Petalophyllum ralfsii (Wilson) Nees et Gottsche in Calabria: distribution, ecology and conservation

https://orcid.org/0000-0002-7533-6057 � Abstract: This paper reports data on distribution of Petalophyllum ralfsii in Calabria (S Italy). Investigations conducted from 2016 to 2019 permitted to outline an updated and accurate overview on the number and size of the populations of the species in the region. New findings were recorded, while some known locations were not confirmed. The size of each population was measured by direct counting of thalli or by sampling with plots, enabling to have a reliable estimate of the species density. Analysis of data gives also important information on the ecology and dynamism of


Introduction
After the discovery of a new population of Petalophyllum ralfsii (Wilson) Nees & Gottsche in Calabria, an investigation was launched in 2016 to verify known populations and apply methods for quantifying density. In the area of the middle Valle of Crati River, small populations were already known, with dozens of individuals. The new site, which by number of individuals could represent the largest population in Italy, has been the subject of various inspections in which an attempt has been made to develop an effective and expeditious monitoring methodology. Monitoring activities have been extended to all the populations known in Calabria, located largely along the Crati Valley. The presence of the species elsewhere is more sporadic, in particular on the Tyrrhenian coast (Capo Suvero), the Ionian coast (Foce del Crati) and in the surroundings of Crotone, where however the presence has not been confirmed recently.
Petalophyllum ralfsii is a thallose liverwort, included in Appendix I of Bern Convention of 1991 and listed on Annex II of the EU Habitats Directive. It has a light green thallus 5-10 mm long, with thin lateral wings and carinated rib, swelled at the end, in old thalli covered by rhizoids. Sporophytes ripe in March-April. It develops in springs and disappears in summer when it survives the aridity producing spores, remaining dominant till next spring. Also, it has a rhizome-like subterranean axis which becomes tuberous at the apex of mature plants, and which enables it to withstand long periods of desiccation (Paton, 1999).
The species occurs on wet and sandy places, on the shore of coastal ponds, in the rainiest periods, from the level of the sea up to 300 m of altitude. It is an Oceanic-Mediterranean species, distributed in the Mediterranean Region extending northwards along the Atlantic coast (Campbell et al., 2015). Populations of southern USA were recently referred to a distinct species, P. americanum C. H. Ford & Crand.-Stot. (Crandall-Stotler et al., 2002).
In Europe P. ralfsii is not very widely distributed. It has discontinuous populations in North Africa, Spain (in the Balearic Islands), Portugal, Greece (including Crete), Italy (including Sicily and Sardinia), and Turkey, extending northwards along the Atlantic coast to Britain and Ireland (Söderström et al., 2002;Ros et al., 2007).
A review of its distribution in Italy is presented in Aleffi (2008) who reports it in few localities of Tuscany, Calabria, Sicily and Sardinia (11 localities total). In Calabria only two sites are indicated: Capo Suvero and Campagnano (Aleffi & Puntillo, 1998).
Last investigations in Calabria allow to have a more updated and exhaustive scheme of distribution in the Region, showing a very changeable situation, with new populations recording in dynamic environments and frequent disappearance of others. A short term monitoring system is necessary for a correct interpretation of population dynamism and trends of this so interesting species.

Material and methods
Distribution data in Calabria come mostly from investigations and collections started in 80s by D. Puntillo. Specimens kept in the Herbarium of Museum of Natural History of Calabria and Botanic Garden (CLU) have been used to outline the preliminary distribution map of the species in the region.
New field surveys were carried out from 2016 to 2019 in order to verify known populations, extending investigations to potential sites looking for new findings.
Phytosociological relevés were carried out in order to determine syntaxa and Natura 2000 habitat in which the species occurs.
Monitoring methods applied for the species in other countries (Campbell et all., 2015) have been evaluated as well as methodology proposed in Italy (Ercole et al., 2016), in order to comply with commitments arising from article 17 of Habitat Directive, but above all to obtain useful information about trend and dynamism of populations in South Italy, the effective impact of human activities and the real conservation status of the species.
For every population, the covered area was calculated in m 2 . When possible, for small populations, number of individuals were estimated by coverage percentage and direct counting of single thalli. For larger populations counting was carried out in small plots of 0,5 m x 0,5 m, with a grid of 0,1 m x 0,1 m. The area covered by the population (m 2 ) was multiplied by the mean number of thalli/m 2 .

Results and discussion
In Calabria, Petalophyllum ralfsii is recorded in three main areas: Neto River, close to Cotronei in the province of Crotone; on the Thyrrenian coast, north of Cape Suvero (Falerna, CS) and in the Crati Valley, from Cosenza to the Crati River mouth. Investigations in these three areas permit to update distribution data as shown in Table 1.
Population of Neto river (PET_CAL9), recorded in 1997, was not confirmed, and its disappearance is probable because of drastic changes in the location. The station of Falerna (PET-CAL4) is confirmed, but with a very small population (ca. 40 thalli). The Crati Valley (Table 2)  Substratum is characterised by alluvial soils, rich in sand and very wet in winter and spring. Only the populations in Cape Suvero (PET_CAL4) and Crati River mouth (PET_CAL12) are located on the dunal system, on depressions with compact sand, from 40 to 90 m far from shoreline.
All locations are in a strong dynamic ecological contest, due not only to the characteristics of ecosystems (coastal dunes and river banks), but also to human activities.
The population found in 2016 along Settimo creek (PET_CAL1) is probably the largest one in Italy, with a covered area of 2590 m 2 and a density that reaches 700 thalli per m 2 . includes typical euhemerophilous pioneer bryophyte vegetation on temporary dry and dry loamy soils in the nemoral and boreal zones (Ercole et al., 2016;Mucina et al. 2016).
Nordic community of Ireland and Great Britain are referred to "2190 Humid Dune Slack", listed on Annex I of the EU Habitats Directive. This habitat type has re-cently been ruled out from Italy, so coastal dune depressions are referred to other habitat types. In Ercole et al. 2016 Petalophyllum ralfsii is not referred to specific habitat in Council Directive 92/43/EEC.
In the relevé in Crati Valley characteristic species of Isoëto-Nanojuncetea are very scarce or absent, but there is a significant group of bryophytes of Psoretea   (Table 3). Distribution data of P. ralfsii in Italy have recently increased (Cogoni et al., 2006;Provenzano et al., 2011) because of more attention paid to this species since its inclusion in Annex II of Habitat Directive. Therefore, it's not easy to understand its real demographic trends at long term and there is no evidence of a clear decline also because of the scarcity of previous data. Moreover, the dynamism of habitats and the ecology of the species are at the base of strong fluctuations in population density.
In any case it is evident that P. ralfsii in Mediterranean area is not exclusive of coastal habitats (Puntillo, 2004;Sim-Sim et al., 2000;Cogoni et al., 2006;Provenzano et al., 2011), and in the inner areas it finds environmental conditions that are dynamically similar to a dunal system, preferring river banks and alluvial soils. By a diachronic comparison of orthophotos it is evident that the richest populations of Crati valley colonised former sand pits, where the species is advant- aged by the scarcity of vascular flora (Fig. 3). A similar situation has been verified for other populations too.
The progressive stabilisation of substratum and the evolution of vegetation, with increasing of perennial herbs and shrubs, can determine a negative trend leading to the total disappearance of the population. In PET-_CAL6, for example, the population is very scattered probably because of gradual evolution of vegetation.
The species occurs on sandy and silty soils colonising open areas without arboreal and shrub vegetation. However, in many sites it was observed that thallus growing under grass heads and small shrubs are more luxuriant. Also, in the largest population (PET-CAL1) the species seems to tolerate the coverage of the falling down poplar leaves, where thallus is favoured by the persistence of humidity conditions. At the Crati River mouth, all micro-populations stand under Ephedra distachya shrubs. It is likely that on the Atlantic coasts Petalophyllum can live in drier environments, directly on the dunes, but with a more humid general climate. Whereas, in Mediterranean areas it needs small depressions with greater water stagnation where it finds favourite ecological conditions and, moreover, doesn't find competition with other bryophytes (Walter & Straka 1970).
It is a fact that all stands of P. ralfsii in Calabria are localised in areas subject to rapid and drastic transformations, often very close to urban agglomerations. For this, in spite of its pioneer character and new findings, it should continue to be considered a threatened species.
Definition of the range of the species is very difficult because of its ecology that in Mediterranean area is not confined to dunal habitats like in Northern Europe but colonises alluvial soils along river valleys.
In order to compensate costs and benefits, an optimised monitoring programme could be based on a rapid assessment of known populations, their size and main pressure factors. Simultaneously, small representative permanent areas, can be chosen for a detailed demographic analysis in order to interpret fluctuations and relations with ecological conditions and vegetation evolution.   monitoring activities in 2018-2019 were conducted under the Natura 2000 monitoring programme in Calabria (funded by POR FESR CALABRIA 2014/2020, action 6.5.A1).