Introduction

European freshwater habitats are often reported among habitats under strong human pressure, although they host an important proportion of global plant diversity (García-Girón et al. 2021). Main threats are related to enormous destruction and changes in water regimes (Keddy 2000), which are multiplied by ongoing climate change and plant invasions (Short et al. 2016; Reid et al. 2019). Many species growing in these habitats (e. g. in open waters, marshes, wet meadows, floodplain and swamp forests) are threatened. Their populations have declined sharply in recent decades, and several of the wetland species have become extremely rare or threatened with extinction.

In Central Europe, the genus Ranunculus L. provides a good opportunity to study the chorology and ecology of an abundant group of threatened freshwater species. This genus is a cosmopolitan and the largest in the family Ranunculaceae Juss., with a diversity of almost 600 species (Tamura 1995). The presence of 36 species, including sect. Batrachium, has been reported from Slovakia (Futák 1982). This species group also includes Ranunculus lingua as a typical wetland plant, which is threatened throughout Europe and globally (Bilz et al. 2011; https://www.iucnredlist.org/search?query=ranunculus%20lingua&searchType=species) and is evenly recorded in several national Plant Red Lists in Central Europe. For example, it is listed as critically threatened in the Czech Republic (Grulich 2012), vulnerable in Slovakia (Eliáš et al. 2015) and near threatened in Hungary (Király 2007). Several endangered vascular plants with a clear vegetation preference for wetland habitats have recently been studied in Slovakia (e. g. Beckmannia eruciformis – Dítě et al. 2011; Ludwigia palustris – Dítě et al. 2017; Calla palustris – Dudáš et al. 2021), but the distribution and vegetation patterns of the greater spearwort (R. lingua) have not yet been critically reviewed.

Ranunculus lingua L. (Ranunculaceae, sect. Lingua) is an Euro-Siberian species distributed in western part of the Palearctic region, mainly throughout the temperate zone of Eurasia, less frequently in boreal and northern part of the Mediterranean zones. It occurs from northern Spain and Great Britain, followed by France, Central European countries and Scandinavia to the Balkan Peninsula, extending eastwards to the Baltic States, Belarus, Ukraine and European Russia, including south-western and southern Siberia (Meusel et al. 1965; Jalas and Suominen 1989; Hörandl 2022). The species is absent from most Mediterranean inland areas and islands. In Central Europe the majority of localities are situated along large lowland rivers. R. lingua is scattered to rare in Hungary (Bartha et al. 2015), Czech Republic (Křísa 1988) and Slovakia (Futák 1982), but relatively common in Poland (Zając and Zając 2001). This herb species prefers meso-eutrophic wetland sites, such as channel beds, muddy depressions, semi-saline swamps, marshes, mires and ponds. It also thrives in submerged habitats with shallow water that may partially dry out in late spring or summer (Casper and Krausch 2008). It is classified as a helophyte with its overwintering buds submerged below the sediment surface (Johansson and Nilsson 1993).

In Slovakia, species Ranunculus lingua seems to be distributed throughout the country, but with expected regional discrepancies. Historical observations (Futák 1982) suggest that the species was more common in wetland habitats in the southern areas, while most of the scattered records in other areas were associated rather with minerotrophic mires or swamp forests. Contrary to this distribution pattern, vegetation characteristics of R. lingua have been almost completely missing. Therefore, we aimed to revise and summarise the chorology with insight into temporal trend and vegetation affinity for the species R. lingua in Slovakia.

Materials and methods

Revision of herbarium specimens in Central European public herbaria (BP, BRA, BRNM, BRNU, CL, EGR, HLO, HNTS, HUM, KO, LTM, MMI, MPS, NI, OL, OLM, PMK, POP, PR, PRC, SAV, SLO, SMBB, SNV, TM, VSMU, ZAM and ZV) accompanied by intensive field research was carried out by the authors in the years 2018–2022 (only some of the older localities were revised). Especially, older mentioned localities without any habitats suitable for Ranunculus lingua verified by authors of the paper in the field and/or the authors of the relevant published papers were signed as destroyed (see also Fig. 1).

Fig. 1
figure 1

Distribution of Ranunculus lingua in Slovakia. Black triangles indicate extinct populations or destroyed localities, and dots overall distribution. International codes of countries are shown. Coloured background corresponds to phytogeographical division of Slovakia according to Futák (1984)

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The herbarium acronyms followed Thiers (2023 +) and small local museum collections were unified according to Vozárová and Sutorý (2001). Floristic records were also obtained from the JACQ – Virtual herbaria database (www.jacq.org), published literature sources and relevant unpublished works or manuscripts (mainly stored at the Institute of Botany, Plant Science and Biodiversity Center, Slovak Academy of Sciences, Bratislava, Slovakia). All these data sources were used to prepare the distribution map of the species in the program ArcGis, version 9.2. Historical and recent records were arranged according to the phytogeographical affiliation proposed by Futák (1984). They were also assigned to the quadrants of the Central European Flora Mapping grid (CEFMG) template (Niklfeld 1971; Jasičová and Zahradníková 1976).

List of individual localities taken from herbarium specimens includes the name of the collector, the year of collection and the herbarium acronym in parentheses. References for published records are given in abbreviated form, i.e. they comprise author of the publication, journal abbreviation and volume, page with R. lingua record and year of publication. For unpublished field records, the year of finding is followed by the name(s) of the author(s). Locality notes were translated, with a few exceptions where historical names of localities are given in their original form, indicated by parentheses (see Appendix).

Phytosociological relevés with the occurrence of R. lingua in Slovakia were obtained from the Slovak Vegetation Database (code EU-SK-001 in the Global Index of Vegetation-Plot Databases; Šibík 2012) and completed by one original plot. We compiled a total of 36 vegetation plots stored in the Turboveg database (Hennekens and Schaminée 2001), which were in the next step exported to the Juice program (Tichý 2002). Species taxonomy was unified using the concept of broadly defined plant taxa. Specifically, we used only three aggregate taxa, namely Eleocharis palustris agg. (E. palustris, E. uniglumis), Galium palustre s. lat. (G. elongatum, G. palustre) and Valeriana dioica agg. (V. dioica, V. simplicifolia). Bryophytes were excluded from the dataset because they were identified in only a part of the relevés. Numerical classification was performed with species merged into a single layer using the modified TWINSPAN algorithm (Roleček et al. 2009) with settings of four pseudospecies cut levels (0%, 5%, 25% and 50%) and total inertia as a measure of cluster heterogeneity. The differential species of each cluster were determined using frequency and fidelity thresholds (Φ – phi coefficient; Chytrý et al. 2002). The Fisher’s exact test (p < 0.05) was used to eliminate species with a non-significant occurrence in a given cluster (Tichý and Chytrý 2006). Thus, differential species were defined as species that simultaneously had frequency ≥ 20%, phi coefficient ≥ 0.30 and difference in frequencies between clusters ≥ 20%. If a particular species was constant (reached frequency > 50%) in two or more clusters, it was not accepted as differential.

Nomenclature of plants and higher syntaxa follows checklists of Marhlod and Hindák (1998) and Mucina et al. (2016), respectively. Association names of plant communities are mentioned according to Slovak vegetation overviews (Valachovič 2001; Valachovič et al. 2021), and we also adopt the contemporary outcomes of European vegetation revisions (Douda et al. 2016; Landucci et al. 2020).

Results

Distribution of R. lingua in Slovakia

Localities of R. lingua in Slovakia are concentrated in the area of the Pannonian flora region, with distribution centres situated in the western, south-western and south-eastern parts of the country. They include mainly lowland areas (e. g. Záhorská, Podunajská and Východoslovenská nížina Lowlands) with some outposts in the northern Carpathian regions. Here, the species is rare and several populations have become extinct or suitable habitats for the species have changed (Fig. 1). We recorded R. lingua in 19 phytogeographical districts of Slovakia (out of 31 in total), including 5 in the Pannonian (Pannonicum) and 14 in the Western Carpathian (Carpaticum) biogeographical regions (Fig. 1, see Appendix for details).

Although the oldest record of R. lingua was reported by G. Reuss in the half of the nineteenth century, the increasing number of new localities started in the 1920s and peaked in period of the 1950s-1970s. The destroyed suitable habitats for existence of R. lingua created almost 16% of all CEFMG with the species distribution (Fig. 2).

Fig. 2
figure 2

Number of data records along temporal axis with quarterly periods

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Vegetation characteristics of R. lingua

Numerical classification using the Twinspan algorithm split phytosociological relevés with the occurrence of R. lingua into forest and non-forest wetlands (Table 1). Forest vegetation was mainly represented by willow and alder carrs (phytosociological classes Franguletea and Alnetea glutinosae), but species was also occasionally found in willow floodplain forests (Alno glutinosae-Populetea albae). Non-forest vegetation corresponded to marshy plant communities (Phragmito-Magnocaricetea), exceptionally to ephemeral wetland vegetation of exposed beds (Isoëto-Nanojuncetea). The most frequent co-occurring species were Galium palustre s. lat. (in 72% of the relevés), Lysimachia vulgaris (69%), Lycopus europaeus (61%) and Lythrum salicaria (61%), followed by Equisetum fluviatile (44%), Iris pseudacorus (42%) and Carex elata (42%). These are typical species of marshes and swamps dominated by willows and alders.

Table 1 Shortened synoptic table of plant communities with occurrence 412 of Ranunculus lingua in Slovakia is shown. Relative frequency of the species in given cluster with median cover values in upper index (cover values only in cluster 7) are presented. They are displayed in bold only for differential species of each cluster
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The first cluster of relevés grouped flooded marshes with a constant presence of aquatic plants. This vegetation was syntaxonomically interpreted as the Phragmition communis alliance (associations Glycerio-Sparganietum neglecti and Typhetum angustifoliae). Mesotrophic stands of the Magnocaricion elatae alliance (as. Caricetum diandrae, Menyathetum trifoliatae and Caricetum acitiformi-paniculatae) were merged in the second cluster. The third cluster contained a wide range of typical eutrophic marsh communities dominated mainly by graminoids (i.e. tall sedges and grasses) of the alliances Phragmition communis (as. Glycerio-Sparganietum neglecti and Glycerietum maximae), Magnocaricion elatae (as. Caricetum elatae and Carici elatae-Calamagrostietum canescentis) and Magnocaricion gracilis (as. Caricetum riparae, Caricetum vesicaria and Caricetum gracilis). Vegetation of the exposed bottoms belonging to the Nanocyperion alliance was classified in the last 7th cluster (Table 1). Three clusters (no. 4–6, Table 1) were distinguished for different alliances of forest vegetation, namely willow floodplain forests of the Salicion albae (as. Salicetum fragilis; cluster 4), alder and willow swamps of the Alnion glutinosae (as. Carici elongatae-Alnetum glutinosae and Carici acutiformis-Alnetum glutinosae; clusters 5 and 6) and the Salicion cinereae (as. Salicetum pentandro-auritae; cluster 5). Early successional stages of swamp forests with the presence of numerous wet meadow plants were also found especially in cluster 6 (Table 1).

Discussion

The initial chorology of the species Ranunculus lingua in Slovakia reported by Futák (1982) is now outdated, as several localities were mentioned as historical at that time. Moreover, Futák already suggested that synergistic effect of various anthropogenic activities (e. g. drainage or gradual urbanisation of large areas) had induced pronounced environmental changes and destroyed many of the original populations. Expert revision of both herbarium specimens and available published data allowed us to update the distribution pattern of this species in Slovakia.

The first record of R. lingua reported by Reuss (1853) near Prešov is without a precise localisation or habitat description, similarly as the herbarium specimen collected by F.A. Hazslinszky (deposited in BP), whose botanical research in this region was probably performed in the second half of the nineteenth century. Revision of the specimens in other public herbaria suggests that this historical locality (localities) may correspond either to swamps near Šalgovík (specimens in SLO and MPS) or to Fulianka (specimen in SAV). However, our current floristic research has not proved the species occurrence there.

Our results indicate that R. lingua has not been observed in several mountainous regions of the Western Carpathians (e. g. Strážovské vrchy Mts, Poľana Mts, Lúčanská Fatra Mt., Pieniny Mts, Spišské vrchy Mts, the Čergov Mts) for many decades, in some cases for more than a century (Appendix), and species is therefore considered as regionally extinct. This could be explained mainly by habitat destruction or at least by severe modifications in environmental conditions (changes of water regimé caused especially by human or secondary succession). A similar situation has been recognized in other hilly and mountainous areas, such as the Orava region, the Biele Karpaty Mts, the Šarišská vrchovina upland and in the ponds near the village of Hrhov in the Slovenský kras karst. Although no original records have been newly found here, there are several suitable habitats with optimal ecological conditions where the species could still survive today. On the other hand, most of the historical data in the Podunajská nížina Lowland overlaps with the recent distribution of the species. The current localities were recorded particularly along swamps, channels and river oxbows of the Dunaj and Malý Dunaj or along the lower course of the Váh and Ipeľ rivers. Species is very scattered to rare in the lowlands of Borská nížina (Májeková and Zaliberová 2006) and Východoslovenská nížina. Outside the lowlands, R. lingua recently occurs only in localities situated close to the village of Machulince in western Slovakia, near the village of Polomka in central Slovakia (Fig. 3) and near Poprad in northern Slovakia (for details see list of localities and Fig. 1). It is considered to be rare in north-eastern Slovakia because several populations have became extinct and the last isolated occurrence in the Nature reserve Čertižnianské lúky has been confirmed in 2004 (see Appendix). For comparison, species is also rare in the adjacent hilly areas of south-eastern Poland, but the number of populations increases northwards in the lowland areas (Zając and Zając 2001).

Fig. 3
figure 3

Ranunculus lingua near the village of Strážne (left; author Daniel Dítě, 6.7.2009) and Polomka (right; author Martin Veverka, 1.7.2022)

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The number of records has also been rapidly decreased in south-eastern Slovakia (mainly in alluvial pools of the Bodrog and Latorica rivers) over last 60 years, probably due to extensive melioration and drainage of the area (Bella 1971; Terek and Matas 1983). Several populations of R. lingua still exist near the village of Strážne (south-eastern of Slovakia) in a complex of terrain depressions between sandy dunes used for grazing and on the banks of channels (Fig. 3). This unique grazed wetland site, with the largest recent population of R. lingua, also hosts other rare and endangered species such as Beckmannia eruciformis (Dítě et al. 2011) or Cirsium brachycephalum (Mártonfi 2014). Along channels R. lingua grows in wetland vegetation dominated by tall-sedges and willow shrubs together with typical marsh and wet meadow species such as Calystegia sepium, Glyceria maxima, Lythrum salicaria, Scutellaria galericulata, Schoenoplectus lacustris, and Stachys palustris.

The species is a popular ornamental herb planted locally in small ponds. It can survive there for a long time (e. g. Kochjarová et al. 2013) and has the potential to spread to natural aquatic and wetland habitats, mainly if they are hydrologically connected. However, this accidental introduction pathway has not been found in Slovakia.

Futák (1982) provided only a brief insight into vegetation affinity of R. lingua, based on his empirical (expert-based) knowledge. It was listed as a characteristic species mainly in the alliances Phragmition communis and Magnocaricion elatae. Our vegetation analyses showed that R. lingua occurs in a wide range of wetland habitats, mainly floodplain forests, alder and willow carrs of the classes Franguletea, Alnetea glutinosae, Alno glutinosae-Populetea albae and freshwater treeless habitats of the class Phragmito-Magnocaricetea. They are characterised by spring or early summer floods followed by water level fluctuations with a relatively long-term presence of water below the soil surface. These intra-annual variations in water levels have an important effect on the growth and reproduction of R. lingua (e. g. Johansson 1993; Rybka and Duchoslav 2007) and on the variability in species composition of plant communities. A similar vegetation niche of the species has also been reported from other Central European regions in Poland and Hungary (e. g. Solińska-Górnicka 1987; Matuszkiewicz 2008; Lóczy 2019). However, countries with a higher number of localities showed a wider range of habitats. For example, R. lingua is able to grow in wet meadows, oligotrophic lakes and pools, slowly flowing rivers, large shlallow lakes and mires as well (Wassen et al. 1995; Szoszkiewicz et al. 2010; Lukács et al. 2015; Chytrý et al. 2021). The species has been frequently observed throughout Europe in vegetation dominated by tall-sedges and grasses of the Magnocaricetalia order (Appendix S7 in Landucci et al. 2020), but also thrives in alder carrs (e. g. Solińska-Górnicka 1987). Several plant communities with R. lingua occurrence reported in other European countries are rare (e. g. Caricetum diandrae) or recently unlisted (Menyathetum trifoliatae) in Slovakia (Valachovič, 2001) due to strong changes in the lowland landscape in last decades.