Lake (Ferretto site, Umbria). Both the associations were included in the alliance Oenanthion fistulosae de Foucault 2009 (for nomenclatural and syntaxonomic aspects see Mucina [60]) of the class Molinio-Arrhenatheretea. In addition, Brullo et al. [71] described the association Veronico beccabungae-Ranunculetum ophioglossifolii, included in the Montio-Cardaminetea class, for some running-water habitats of the Aspromonte territory (Calabria, southern Italy).

As for the communities of the study area, several floristic and ecological affinities with Callitricho-Ranunculetum can be found, both for the presence of Callitriche brutia in some of the relevés and for the hydrological dynamics of the habitats, characterized by strong seasonality. Also, the presence of Glyceria fluitans in some more humid areas (Supplementary Material Table S6, rel. 3–5) supports the affinity with the association Callitricho-Ranunculetum by Gigante et al. [79], representing transitional aspects towards the subassociation glycerietosum fluitantis Gigante, Maneli & Venanzoni 2013. Gigante et al. [79] observed the large variability in the syntaxonomical interpretation of the communities with Ranunculus ophioglossifolius, ranging from aquatic syntaxa of the Ranunculion aquatilis alliance, to small helophyte syntaxa of the Isoëto duriei-Juncetea bufonii or Littorelletea classes, to Glycerio-Sparganion alliance and, as already mentioned, Montio-Cardaminetea and Molinio-Arrhenatheretea classes. Concerning the Callitricho brutiae-Ranunculetum ophioglossifolii in particular, neither the growth forms, the habitat, nor the phytogeographical characteristics of the examined sites seem particularly congruent with its inclusion in syntaxa of the order Molinetalia ceruleae, which includes wet meadows on mineral and peaty soils in temperate to subarctic zones of Europe [60]. One relevé (rel. 5) near “Poggio Romano” (LPR), with the presence of amphibious patches of Callitriche stagnalis, was considered here as a transitional aspect between an impoverished aspect of Callitricho-Ranunculetum and the aquatic association of Ranunculo ophioglossifolii-Callitrichetum stagnalis Brullo, Scelsi & Spampinato 2001.

Molinietum arundinaceae Trinajstič 1965 variant with Schoenus nigricans (Supplementary Material Table S6, rel. 6–7).

Molinia arundinacea-dominated communities have been reported for several types of freshwater habitats, such as wet depressions along rivers [96,100,101] or lakes [82], as Molinietum arundinaceae Trinajstič 1965. For some wet areas in the ultramafic soils of the Upper Tiber Valley (eastern Tuscany), Lastrucci et al. [80] reported a variant of the association with high presence of Schoenus nigricans, showing some affinities with the association Molinio arundinaceae-Schoenetum nigricantis Rivas-Goday 1945 indicated for the Iberian Peninsula by Rivas-Martinez et al. [102]. According to Rivas-Goday [103], the variant dominated by Molinia arundinacea represents a transitional aspect between the association Molinio-Schoenetum nigricantis and the woody heath vegetation dominated by Calluna, Ulex, and/or Erica species. In the study area, stands of Molinia arundinacea and Schoenus nigricans grew on gentle slopes surrounding the Eleocharis multicaulis vegetation near the shores of a pool (SDP) in the Mt. Leoni area. Among the other species characterizing M. arundinacea stands, some acidophilic or subacidophilic herbs were present, such as Potentilla erecta (L.) Raeusch., Carex punctata Gaudin, Succisa pratensis Moench, or Danthonia decumbens (L.) DC. In this vegetation type, the transition towards shrub acidophilic vegetation was indicated by Calluna vulgaris (L.) Hull.

Juncus effusus community (Supplementary Material Table S6, rel. 8–9).

Juncus effusus L. was often observed in stands along the shores of lakes and ponds, forming a belt that represented the boundary between the aquatic vegetation and the terrestrial communities surrounding the wetland area. This vegetation type was generally rich in more or less hygrophilous species, and represented a transition between the marsh coenoses of the class Phragmito-Magnocaricetea and the wet meadows of the Molinio-Arrhenatheretea classes, see Lastrucci et al. [29,82,104,105]. In the study area, dense Juncus effusus-dominated coenoses were detected around the lake near the Neolithic village (LVN) of the Mt. Leoni area.

According to Landucci et al. [89], when Juncus effusus communities are not particularly rich in elements of the Phragmito-Magnocaricetea class, it is preferable to place them in the Molinio-Arrhenatheretea class. The same interpretation has been applied to the Juncus effusus belt around the “Stagnone” lake of Capraia Island in the Tuscan Archipelago [105].

3.3. Conservation Notes

It is worth noting that nine of the nineteen sites are not included in protected areas, and that, of these, only the Lagaccioli lakes (L1, L2) were already known to be of conservation relevance [29,47,106,107]. The vegetation of all the other water bodies surveyed was previously unknown and examined here for the first time, although some of them are included in Natura 2000 sites (protected areas of European importance, see [108]), and floristic collections were made years ago by Selvi [37,109]. Considering that the habitats worthy of conservation at the European level and listed in the Habitats Directive [108,110] are mostly based on vegetation types [111,112,113,114,115,116,117,118], this study allows us to recognize the habitat types present in the study area. Recent scientific works have pointed out that not all the habitats of real conservation importance in southern Europe and the Mediterranean are listed in the Annexes of the Habitats Directive [89,119,120]. However, among those recognized in the Directive, several are considered important at the continental scale and some others at the local scale. As shown in Supplementary Material Table S7, some of the detected communities can be attributed to the habitat “Oligotrophic to mesotrophic standing waters with vegetation of the Littorelletea uniflorae and/or Isoeto-Nanojuncetea”, some others to the habitat “Natural eutrophic lakes with Magnopotamion or Hydrocharition-type vegetation”. The Nitella-dominated communities belong to the habitat “Hard oligo-mesotrophic waters with benthic vegetation of Chara spp.”, while the coenoses with Molinia arundinacea and Schoenus nigricans belong to the habitat “Mediterranean tall humid herb grasslands of the Molinio-Holoschoenion”. The communities that can be attributed to the habitat “Mediterranean temporary ponds” (see Supplementary Material Table S7) are particularly relevant, as these environments, rich in rare species, are considered to be of priority importance for conservation at the European level [13,109].

4. Conclusions

This study has shown that detailed field studies, even in areas considered well known from a floristic and naturalistic point of view such as Tuscany, can bring to light novel data or update existing information documenting the presence of rare species and plant communities of conservation interest. A total of 28 phytocoenoses were identified and classified into seven syntaxonomic classes, and a new to science subassociation was described. The identification of the site-associated Natura2000 habitats led to the recognition of five habitats of conservation interest at the national and European level.

In sum, the present study allows us to improve the knowledge of the flora and vegetation of small but valuable wetland sites, for 17 out of 19 of which the biodiversity present was previously completely unknown, providing a basis for their preservation and demonstrating that the acquisition of taxonomic and syntaxonomic knowledge based on herbarium and field surveys is still fundamental for nature conservation [121,122]. The main challenges for the future are to continue this type of research in similarly neglected areas, as it has proven to be very fruitful in increasing knowledge of biodiversity, and then, an even more difficult task, to focus on how the land-managing Administrations can act to conserve the biodiversity detected.