''Placocarpus schaereri'' is a species of

saxicolous This glossary of mycology is a list of definitions of terms and concepts relevant to mycology, the study of fungi. Terms in common with other fields, if repeated here, generally focus on their mycology-specific meaning. Related terms can be found ...

(rock-dwelling),

areolate Lichens are symbiotic organisms made up of multiple species: a fungus, one or more photobionts (an alga and/or a cyanobacteria) and sometimes a yeast. They are regularly grouped by their external appearance – a characteristic known as their gro ...

, and

crustose lichen Crustose lichens are lichens that form a crust which strongly adheres to the Substrate (biology), substrate (soil, rock, tree bark, etc.), making separation from the substrate impossible without destruction. The basic structure of crustose lichen ...

in the family

Verrucariaceae Verrucariaceae is a family of lichens and a few non-lichenised fungi in the order Verrucariales. The lichens have a wide variety of thallus forms, from crustose (crust-like) to foliose (bushy) and squamulose (scaly). Most of them grow on lan ...

. Found in Europe and West Asia, it is the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

of genus '' Placocarpus''. Juvenile forms of ''Placocarpus schaereri'' are often

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

on the lichen '' Protoparmeliopsis muralis''.

Taxonomy

The lichen was first described scientifically in 1831 by

Elias Magnus Fries Elias Magnus Fries (15 August 1794 – 8 February 1878) was a Swedish mycologist and botanist. He is sometimes called the Mycology, "Linnaeus of Mycology". In his works he described and assigned botanical names to hundreds of fungus and li ...

, who called it ''Parmelia schaereri''. The

species epithet Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In Taxonomy (biology), taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany) ...

honours Swiss pastor and lichenologist

Ludwig Schaerer Ludwig Emanuel Schaerer (11 June 1785 – 3 February 1853) was a Swiss pastor and lichenologist. Interested in natural history from a young age, Schaerer trained as a teacher and studied theology in Bern. During his career as a teacher, orpha ...

. Othmar Breuss transferred it to the newly reinstated genus '' Placocarpus'' in 1985. This species has been known by several

synonyms A synonym is a word, morpheme, or phrase that means precisely or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are a ...

throughout its

taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...

history, including ''Placocarpus saxorum'', ''Endocarpon saxorum'', ''Endocarpon miniatum'' var. ''monstrosum'', ''Placidium monstrosum'', ''Verrucaria monstrosa'', ''Dermatocarpon monstrosum'', ''Verrucaria schaereri'', and ''Catapyrenium schaereri''. The combination of unique characteristics—including its growth form, somewhat umbilicate areolae, thick euplectenchymatous medulla with crystals, and distinctive spores—provided sufficient taxonomic evidence to separate ''Placocarpus'' as a genus distinct from ''

Verrucaria ''Verrucaria'' is a genus of lichenized (lichen-forming) fungi in the family Verrucariaceae. Taxonomy The genus was circumscribed by German botanist Heinrich Adolph Schrader in 1794, with '' Verrucaria rupestris'' assigned as the type species. ...

'', with ''P. schaereri'' serving as the

for this reinstated genus.

Description

While superficially resembling species in the genus ''Verrucaria'', ''P. schaereri'' is distinguished by its larger size and several taxonomically significant characteristics in its anatomy and reproductive structures. The

thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...

(main body of the lichen) is thick, reaching up to 2.5 mm due to an extensively developed

medulla Medulla (Latin for "marrow") or medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ...

(inner layer). The central portions of the thallus display a cracked, pattern, while the outer edges show a more or less distinctly (outward-spreading) form. The areolae (small, island-like segments of the thallus) are attached to the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

by short stalks composed of densely packed, perpendicularly arranged fungal filaments (

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one o ...

e) that extend from the medulla. The outer have a significant portion of their undersides free from the substrate, with a blackening (cellular) lower cortex, giving well-developed specimens an almost lobate appearance. The thick medulla consists of interwoven hyphae densely filled with minute colourless crystals or (comparable to the medulla in the Lecanoralean genus ''

Squamarina ''Squamarina'' is a genus of lichens in the family Stereocaulaceae. They form patches of radiating or overlapping scales (), with a well-developed upper and no lower cortex. They grow on calcareous soil and rocks. '' Squamarina lentigera'' c ...

'') and slowly turns blue when treated with iodine. The spores typically measure 20–28 by 8–10

μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...

and are (surrounded by a gelatinous sheath), with this gelatinous layer being most prominent in premature spores, reaching approximately 2.5 μm in thickness. As this feature appears only during a relatively brief period of spore development, it had been overlooked by earlier researchers. Beyond its anatomy and spores, ''P. schaereri'' is further distinguished from the genus '' Catapyrenium'' by its areolate appearance, which develops from the cracking of what was initially a continuous crust. In contrast, the thallus in ''Catapyrenium'' consists of (scale-like structures) that develop individually from the (the initial growth of the fungal component).

Habitat and distribution

''Placocarpus schaereri'' is typically found in dry, open habitats on

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

substrates, particularly favouring

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

and dolomite rocks. In Austria, the lichen has been recorded from sunny, south-exposed rock surfaces, often in hot and dry (xerothermic) conditions. The species tends to occur in areas characterised by sparse vegetation, frequently co-occurring with other lichens adapted to similar arid conditions. Austrian populations of ''Placocarpus schaereri'' are primarily concentrated in the southern

Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...

. In Slovenia, it has been reported from dry, vertical to inclined rock faces near

Črni Kal Črni Kal (; ) is a village in southwestern Slovenia in the City Municipality of Koper. It is best known today for the Črni Kal Viaduct, the longest and the highest viaduct in Slovenia. Name The name ''Črni Kal'' literally means 'black pond', b ...

, where it grows alongside lichens such as '' Caloplaca inconnexa'', '' Rinodina lecanorina'', and '' Candelariella medians''. In Ukraine, it was reported from the

Medobory Nature Reserve The Medobory Nature Reserve () is a protected nature reserve of Ukraine located in the Podolian Upland in the western part of the country. It protects a representative portion of the "Tovtry" region, known for rocky limestone ridges. The reserve ...

. ''Placocarpus schaereri'' is also known to occur in Turkey, and Iraq.

References

{{Taxonbar , from1=Q10632548 , from2=Q59491857 , from3=Q108474256 , from4=Q49447485 Verrucariales Lichen species Lichens described in 1831 Lichens of Europe Lichenicolous lichens Taxa named by Elias Magnus Fries Lichens of Western Asia