The lichens of the Majella National Park (Central Italy): an annotated checklist

Abstract The botanical exploration of the Majella National Park has a long tradition dating back to the eighteenth century. However, the lichen biota of this area is still poorly investigated. To provide a baseline for future investigations, in this annotated checklist, we summarised all available information on the occurrence of lichens in the Majella National Park, retrieved from previous literature, herbarium material and original data produced by recent research. The checklist includes 342 infrageneric taxa. However, seven taxa are considered as dubious, thus setting the number of accepted taxa at 335, i.e. 45.8% of those currently known to occur in the Abruzzo Region. This checklist provides a baseline of the lichens known to occur in the Majella National Park, highlighting the potential of this area as a hotspot of lichen biodiversity, especially from a biogeographical point of view as indicated by the occurrence of several arctic-alpine species that form disjunct populations in the summit area of the massif.


Introduction
The botanical exploration of the Majella National Park has a long tradition dating back to the eighteenth century, which has provided the basis for the compilation of a recent checklist of vascular plants including 2286 infrageneric taxa (Conti et al. 2019). This massif clearly is a hotspot of plant diversity due to the interaction of physical, climatic and biogeographic factors. In particular, the flora of high-elevation habitats consists of many endemic taxa of high phytogeographic relevance.
On the other hand, the lichen biota of this area is still poorly investigated. Historical data are scanty, the main contribution being that by Nimis and Tretiach (1999), who carried out intensive lichen collections along the eastern part of the Italian peninsula. These authors collected several specimens, currently stored in the TSB herbarium, in at least five localities distributed along a steep elevational gradient, from 500 to 2500 m, in the Majella National Park. Ten years later, Cucchi et al. (2009) studied the microtopography of carbonatic rocks, reporting several endolithic taxa. Overall, these collections revealed several interesting species that were either new to the Abruzzo region or indicative of the biogeographic importance of the Majella massif also for lichens. For example, several arctic-alpine lichens occur there in small and disjunct areas at the southernmost limit of their European distribution, the nearest populations being in the Alps (Nimis 2016).
In 2017, a scientific collaboration started between the administration of the Majella National Park (with its botanical office) and the University of Bologna, under the project "Lichen biodiversity in the Majella National Park", with the aim of contributing to fill this knowledge gap. Besides pure floristic explorations (e.g. Nascimbene et al. 2019), the research project also included ecological investigations, mainly focused on high elevation areas, for example, a lichen survey on the four GLORIA summits ) and along an elevational transect across the whole main ridge of the massif (Di Nuzzo et al. 2021).
To provide a baseline for future investigations, in this annotated checklist, we have summarised all available information on the occurrence of lichens in the Majella National Park, retrieved from previous literature, herbarium material and original data produced by our research. In this checklist, very few lichenicolous fungi are included. To be treated exhaustively, this component would require specific investigations.

Study area
The Majella National Park (MNP) is located in the central Apennines, Italy, and was established in 1995 by National Law 1991, n. 394, to preserve, protect and enhance the high value of the inherent natural, historical and cultural resources of the area. The Park consists mainly of carbonate mountains, separated by valleys and karst high plateaus, with a broad altitudinal range (130-2,793 m a.s.l.). The Majella massif has more than 60 peaks, with half of them rising above 2,000 m and includes the second highest peak in the Apennines, Mount Amaro (2,793 m). From a bioclimatic point of view, the study area is included in the alpine biogeographical region (Cervellini et al. 2020) and the climate corresponds to the subalpine-alpine humid type as far as the lower summit is concerned, whereas the other summits belong to the alpine humid type (Blasi et al. 2005). The Park's territories are part of the Natura 2000 network. The boundaries coincide with a Special Protection Area (SPA) for the conservation of wild birds (established by the Birds Directive 79/409/EEC). Furthermore, within the Park, there are four Special Areas of Conservation (SAC), established by the Habitats Directive 92/43/EEC (Di Cecco et al. 2020).

The data
Occurrence data were retrieved from multiple sources, for a total of 1625 records: 1) critical evaluation of literature records (463 records from 10 publications); 2) 217 records stored in on-line available herbaria, mainly from TSB (Herbarium of the University of Trieste); 3) reliable field observations related to our research project (e.g. only in the case of easily-identifiable species) recorded between 2017 and 2019 (100 records); 4) 845 herbarium records (personal herbarium of JN and GG) related to our research project collected between 2017 and 2019.
The specimens collected during our project were identified in the laboratory using a dissecting and a compound microscope. Routine chemical spot tests were performed for most specimens. The identification of sterile crustose lichens (e.g. Lepraria-species) was based on standardised thin-layer chromatography (TLC), following the protocols of Orange et al. (2001).
Lichen nomenclature, as well as synonymisation of old records, follow ITALIC 6.0 -The information system on Italian Lichens (Nimis and Martellos 2020), which is mainly based on the checklist of the Italian lichens by Nimis (2016). This source was used also for retrieving information on biological traits, ecological requirements and geographic distribution for each taxon.
Taxa are listed alphabetically. For each taxon, the accepted name, all available records, the altitudinal distribution, habitat preference and/or substrate are reported, whenever information is available. A short note (on ecology, distribution and/or taxonomy) is associated with each noteworthy taxon (e.g. taxa which are new to the region and/or of particular biogeographic or conservation importance). Dubious records are reported at the end of the checklist. For each record, a critical note accounting for the "dubious status" is reported.
3) main reproductive strategies: 257 taxa (76.8%) mainly disperse by sexual reproduction, forming ascospores in apothecia or perithecia, while 77 taxa (23.2%) disperse by asexual reproduction (22 by means of isidia or isidia-like structures, 47 by means of soredia or soredia-like structures and seven mainly by means of thallus fragmentation The record of the steppic lichen Circinaria hispida provides a connection between the main area of distribution of this taxon (Eastern Europe and Central Asia) and its scattered Western European populations (Northern Italy, Spain).

Calogaya lobulata (Flörke) Arup, Frödén & Søchting
Majella (C73). -The historical record was not confirmed recently, but it is considered as reliable since the ecological requirements of this species (Nimis 2016) occur within the study area. This old record is the only one from the Majella massif. The other records from Abruzzo were collected elsewhere (Nimis 2016). The species is included in the Italian Red List of epiphytic lichens as "vulnerable" (Nascimbene et al. 2013).

Calogaya pusilla (A. Massal.) Arup, Frödén & Søchting
Majella (C73; J74). -The historical records were not confirmed recently, but they are considered as reliable, since this is a widespread species (Nimis 2016).  Nimis and Tretiach (1999), but later Nimis (in Nimis and Martellos 2020) revised the material, which proved to belong to C. rouxii. Candelaria concolor (Dicks.) Stein Majella (C73; J74). -The historical records were not confirmed recently, but they are considered as reliable, since this is a very widespread species (Nimis 2016), which is probably common in the study area at low elevations. -This species was previously reported from Abruzzo, as C. unilocularis, only from the Gran Sasso massif by Nimis and Tretiach (1999).  (Hafellner et al. 2004;Roux et al. 2017). This is a species typical of cold steppes and deserts which occurs in Eastern Europe, Near Asia, Central Asia and North America; it is found also in Juniperus steppes of Central Spain and the scattered occurrences in Italy, France and Greece represent natural connections between the two European disjunctions (Hafellner et al. 2004). Roccacaramanico (NT99;

Clauzadea monticola (Schaer.) Hafellner & Bellem.
of the Apennines (Nimis 2016) and was reported previously from Abruzzo only by Recchia and Villa (1996).   Hertel (1967) from the Majella and the Gran Sasso massifs, where it was recorded also by Nimis and Tretiach (1999). it was previously reported from Abruzzo only from the Gran Sasso massif by Nimis and Tretiach (1999).   Lecanora varia (Hoffm.) Ach. Majella (C73;J74). This old record was not confirmed by recent surveys, but it can be considered reliable since this cool-temperate to circumboreal-montane lichen is common on hard lignum in upland areas, including Mediterranean mountains (Nimis 2016).   (Nimis and Tretiach 1999). Those from Majella are the southernmost records of this taxon for Italy (Nimis 2016).

Opegrapha rupestris Pers.
Majella (C73; J74). -The historical records were not confirmed recently, but they are considered as reliable, since this is a widespread species. Lichenicolous in various verrucarialean crustose lichens (Nimis 2016). Majella (C73); Campo di Giove (J74). -This is a silicicolous, arctic-alpine circumpolar lichen (Nimis 2016) that likely meets its substrate requirements in the Majella massif on flint limestone. The southernmost records in Italy are those of Calabria (Nimis 2016). Parmelia saxatilis (L.) Ach. Majella (C73); S. Antonio (J74). -The historical records were not confirmed recently, but they are considered as reliable, since this is a widespread species (Nimis 2016). However, different cryptic species may occur in the group of P. saxatilis (e.g. Molina et al. 2004) and further research is required to clarify which of them occurs in the study area. Parmeliella triptophylla (Ach.) Müll. Arg. Majella (C73). -The historical record was not confirmed recently, but it is considered as reliable, since the ecological conditions required by this species (Nimis 2016) occur within the study area. It is included in the Italian Red List of epiphytic lichens as "nearthreatened" (Nascimbene et al. 2013).  Roccacaramanico (NT99;. -In the montane belt (1000 m: NT99; TSB). On calcareous rock (TSB).

Sarcogyne regularis
Usnea barbata (L.) F.H. Wigg. Majella (C73). -Most Italian records of the genus Usnea would require accurate revision and this historical record was not confirmed recently. However, we considered it as reliable, since the ecological conditions required by this species (Nimis 2016) occur within the study area.
Usnea dasopoga (Ach.) Nyl. Bosco di Pacentro (J74). -Most Italian records of the genus Usnea would require accurate revision, and this historical record was not confirmed recently. However, we considered it as reliable, since the ecological conditions required by this species (Nimis 2016) occur within the study area.

Variospora aurantia (Pers.) Arup, Frödén & Søchting
Majella (C73). -The historical record was not confirmed recently, but is considered as reliable, since this is a widespread species (Nimis 2016). -This is a coastal species occurring on rocks at the interface between the littoral and the mesic supralittoral belts (Nimis 2016) whose occurrence in the study area is very dubious. The record was reported by Jatta under the name Lichina elisabethae A. Massal.

Rinodina oxydata (A. Massal.) A. Massal.
Valle dell'Orfento (J74). -This is a silicicolus taxon whose occurrence in the Majella massif would be related to flint limestoine. Since this would be the only record for Abruzzo, it requires confirmation.

Discussion
This checklist provides a baseline of the lichens known to occur in the Majella National Park, highlighting the potential of this area as a hotspot of lichen biodiversity, especially from a biogeographical point of view. On one hand, the high number of regionally-new taxa discovered during our recent investigations suggests that further research is needed to reach a more exhaustive picture of the lichen biota of Abruzzo, as well as of the Majella massif. In particular, a more intensive collection in rocky and forest habitats, as well as in high elevation ranges, is likely to produce a relevant increase in the number of species.
On the other hand, the occurence of many arctic-alpine taxa (see Nimis 1997;Nimis and Tretiach 1995) that reach here their southernmost Italian or European distribution limit and the occurence of steppic chorotypes, as in the case of Circinaria hispida, confirm the phytogeographical peculiarity of this area also for lichens (see Conti et al. 2019 for vascular plants; Nimis 2016 for lichens). In the core of the Mediterranean Region, small, disjunct populations of artic-alpine taxa that are disjunct from those of the Alps are currently restricted to the highest 200 m of the Majella massif. In a global change perspective, this cold-adapted, disjunct component of the lichen biota is strongly exposed to the impact of warming conditions, as in the emblematic case of Allocetraria madreporiformis whose main local populations almost exclusively occur within Salix retusa islands in the Macellaro summit. The past establishment and cur-rent persistence of these cold-adapted taxa are likely related to the great extension of the high altitude area characterised by vast plateaus that may provide microrefugia (e.g. small-scale cold refugia) suitable for these small-sized organisms (Conti et al. 2019).
In addition, the epiphytic lichen biota is noteworthy, including several species of conservation concern that are Red-listed in Italy (Nascimbene et al. 2013; a national Red List is currently available only for epiphytic species). This indicates that the forests of the Majella National Park effectively contribute to the conservation of endangered epiphytic species of the Italian lichen biota. The best conserved part of the "Bosco di S. Antonio" forest is an emblematic example of this situation, hosting species sensitive to human disturbance as Lobaria pulmonaria or rare calicioid lichens .