Phytosociological research on temporary ponds in Apulia (southern Italy)

The ephemeral hygrophilous vegetation occurring in the temporary ponds of Apulia (southern Italy) weres studied following the phytosociological approach. On the base of 153 phytosociological relevés carried out during the period 2015-2018, 19 associations were identified, of which 16 described for the first time. All the associations belong to the Isoeto-Nanojuncetea class. The surveyed associations can be arranged in two orders, such as Isoetetalia, including those with a winter-spring cycle and Nanocyperetalia, regarding those with a summertime cycle. The identified association has been examined in detail, and for each one, we provided a phytosociological table. The communities belonging to the Isoetetalia are 17 and arranged in four alliances (Isoetion, Preslion cervinae, Cicendio filiformis-Solenopsion laurentiae, Agrostion salmanticae); instead, those ones of Nanocyperetalia are two both included in the Verbenion supinae. In order to highlight the relationships among the associations, all the relevés used for this investigation are processed. Overall, this analysis confirms the autonomy of the associations, grouping them according to the syntaxonomic arrangement proposed by the authors. Taxonomic investigations on the flora occurring in these habitats allowed the detection of two new subspecies of Solenopsis laurentia, both with a different autoecology.


Introduction
One of the extremely specialized wet habitats, occurring in Europe and southern Mediterranean territories, rich in ephemeral hydrophytes of exceptional geobotanical value, is represented by temporary ponds, which are periodically flooded by rainwater, mainly during the autumn-winter time. These surfaces remain usually submerged until the late spring and, sometimes, also in the early summer (Grillas et al., 2004). These very peculiar stands, characterized by silt-clay soils deposited on impermeable substrates, are colonized by ephemeral plant communities linked to temporarily submerged soils. Based on the environmental conditions, mainly regarding the flooding period, two types of plant communities can be recognized, which are seasonally well differentiated. The first group includes associations mostly characterized by microphytes showing an erect habit, with early-flowering (winter-spring), localized in stands with shallow waters drying up already in spring. The second group gathers plant communities floristically and physiognomically quite diversified from the previous ones, since dominated by therophytes usually with prostrate or prostate-ascending habit and showing later phenology (summer), linked to habitats submerged for a long time.
Based on these studies, the temporary ponds occurring in the Euro-Mediterranean territories can be included in a single class floristically, ecologically, and physiognomically well characterized and also differentiated from the structural point of view. This syntaxon is represented by the Isoeto-Nanojuncetea, class proposed by Braun-Blanquet & Tüxen (1943) as nomen nudum and after validated by Westoff et al. (1946). Within this class, two orders can be recognized, gathering communities seasonally well circumscribed and differentiated by a pool of species with habit and phenology markedly diversified, such as Isoetetalia Braun Blanquet 1935 and Nanocyperetalia Klika 1935. The first syntaxon is distributed in territories with Mediterranean bioclimate and is differentiated by ephemeral hydrophytes showing thermophilous requirements and having an early spring life cycle. The communities belonging to this order colonize oligotrophic wet soils dried up already in spring. As concerns the second syntaxon, it shows a Mediterranean-Atlantic and continental distribution occurring in territories characterized by Mediterranean and Temperate bioclimate (Rivas-Martinez et al., 2001). Floristically, it is differentiated by annual meso-hygrophilous species having summer-autumnal phenology, which grow on oligomesotrophic and eutrophic (sometimes halomorphic) soils.
On the whole, our researches, apart from improving the knowledge on the flora of these habitats, have allowed identifying in this territory nineteen associations, three of which already known for other Mediterranean countries but not yet recorded from Apulia, while sixteen are described as new associations. Finally, this work is provided by a multivariate analysis, where all the relevés used for this phytosociological study are processed.

Study area
As concerns the Apulia territory, several floristic, ecological and phytosociological contributions provide a quite complete and detailed framework on these peculiar wet habitats (Ernandes 2011, Ernandes et al. 2006, 2010a, 2010b, 2011, Ernandes & Marchiori 2012, 2013, Pesaresi et al. 2018. In order to improve this knowledge, the results of phytosociological investigations carried out in several places of Apulia region, mainly in the southern part, corresponding to the Salento peninsula, are here provided. In particular, the surveyed localities are reported in Figure 1 and listed in Appendix 2, where are reported their coordinates. A Mediterranean pluviseasonal oceanic bioclimate characterizes the study area with thermomediterranean thermotype and drysubhumid ombrotype (Rivas Martinez et al. 2001). As concerns the substrata, they are represented mainly by Cretaceous-Miocene limestones, often characterized by karst phenomena, and Plio-Pleistocenic calcarenites (Pieri et al., 1997;Sansò et al., 2015). The habitats colonized by plant communities belonging to Isoeto-Nanojuncetea are usually represented by wetlands periodically flooded by rainwater during the autumn-winter season. In the surveyed territory, they are not very frequent with a scattered distribution, occurring both along the coastal belt and inland. According to Ernandes & Marchiori (2013) and Ernandes et al. (2017), the wet habitats colonized by plant communities belonging to Isoeto-Nanojuncetea can be classified into four main types, such as: Figure a) Cupular pools, better known as rocky pools, which are usually small catchment depression on flat outcrops arising from limestone dissolution. The bottom of these ponds is covered by a thin layer of soil, submerged by shallow water, characterized by associations regarding the Isoetion or Preslion cervinae. b) Dolines, they are broad depressed surfaces periodically flooded by rainwater with deep and poorly permeable soils, created by karst phenomena or for subsidence. Usually, in these habitats, there are communities of the Agrostion salmanticae and Verbenion supinae. c) Waterlogged soil, they correspond to a more or less large hollow with impermeable surfaces often localized in the wood clearing and covered by a thick layer of clay-silt soil often abundant in the sandy component. These stands are submerged by shallow rainwater for short periods, and the plant communities belong mainly to Cicendio-Solenopsion laurentiae. d) Temporary streams, they are tiny and shallow watercourses, already dried up in late spring but with soils that remain moist for a long time. These habitats are infrequent and are colonized by impoverished vegetation of Verbenion supinae.

Floristic nomenclature
On the whole, the flora linked to the stands colonized by Isoeto-Nanojuncetea communities is well specialized and usually exclusive of these wet habitats. As concerns the floristic nomenclature, we have followed Pignatti (2017Pignatti ( -2019 and, in some cases, also Troìa & Greuter (2015) and Bartolucci et al. (2018). The checklist of the species occurring in the phytosociological relevés is reported in Appendix 3. Besides, during our field survey, it was collected Poa jubata, a very rare species having a South-East European distribution, which is a new record from the Italian flora (Cabi et al., 2017, Brullo et al., 2019. Another interesting finding concerns two very unusual plants belonging to Solenopsis laurentia cycle, which differ morphologically quite well from the typical population of this species. Basing on preliminary investigations, Solenopsis laurentia is a species complex, on which a taxonomic study is ongoing in order to emphasize the real role of these critical populations. For the moment, we consider it appropriate to treat them as subspecies of S. laurentia (L.) C.Presl and named subsp. caespitosa and subsp. pusilla. They are described in Appendix 1.

Data analysis
Vegetation data were sampled in the field between 2015 and 2018. A total of 153 relevés were carried out, according to the phytosociological approach (Braun-Blanquet, 1964;Westhoff & Der Maarel, 1978), with plot size ranging from 0.5 to 15 m 2 . The surveyed localities are reported in Figure 1 and listed in Appendix 2.
The initial matrix consisted of 160 relevés x 159 species, and, in order to highlight the floristic correlations among different plant communities, the data set was subjected to multivariate analysis. Cover values were transformed according to the method proposed by Der Maarel (1979). Different clustering methods were employed, on both presence/absence and cover data, by using different combinations of distance measures (Jaccard, Euclidean, Bray-Curtis) and group linkage methods (single link, complete link, UPGMA, Flexible beta), in order to visualize the general data structure and to detect the presence of outliers. Species with a frequency lower than 2% were removed from the dataset. The resulting final data matrix consisted of 150 relevés and 127 taxa.
Hierarchical clustering on the final matrix was performed by using flexible beta linkage, with the Bray-Curtis coefficient. Beta was set at -0.25 so that flexible beta clustering became a space-conserving method (McCune & Grace, 2002). To determine the optimal number of clusters, we have used the "Optimclass 1" method (P < 10 -6 ) (Tichý et al., 2010), applying the function "Crispness of Classification" to each data set partition.
Diagnostic species of the vegetation units (partitions) were determined through the calculation of their fidelity (phi coefficient); non-significant values of phi at P = 0,005 were excluded based on Fisher's exact test (Tichy & Chytry, 2006). Then, the syntaxonomic identification of the obtained partitions was carried out on the basis of the analysis of their diagnostic species, using the author's own expert knowledge and literature.
For the ordination analyses, we carried out a Nonmetric Multidimensional Scaling (NMDS) with a 'slow and thorough' option of the auto-pilot mode, using the Bray-Curtis coefficient as a dissimilarity measure (Clarke 1993). Hierarchical clustering and ordination analysis were run by PCOrd version 6.08. Optimclass and Crispness of Classification, as well as the determination of diagnostic species described above, were performed by software JUICE (Tichý, 2002).

Results and Discussion
Within phytosociological research carried out in Apulia, a contribution concerning the plant communities belonging to Isoeto-Nanojuncetea class, occurring in this territory of southern Italy, is provided. Previously, this class was examined by Ernandes & Marchiori (2013) and Ernandes et al. (2017), who recorded several associations belonging to various alliances, such as Isoetion, Preslion cervinae, Cicendio filiformis-Solenopsion laurentiae, Verbenion supinae. Basing on personal relevés regarding the Apulian wet habitats where this peculiar vegetation occurs, it was possible to recognize numerous associations, well differentiated from the floristic and ecological point of view, most of which can be attributed to the Isoetetalia order since characterized by species with spring phenology, while the summer-autumnal communities of the Nanocyperetalia are very rare because of the lacking in the study area of large pools suitable for this vegetation kind.
The Optimclass diagram showed a peak of faithful species at 22 partitions of the data-set. Also comparing with the Optimclass diagrams obtained by other clustering methods (e.g. flexible beta, Euclidean distance; UPGMA, Bray-Curtis; UPGMA, Euclidean), the optimal partitions turn out to range from 18 to 24. Nev-ertheless, the Crispness of Classification indicated the clearest separations at 3 and 6 clusters.
To detect plant communities and according to Optimclass analysis, the dendrogram was pruned to give 19 clusters of relevés ( Figure 2). The groups thus identified correspond to the surveyed associations, wholly autonomous from a floristic and ecological point of view.  On the whole, from the multivariate analysis, the associations identified result quite well differentiated from each other, since arranged in distinct clusters.
Indeed, as showed in Figure 2, three main clusters can be detected, which are separated in ecological groups. The first to disjoin is cluster C, including the associations occurring mostly in doline habitats, represented by large depressed surfaces periodically flooded with deep soils, that belong to Agrostion salmanticae. These plant communities are physiognomically characterized by species showing a big size with high coverage values. As regards the other associations, they segregate into two distinct clusters, of which the cluster B is more homogeneous, including more or less acidophilous associations linked to waterlogged soils, localized in large hollows or woodland clearings, rich in fine sediments, and are represented by Cicendio-Solenopsion laurentiae communities. They are differentiated mainly by very small erect species, which show a more or less thinning coverage. Finally, cluster A turns out to be the most heterogeneous, because it includes, apart from the Preslion cervinae associations, which are the most represented and rich in creeping amphibian species, also that microphytic one of the Isoetion, both included in the subcluster A1, related to the communities growing in the cupular pools. The Verbenion supinae associations form a distinct cluster (A3) closely related to that one regarding the peculiar Elatine alsinastrum community (A2) belonging to Preslion cervinae, both localized in large hollows usually used as pastures, with well nitrified soils.
The NMDS ordination results in a three-axis solution, with final stress of 16.6. The three axes account for 88.7% of the variance in the Bray-Curtis dissimilarity matrix (first axis 47.8%, second axis 24.7%, and third axis 16.2%). Results of the NMDS ordination approximately confirm the general pattern highlighted by the cluster analysis. In the NMDS 3D diagram (not shown), the Agrostidion communities (blue triangles) sharply separate, along with axis 1, from the other alliances. Along the axis 2, the communities of Cicendio-Solenopsion segregate from those of Preslion cervinae and Isoetion. As already highlighted in the dendrogram, the relevés of Isoetion get mixed up with those of the Preslion, mainly because they are floristically impoverished and scarce. As regards the Verbenion supinae communities, they are partially mixed with those of Preslion and Isoetion, especially along the axis 1, while segregating quite well along the axis 3. This general pattern is confirmed even when considering the arrangement of the relevés at the level of individual plant communities in the NMDS 2D (axis 1-2) diagram ( Figure 3).
As concerns the syntaxa surveyed in Apulia, they are reported in the following syntaxonomical scheme:   Structure and ecology: Ephemeral amphibious vegetation occurring in temporary ponds on soils periodically flooded by oligotrophic, eutrophic, or, rarely, sub-salt waters (Brullo & Minissale, 1998;Biondi et al., 2014). Floristically, these plant communities are dominated by hygrophilous therophytes or sometimes by small hemicryptophytes and geophytes. Structure and ecology: Pioneer ephemeral vegetation with thermophilous or sub-thermophilous requirements linked to oligotrophic soils dried up in spring (Brullo & Minissale, 1998;Biondi et al., 2014). Usually, it is characterized by hygrophilous microphytes having an early spring blooming.
Geographical distribution: This order shows a Mediterranean and South Atlantic distribution.
Isoetion Br.-Bl. 1935 Syn Structure and ecology: Pioneer and fleeting vegetation localized mainly in cupular pools rich in quillworts and microphytes with early spring blooming, linked to warm Mediterranean climate. It colonizes small surfaces represented by calcareous rocky pools with very shallow silty soils that dry up very early.
Geographical distribution: This alliance has a Mediterranean distribution. Characteristic species: Myosurus minimus, Bulliarda vaillantii. Structure and ecology: In small rocky pools of a calcareous plateau, near the coast, hygrophilous vegetation characterized by Bulliarda vaillantii and Myosurus minimus has been found. These species grow together with a few other microphytes linked to these peculiar temporary wet habitats submerged by shallow waters. For its floristic and ecological features this plant community can be referred to Myosuro minimi-Bulliardetum vaillantii, association described by Braun-Blanquet (1935) and also quoted by Braun-Blanquet et al. (1952) from southern France, where occurs in basaltic rocky pools.

Myosuro minimi-Bulliardetum vaillantii
Geographical distribution: In Apulia the association is very rare and seems localized in only one locality of the North Gargano area. It is recorded, other than in South France (Braun-Blanquet, 1935;Barbero et al., 1982), also in Spain by Rivas Goday & Ocaña García (1958) and Rivas Goday (1964). Structure and ecology: The association occurs in large rock pools near the sea, constituted by calcarenite substrates, which are flooded by rainwater affected by the sea aerosol. Physiognomically, it is characterized by Ranunculus saniculifolius and Callitriche brutia, rhizophytes usually growing together with Isolepis cernua, and some species of Lythrum. This vegetation seems to have its optimum in coastal stands, on rocky outcrops near salt-marshes, while it is quite rare in the inland stands.

Ranunculo ophioglossifolii-Callitrichetum brutiae ass. nova hoc loco
Structure and ecology: The association is localized in broad calcareous depressions characterized by deep silty-clay soils submerged for long periods by rainwaters, which are quite far from the sea. Usually, it covers the central part of the flooded surfaces where the water level is deeper. This vegetation is dominated by Ranunculus ophioglossifolius and Callitriche brutia, rhizophytes associated with Ranunculus saniculifolius that can reach high coverage values. For its ecology and dominance of Callitriche brutia, this association is related to Ranunculo lateriflorii-Callitrichetum brutiae Brullo & Minissale 1998, described from southern Sicily and belonging also to Preslion cervinae.
Geographical distribution: Currently, it seems circumscribed to a locality named Contr. Foresta near Cutrofiano (Lecce). Structure and ecology: This is a very peculiar association, which is differentiated by the occurrence of Elatine alsinastrum, species very rare in Italy (Pignatti, 2017, 2: 313). In Apulia this species has been recently recorded by Russo (2013) from Gargano and Ernandes & Marchiori (2013) from Salento, where it occurs in two places. In particular, the association has been described by us in a large wetland near Lecce, stand characterized by deep silty-clay soils submerged for a long time. From the phytosociological point of view, this vegetation may be attributed to its ecology and floristic set to Preslion cervinae, alliance here represented by Callitriche brutia and Ranunculus ophioglossifolius. Among the characteristic species of high rank are frequent Mentha pulegium, Lythrum borysthenicum, Lotus parviflorus, Trifolium dubium. As concerns the habitat colonized by this vegetation, it is much more like to those related to the communities of Verbenion supinae, rather than those of the Preslion cervinae, but the species of the first alliance are entirely missing. Previously, associations characterized by Elatine alsinastrum were described from Germany, as Elatini alsinastri-Juncetum tenageiae  Rivas-Martinez et al. (1980), indicating it as Callitricho platycarpae-Elatinetum alsinastri, but belonging, for its ecological and floristic peculiarity, to the Potametea class. Geographical distribution: Basing on the current surveys, this association occurs only at Zello near Cutrofiano. Table 3. Ranunculo ophioglossifolii-Elatinetum alsinastri ass. nova (rel. 1-7), Ranunculo saniculifolii-Elatinetum macropodae ass. nova (rel. 8-17) (Preslion cervinae, Isoetetalia, Isoeto-Nanojuncetea) Altitude (m asl) 115 115 115 115 115 115 115 1 1 1 1 1 1 1 1 1 1 Plot size (m 2 ) 5 5 5 5 5 5 5 3 4 2 2 1 1 1 1 1 1 Total cover (1=10%) 10 10 10 10 10 10 10 9 7 8 6 8 10 10 10 10 10 Species N. 9 10 9 12 11 9 9 9 14 10 15 12 7 9 10 11 10 Relevé N. Structure and ecology: This association is localized in calcarenitic rocky pools submerged up to the early spring by rainwater, weakly salty due to the marine aerosol, given their proximity to the sea. Floristically, it is differentiated by Elatine macropoda and Bulliarda vaillantii, having high coverage values and growing together with Ranunculus saniculifolius and several other hygrophytes of Isoeto-Nanojuncetea. This vegetation is replaced in the stands flooded by deeper water by the Isolepido cernuae-Ranunculetum saniculifolii, with which it is often in contact. In a recent contribution, Ernandes et al. (2017) presented numerous relevés, from various Apulian localities, which at least in part could be attributed to this association, even though they are floristically very poor or in some cases rather heterogeneous. In fact, these relevés are mixed with moss communities and were referred to different plant communities, such as Crassulo vaillantii-Ptychostometum capillaris Ernandes et al. 2017, Lythro hyssopifoliae-Crassuletum vaillantii Bagella et al. 2009or Elatinetum macropodae Br.-Bl. 1931. According to literature data (Brullo & Minissale, 1998), associations rich in Elatine macropoda similar to that one at issue, but well differentiated from floristic and ecological viewpoint, are: a) Apio crassipis-Elatinetum macropodae, described by Bagella et al. (2009)  Structure and ecology: This association occurs in the large temporary ponds, limitedly to small areas with deeper waters. The habitat is represented by karst depression somewhat distant from the coast, constituted by calcarenitic rocks covered with silty-clay soils. In this vegetation dominated by Isoetes longissima, it is localized Pilularia minuta, small fern very rare in the Mediterranean and also in Italy (Daoud-Bouattour et al., 2009;Mascia et al., 2013;Minissale et al., 2017). As concerns Apulia, it is currently reported only for two localities, such as Piano di San Martino on Gargano (Russo, 2013) and Salento near Nardò (Beccarisi et al., 2009;Ernandes et al., 2010). From the phytosociological viewpoint, the association at issue belongs to Preslion cervinae, for the occurrence of Ranunculus saniculifolius and Callitriche brutia, which grow together with several species of Isoeto-Nanojuncetea. Previously, this plant community was attributed by Ernandes et al. (2017) to Junco pygmaei-Isoetetum velatae, association described by Rivas Goday (1956) and later re-examined by Rivas Goday (1970) and Rivas-Martìnez et al. (2002), indicating it as pilularietosum minutae subass. nova. As concerns this attribution, it should be noted that the latter association is clearly different from that one in question both for its ecology and for the absence of Pilularia minuta, Eleocharis multicaulis, Isoetes todaroana,  (Paradis & Finidori, 2005), is to be attributed to Isoetion.
Geographical distribution: This community is very rare in Apulia, where it occurs in Iacorizzo doline, near Salice Salentino (Lecce). Brullo & Minissale 1998 Syn. Structure and ecology: Communities with acidophilus requirements, markedly more sciaphilous and hygrophilous than those of the Isoetion. They are localized on waterlogged soils of large hollows with waterproof surfaces, often represented by wood clearing, covered by a thick layer of clay-silt soil, often rich in a sandy component. In these stands, the hygrophilous microphytes are submerged by shallow rainwater sometimes until late spring. Mucina et al. (2016) Brullo & Minissale (1998). The two syntaxa are floristically and ecologically perfectly overlapping, since either way the associations referred to them (incl. Cicendietum filiformis) have the optimum at last spring to early summer occurring in the territories with temperate bioclimate and are characterized by a peculiar pool of species such as Centunculus minimus, Radiola linoides, Hypericum humifusum, Montia minor, Chaetonychia cymosa, etc.

Solenopsio laurentiae-Isoetetum todaroanae ass. nova hoc loco
Structure and ecology: This association is localized on waterlogged soils near sandy coast limitedly to small depressions flooded mainly during the winter period. Waterproof soils rich in sandy components characterise these stands. Floristically, the vegetation is dominated by Isoetes todaroana (= I. japygia), which usually grows with Solenopsis laurentia subsp. laurentia, Centunculs minimus, Anagallis parviflora, and several other species of the Isoeto-Nanojuncetea. Recently, an association with Isoetes todaroana has always been described in Apulia by Ernandes et al. (2017) as Pleurochaeto squarrosae-Isoetetum todaroanae surveyed by the authors on limestone outcrops limitedly to stands with non-stagnant runoff waters. On the whole, it seems a quite heterogeneous association in which moss communities are mixed with impoverished communities of the Isoeto-Nanojuncetea; consequently, it should be better studied and defined under the phytosociological aspect, basing on structurally more homogeneous relevés.

Solenopsidetum caespitosae ass. nova hoc loco
Geographical distribution: Basing on current data, this association occurs near Padula Mancina, located in the surroundings of Montesano Salentino (Lecce).  (Brullo et al., 2019). For its floristic set, the Poo jubatae-Isoetetum histricis shows close relations with the Junco capitati-Isoetetum histricis Br.-Bl. 1935 described from North Tunisia, but these two communities differ significantly for their ecology and floristic set. Previously, Ernandes et al. (2017) attributed the Apulian relevés characterized by Isoetes histrix, usually associated with I. sicula (sub I. inermis) to the Junco capitati-Isoetetum histricis, recognizing four subassociations. Most of these reléves that were carried out in the same our stands are somewhat impoverished floristically (probably due to excessive shading), and therefore their phytosociological arrangement is not clear at all, while the most complete are those referred to the subass. solenopsietum laurentiae, that fall very well in the association by us proposed. More recently, Pesaresi et al. (2018) emphasizing that the Apulian relevès published by Ernandes et al. (2017) can not be attributed to the Junco capitati-Isoetetum histricis, deem that they must be treated as a new association named Isoetetum siculaehistricis, recognizing all the four subassociations detected by the last authors. Unfortunately, the authors choose as holotype, among the relevès published by Ernandes et al. (2017) in Tab. 4, one of the poorest floristically in which almost all the most significant species of this plant community are missing. In particular, this relevé is the nomenclatural type of subass. isoetetosum siculae, that as already highlighted, is not informative under the phytosociological profile and, however, wholly different from the subass. solenopsietum laurentiae. The last syntaxon for its floristic set and ecological requirements must be considered as a distinct association represented by Poo jubatae-Isoetetum histricis, clearly belonging to Cicendio filiformis-Solenopsion laurentiae, likewise Junco capitati-Isoetetum histricis.

Radiolo linoidis-Solenopsidetum parvulae ass. nova hoc loco
Structure and ecology: This association was surveyed in a calcarentic rocky place near the sea, in small wet pools, within a garigue dominated by Erica forskalii. It occurs on silty-sandy soils flooded for short periods during the winter. Floristically, it is characterized by Solenopsis laurentia subsp. parvula, inconspicuous hygrophyte closely related to S. laurentia, from which it differs compared to the typical populations for its habit acaulescent, very reduced size and smaller flowers (see Appendix 2). Besides, this community is differentiated by Radiola linoides, a microphyte in Apulia noted only for this stands. Moreover, several elements of the Cicendio filiformis-Solenopsion laurentiae and Isoeto-Nanojuncetea are here quite frequent.
Geographical distribution: It was surveyed only in tiny pools along the rocky coast of Posticeddu (Brindisi).
Structure and ecology: This association is localized within the moist meadows dominated by Alopecurus rendlei, surrounding the vast wetland colonizing by plant communities of the Preslion cervinae. It occurs limitedly to the small pools, which are more depressed compared to the rest of the surface, remaining flooded for a longer period. Floristically this vegetation is characterized by Spergula arvensis, which grows together with Anagallis parviflora and several species of the Isoeto-Nanojuncetea. It is a quite rare association observed in inland flat stands at ca. 100 m altitude within large cultivated areas. Geographical distribution: It occurs in the wetland of Contrada Foresta (Cutrofiano). Brullo, Scelsi, Siracusa, Tomaselli 1998 (   from Mount Lauro in South Sicily. On the whole, the Apulian vegetation is very similar to that one from Sicily, although floristically much more impoverished.

1
Lythrum hyssopifolia 2 1 1 + 2 2 1 2 2 2 1 1 2 1 1 1 1 1 1 2 + . .    Troia & Greuter (2014 as synonym of I. gymnocarpa (Gennari) A. Braun, but according to Bagella et al. (2015), the latter is distributed in Sardinia, Corsica, Tuscany, and Balearic islands, while I. sicula must be considered a geographical vicariant in Sicily, South Italy, and Greece. Apart from this species, the plant community at issue is characterized by the high frequency of Agrostis pourretii, Moenchia erecta, and Ranunculus sardous, which grows together with other hygrophytes of the Isoeto-Nanojuncetea. In comparison to the previous association, it differs not only from its floristic set but also for the more marked mesophily.

Chamaemelo mixti-Agrostidetum pourretii ass. nova hoc loco
Structure and ecology: This association, very rare and quite poor floristically, occurs near the shoreline on sandy soils in retrodunal stands in contact with salt marshes. Species dominant of this vegetation is Agrostis pourretii, which constitutes ephemeral grasslands, where some peculiar therophytes are localized, such as Chamaemelum mixtum, Ranunculus trilobus, and Cornucopiae cucullatum, this last a rare species, occurring in Italy only in a few and very localized stands (Sciandrello & Tomaselli, 2011 Structure and ecology: Ephemeral vegetation localized in large wet hollows usually flooded until early summer, with soils mostly eutrophic or sub-eutrophic, often hypertrophic, usually well nitrified since used as pastures, more rarely oligo-mesotrophic. Floristically it is differentiated by the occurrence of species with summerautumn blooming, showing a prostrate and creeping habit.
Geographical distribution: This order is distributed in the Atlantic and central European territories, extending also to the Mediterranean area but limitedly to mesic habitats. Slavnić 1951 Syn Structure and ecology: Ephemeral vegetation occurring in large depressions subjected to long periods of submersion usually until early summer, characterized by well nitrified soils. In these habitats, flooded by eutrophic or hypertrophic water, prostrate-creeping species, often of large size, having a summer-autumnal blooming are frequent.
Structure and ecology: The association occurs in large depression submerged by rainwater for a long period, often until the early summer. The soil is slightly compacted and well nitrified by heavy grazing, that affects it until the summer. The vegetation is quite poor floristically and is dominated by some annual prostrate species, having their vegetative optimum in the summerautumnal period. In particular, the more frequent are Verbena supina, Coronopus squamatus, Damasonium alisma, and Paspalum distichum. From the literature (Brullo & Minissale, 1998) Structure and ecology: A very poor floristically plant community characterized by Heliotropium supinum and Heleochloa schoenoides, with more hygrophilous requirement compared to the previous association, was surveyed in other wetlands. Previously this association, belonging to Verbenion supinae too, was recorded from Spain (Rivas-Martinez et al., 2002) and Sicily (Brullo & Marcenò, 1974;Brullo et al., 2002;Sciandrello, 2009).
Geographical distribution: Currently, it was surveyed at Lo Specchione near Brindisi, but probably it occurs also in other Apulian wetlands.

Conclusions
The Isoeto-Nanojuncetea class in Apulia is represented by several associations, well differentiated from the floristic-structural and ecological point of view, which are taxonomically arranged in five alliances. This more or less marked autonomy of these associations is emphasized by the multivariate analysis carried out on all the phytosociological relevés.
The plant communities are localized in very peculiar and specialized temporary ponds and are usually characterized by rare and endangered species. As already highlighted by other authors (Ernandes & Marchiori, 2013;Bagella et al., 2016), this natural heritage, highly vulnerable and threatened by various anthropic pressures, sometimes deserves specific and urgent conservation strategies.
These Mediterranean wet habitats are characterized by a high level of biodiversity, regarding both plants and animals (many of which are often endemic), where it is possible to observe an alarming rate of loss and alteration due to their easy degradability.
According to the Habitats Directive, the Mediterranean temporary ponds are considered as habitats of Community Interest and placed in group 31 (Standing Waters). In particular, the associations belonging to Isoeto-Nanojuncetea, such as those recorded in Apulia, fall within the priority habitat 3170*, gathering all the orders and alliances of this class. These syntaxa, always in agreement with the Habitats Directive, are also included in the habitat 3120 or 3130, differentiating them only on ecological features. This treatment is quite ambiguous and not easy to interpret, although an attempt was made by Bagella et al. (2007), although questionable as well.
On the whole, the temporary ponds represent highly vulnerable habitats, mainly due to their fragile hydrologic regimes and to occupy small surfaces. In fact, many anthropic factors threaten the ecological balance of these wetlands (Zacharias et al., 2007), such as crop intensification, variations of land use, water mobilization, landfill, overgrazing, and fire.
The conservation of a network of temporary ponds with different hydroperiods depends primarily on shrewd environmental management, where the natural hydrologic regimes, and not intensive land use it could preserve its integrity for the behoof of the future generations.