Notes on Caloplaca lucifuga (Teloschistales, Ascomycota) in Poland

The current knowledge on the occurrence of Caloplaca lucifuga , a rare lichen with an inconspicuous crustose sorediate thallus, is discussed. Both previous and new localities are presented. The most important data on the ecology and general distribution of the species are given. Diagnostic characters related to the morphology, anatomy and chemistry of C. lucifuga that help to differentiate it from similar species are described.


INTRODUCTION
Caloplaca lucifuga belongs to a group of crustose, sterile sorediate lichens that are relatively poorly known in Poland (Nowak, Tobolewski 1975;Śliwa, Tønsberg 1995;Śliwa 1996;Kukwa 2005aKukwa , b, 2006Kukwa, Szymczyk 2006;Kukwa, Kubiak 2007). Despite its small-sized thallus, this very rare species has distinct, characteristic morphological and chemical features that help to distinguish it from other similar taxa. Its special ecological requirements also make the species noteworthy. C. lucifuga is associated with the bark of old deciduous trees, especially oaks. It seems to have potential indicator properties that may be used to identify high-biodiversity sites and forest communities of special value for protection purposes (cf. Rose 1992;Arup 1997;Nordén et al. 2007).
Caloplaca lucifuga was first reported in Poland by Lipnicki (1993) from the Bory Tucholskie forest. Its localities were later noted in the Puszcza Borecka forest by Zalewska (2000) and in the Puszcza Białowieska forest by Sparrius (2003). Specimens of C. lucifuga were collected from the Puszcza Białowieska forest by H. Sipman and P. van den Boom as early as in 1988; however, the exact location of the sites is unknown (unpbl. data acc. to Sparrius 2003;Sparrius, pers. comm. 2009). Data on the occurrence of C. lucifuga in north-east Poland are provided in a study by Cieśliński (2003), who cites unpublished materials by J. Nowak from the Puszcza Białowieska forest.
The available scarce data on the distribution of Caloplaca lucifuga in Poland are given in this study and its new localities recorded in the Pojezierze Olsztyńskie lakeland are presented on the map.
Habitat requirements of C. lucifuga identified so far suggest that further localities of the species are likely to occur in Poland. The aim of the study was to present the species and to indicate the most important diagnostic characters that help to find it in field studies and to recognise it in herbarium materials.

MATERIAL AND METHODS
The material was collected in 1995-1997 and 2005-2008. Specimens were identified with standard morphological and anatomical methods as well as using spot colour reaction tests to differentiate secondary metabolites (Purvis et al 1992;Orange et al. 2001). The square number of the modified ATPOL grid (Cieśliński, Fałtynowicz 1993) was given for all localities. The nomenclature of lichens follows Fałtynowicz (2003) and Diederich et al. (2009). The material was deposited in the Herbarium of the Department of Mycology, Warmia and Mazury University in Olsztyn (OLTC-L) and in the Herbarium of the Department of Botany and Nature Protection, Warmia and Mazury University in Olsztyn (OLS-L). Thor, Lichenologist 20 (2): 175 (1988).
Ecology. Caloplaca lucifuga was recorded in old oak-lime-hornbeam and oakhornbeam forests in Poland, at sun-exposed or moderately shaded sites with a relatively high air humidity. The species occurred on the bark of old oaks and hornbeams (usually with a trunk girth of over 300 cm) growing by mid-forest roads, less frequently inside forest communities.
According to literature sources, Caloplaca lucifuga clearly prefers the bark of old deciduous trees in woodland tree stands described in different parts of Europe as "wooded pastures" or "wooded meadows" (Thor 1988). Such ecosystems consist of more or less scattered, aged trees and a mosaic of grazing or, less frequently, mowing meadows (Kirby et al. 1995). Known mostly from Scandinavia and Great Britain, they also occur in, for instance, Estonia. These sites have for a long time functioned as extensive pastures and are characterised by a specific ecological continuity. They are important habitats of many rare lichens everywhere (Thor 1988;Laundon 1992;Lepik, Jüriado 2008). C. lucifuga is an indicator species of such areas (Arup 1997;Coppins, Coppins 2002). C. lucifuga also finds similar conditions in very old parks (Thor 1988;Laundon 1992;Hallingbäck 1995). Futhermore, it occurs in denser forests, although usually on the bark of trees growing on the forest edge, e.g. by forest roads.
Caloplaca lucifuga usually colonises deeply cracked bark of very old oaks (Quercus robur, Q. petraea) with a breast diameter of 1-2 m. It was observed on the bark of Castanea, Fagus, Tilia and Ulmus considerably less frequently (Thor 1988). The species is also known from the bark of Aesculus hippocastanum (Brunialti et al. 2001;Aptroot et al. 2001), Acer pseudoplatanus (Palice et al. 2003), Carpinus betulus (Lipnicki, pers. comm. 2009;Zalewska 2000), Castanea sativa (Poelt 1994;Lopez De Silanez et al. 1999), Fagus sylvatica (Spier et al. 2008), Tilia cordata (Türk, Wunder 1999) and Ulmus glabra (Berger, Türk 1993). C. lucifuga was also recorded on dead wood (Clerc 2004). Thor (1988) stresses the species preference for high air-humidity areas (e.g. near lakes, the seaside). He also notes that the lichen mostly grows in deep bark cracks in well-lit sites while it also occurs outside the cracks on flat, raised surfaces, when the shading is greater. The majority of records of C. lucifuga from oak bark are reported for trees with natural properties of the periderm, not impregnated with dusts (Thor 1988;Thor, Arvidsson 1999;Ek, Johannesson 2006). Data from more diversified habitats (Bratli, Haugan 1997) suggest a slightly broader ecological amplitude of the species. Based on studies conducted in the Östergötland county in south-east Sweden on sun-exposed precipices overgrown by oaks, Ek et al. (1995) report that the breast diameter of 62% of old trees with fissured bark colonised by C. lucifuga ranged from 27 to 92 cm. Therefore, the age of the tree and, to a lesser degree, its trunk diameter seem to be major factors conditioning the occurrence of C. lucifuga (Thor 1988).
It seems that the occurrence range of C. lucifuga in Europe is related to the distribution of deciduous forests of the temperate zone. Localities of the species in Sweden and Norway in the Scandinavian Peninsula are situated only in its southern part belonging to the nemoral zone. The lichen also occurs in the sub-Mediterranean zone in the south of Europe, probably at localities situated mostly in the mountains (cf. López De Silanes et al. 1999;Brunialti et al. 2001).
Outside Europe, C. lucifuga is known only from South America. Two specimens of the lichen were collected by H. Sipman and J. Aguirre in Columbia (Lichen Herbarium Berlin, BGBM -WWW).
Caloplaca lucifuga is usually known from few localities in individual countries. It is locally very frequent only in southern Sweden (Hultengren 1994;Ek et al. 1995), from where Thor and Arvidsson (1999) report ca 200 localities. On the other hand, Ek and Johannesson (2006) report as many as 400 records (58% of all records in Sweden) only from the Östergötland county in south-east Sweden. It is also a fairly frequent lichen in the Vosges in France (Aptroot et al. 2001).
RemaRks. As the number of its localities is small, C. lucifuga is considered to be vulnerable in many countries. It is classified as critically endangered (CR) in Finland (Rassi et al. 2001) and is believed to be endangered (EN) in Austria (Türk, Haffelner 1999), Denmark (Søchting, Alstrup 2002), Switzerland (Scheiddeger et al. 2002) and the Czech Republic (Liška et al. 2008). It is classified as vulnerable (VU) in Great Britain (Woods, Coppins 2003) and Norway (Timdal et al. 2006). It is thought to be near threatened (NT) in Sweden (Gärdenfors 2005) and Estonia (Randlane et al. 2008). The species has not been red-listed in Poland due to very scarce data (Cieśliński et al. 2006). However, as habitats characteristic of C. lucifuga are becoming extinct and the number of its localities is small, the taxon seems to fully deserve to be included in the next edition of the red list.

DISCUSSION
Although it forms diminutive and inconspicuous thalli, Caloplaca lucifuga is a fairly characteristic species. It is distinguished by a pale-grey, very thin endophloedic thallus and delimited soralia, yellow-grey to dirty yellowish-orange-brown reacting with K+ violet-red.
Caloplaca chrysophthalma Degel. bears the greatest resemblance to C. lucifuga. The former differs from Caloplaca lucifuga by having a thicker, epiphloedic thallus, grey to yellow (Thor 1988), yellowish-green, yellow-green or grey (Wetmore 2004), with distinct and delimited, usually bright orange-yellow soralia. It rarely produces immersed, poorly developed thalli with scattered, light yellow soralia (Laundon 1992;Wetmore 2004). Furthermore, C. chrysophthalma produces bright orange apothecia, not always present (Thor 1988;Laundon 1992;Wetmore 2004). Clusters of algal cells, present in C. lucifuga, are absent on cross section (Thor 1988). Both species have slightly different chemical properties. C. chrysophthalma also contains parietin (major) as well as additional substances: emodin (minor) and fragilin (minor), instead of fallacinal. Soralia and apothecia react with K+ violet-red. The distribution of both taxa also differs. C. chrysophthalma is mostly known from North America (Wetmore 2004) and from northern Europe, where it occurs in Great Britain (Laundon 1992), Norway (Ihlen 1997) and Denmark, Estonia and Sweden (Thor, Arvidsson 1999). It has few localities in other European countries as well as in Mongolia (cf. sources cited by Culberson et al. 2008) and China (Wetmore 2004). This species has been not recorded in Poland so far (cf. Fałtynowicz 2003). Moreover, Caloplaca chrysophthlma differs from C. lucifuga by its ecological preferences. It is usually associated with trees having natural eutrophic or enriched, dusted bark. In Europe, it is known from such phorophytes as Acer, Fraxinus, Tilia, Ulmus or less frequently from Quercus growing in roadside alleys or other open sites (Hallingbäck 1995;Thor, Arvidsson 1999). In North America, it is a forest epiphyte often found on, old trees of Populus tremuloides (Wetmore 2004).
TLC analysis is not helpful in species identification when fine thalli, such as the ones used in this study, with a very low content of accessory substances, are examined (cf. Thor 1988). Thallus thickness and colour as well as the colour of soralia remain major characters differentiating C. lucifuga from C. chrysophthalma. Habitat data which should, however, be interpreted with care (cf. Bratli, Haugan 1997), may also be useful. It seems that some characters in the descriptions of the morphology and ecology (Thor 1988;Laundon 1992;Wetmore 2004) of both representatives of the genus Caloplaca slightly overlap. The lack of more extensive data available on the frequency of chemical substances recorded and their influence on the colour of soralia as well as data on the structure of fruitbodies and picnidia, not found in C. lucifuga so far, causes some confusion. More wide-ranging chemo-taxonomic examinations of very large collections belonging to 400 records from Östergötland (Ek, Johannesson 2006) and from North America (405 collections, see Wetmore 2004) could be helpful. An analysis of the genetic similarity of both taxa could also provide interesting results.
Buellia violaceofusca Thor & Muhr, another sorediate species, can be found together with Caloplaca lucifuga on old oak trees growing in forests. The former has a similar, pale grey endophloedic thallus with slightly elevated soralia, often confluent and clearly darker, brown tinged violet. The species is known to be sterile (apothecia and picnidia have not been observed). All spot test reactions on the thallus and soralia of B. violaceofusca are negative (Thor, Muhr 1991).
It is finally worth mentioning that the status of C. lucifuga is not clear since, similarly to many other sterile representatives, the species was placed in the genus Caloplaca mostly based on the presence of antraquinones, parietin and fallacinal. These substances occur together with emodin also in other Teloschistales belonging to chemosyndrome A (Arup, Grube 1999). Based on molecular studies, Søchting and Lutzoni (2003) have recently shown that the morphological form of the thallus and the development type of its lower cortex are not good taxonomic characters differentiating the genera Caloplaca, Xanthoria and Fulgensia. It was proven that, for instance, some species of the genus Caloplaca with crustose thalli should be transferred to the genus Xanthoria.

CONCLUSIONS
Based on the current knowledge on the identification and ecology of C. lucifuga and C. chrysophthalma as well as the distribution rate of characteristic habitats preferred by them, it may be suggested that Caloplaca lucifuga is considerably more widespread in Poland but has been poorly differentiated (cf. Wirth 1997). Detailed observations of old oak tree stands, especially within large forest complexes in NE Poland, should be conducted. It seems possible that C. chrysophthalma could also be found in Poland.