Lecanora cenisia
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 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.
Taxonomy
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.Description
Lecanora cenisia forms a more or less continuous, granular crustose lichen thallus or, alternatively, discrete warted that may occur singly or in clusters. The thallus ranges from cream‑white to pale or yellowish grey, drying to blue‑grey or pale grey, with areoles that are broadly flat and edged by smooth to scalloped margins. A white or bluish may be visible around the thallus, and no soredia are produced.The apothecium is 1–2.5 mm in diameter, on the thallus and often narrowed at the base so that it appears slightly raised. Each apothecium bears a persistent —an outer rim of thallus‑derived tissue—that is entire to finely scalloped or gently wavy, and contains conspicuous clusters of crystals in its medulla. The varies in colour from red‑brown to black, yellowish brown, grey or green‑black, occasionally with a pale frost‑like coating.
Microscopically, the is brown to olive‑brown with coarse that dissolve and turn green in potassium hydroxide solution and give a purple‑red reaction in nitric acid. The hymenium is 60–90 micrometres tall, and the paraphyses are 1.5–2 μm across with slightly swollen, olive‑tinted tips. Each ascus measures about 45–50 by 7–9 μm and contains broadly ellipsoid ascospores that are typically 9–15 by 6–8.5 μm.
Chemical spot tests on the thallus are C–, K+ and Pd+, while showing no fluorescence under ultraviolet light. These reactions correspond to the presence of secondary metabolites such as atranorin, chloroatranorin, roccellic acid, and occasionally gangaleoidin, with variable traces of norstictic acid.
Habitat and distribution
In the United Kingdom, Lecanora cenisia is a locally occurring species found on coarse, silica‑rich rocks—particularly in shaded or sheltered crevices—at 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.