Lecanora cenisia is a species of crustose lichen in the family Lecanoraceae, first described by the Swedish lichenologist Erik Acharius in 1810 and named after Mont Cenis where it was discovered. The lichen forms a cream-white to pale grey granular thallus with distinctive red-brown to black (fruiting bodies) (apothecia) that feature persistent containing conspicuous crystal clusters. It produces secondary metabolites including atranorin, chloroatranorin, and roccellic acid, which yield characteristic chemical reactions in spot tests. In the United Kingdom, it occurs locally on silica-rich rocks in shaded or sheltered crevices throughout Britain's upland areas and offshore islands, and serves as a host for the lichenicolous fungus Carbonea supersparsa.
Lecanora cenisia was first scientifically described by the Swedish lichenologist Erik Acharius in 1810. In his original Latin description, Acharius noted the species inhabits rocks on Mont Cenis ('), which is alluded to in its specific epithet cenisia. At the end of the protologue, Acharius acknowledged it as a beautiful species () with a distinctive appearance compared to related taxa. He credited Cl. Molinero with discovering it, though he expressed uncertainty about where and under what name it had been previously published.
Lecanora cenisia forms a more or less continuous, granular crustose lichen thallus (the main body) or, alternatively, discrete warted (small, cushionâÂÂlike sections) that may occur singly or in clusters. The thallus ranges from creamâÂÂwhite to pale or yellowish grey, drying to blueâÂÂgrey or pale grey, with areoles that are broadly flat and edged by smooth to scalloped (crenate) margins. A white or bluish (the fibrous fungal growth margin) may be visible around the thallus, and no soredia (powdery vegetative propagules) are produced.
The apothecium (sexual fruiting body) is 1âÂÂ2.5 mm in diameter, on the thallus and often narrowed at the base so that it appears slightly raised. Each apothecium bears a persistent âÂÂan outer rim of thallusâÂÂderived tissueâÂÂthat is entire to finely scalloped or gently wavy, and contains conspicuous clusters of crystals in its medulla. The varies in colour from redâÂÂbrown to black, yellowish brown, grey or greenâÂÂblack, occasionally with a pale frostâÂÂlike () coating.
Microscopically, the (the layer immediately above the hymenium) is brown to oliveâÂÂbrown with coarse that dissolve and turn green in potassium hydroxide solution (K+) and give a purpleâÂÂred reaction in nitric acid (N+). The hymenium (sporeâÂÂbearing layer) is 60âÂÂ90 micrometres (üm) tall, and the paraphyses (sterile filaments among the asci) are 1.5âÂÂ2 üm across with slightly swollen, oliveâÂÂtinted tips. Each ascus measures about 45âÂÂ50 by 7âÂÂ9 üm and contains broadly ellipsoid ascospores that are typically 9âÂÂ15 by 6âÂÂ8.5 üm.
Chemical spot tests on the thallus are CâÂÂ, K+ (yellow or yellow â red) and Pd+ (yellow or yellow â orangeâÂÂred), while showing no fluorescence under ultraviolet light (UVâÂÂ). These reactions correspond to the presence of secondary metabolites such as atranorin, chloroatranorin, roccellic acid, and occasionally gangaleoidin, with variable traces of norstictic acid.
In the United Kingdom, Lecanora cenisia is a locally occurring species found on coarse, silicaâÂÂrich rocksâÂÂparticularly in shaded or sheltered crevicesâÂÂat both inland and coastal sites. It is recorded from the Channel and Scilly Islands and appears in scattered populations throughout Britain's upland areas.
Lecanora cenisiais a known host of the lichenicolous fungus species Carbonea supersparsa.