Porpidia flavocruenta

Porpidia flavocruenta forms a thin to moderately thick, yellow–orange crust on rock surfaces, usually cracked into small areoles with an uneven, slightly warted surface from which the fruiting bodies arise; a narrow black border (prothallus) is often visible where it meets other lichens. The fruiting bodies (apothecia) are relatively large for the genus (typically about 1–1.5 mm across), black and round with a persistent raised rim, and often carry a dusting (pruina) that makes the disc appear grey or orange; they sit on the surface of the thallus and are slightly pinched in at the base. Field workers in the Harz have emphasised that the combination of a bright orange thallus and usually strongly pruinose apothecia makes the species relatively easy to recognise on exposed rock faces. In section the hymenium is clear and stains blue with iodine, and it overlies a dark brown tissue (hypothecium) and a strongly pigmented apothecial rim (excipulum) made of thick-walled cells whose inner part is orange-brown and whose outer edge is blue-black; when this tissue is treated with potassium hydroxide solution (the K test) it releases a vivid crimson solution, a distinctive pigment reaction that helps separate the species from similar orange Porpidia taxa. …

Porpidia flavocruenta is a saxicolous (rock-dwelling) lichen that grows on siliceous, usually acidic rocks in cool, moist upland environments. In the British Isles it has been recorded from numerous sites in the Scottish Highlands and in upland Wales, typically on boulders and crags in shaded rock overhangs or other persistently damp microhabitats. Beyond Britain and Ireland it has been found in northern Sweden around Abisko and in the Austrian Alps, as well as in Norway and Iceland, usually in similar montane settings, and it is also known from North America. Fryday suggested that many past records filed under the closely similar orange species P. flavicunda probably include misidentified P. flavocruenta, so the species is likely to be more widespread than current confirmed records suggest. It was reported for the first time from Poland in 2010, from basalt outcrops in the Mały Śnieżny Kocioł cirque in the Karkonosze Mountains of the Sudetes, where it is known from a single montane locality. …