Lecidea fuscoatra

Lecidea fuscoatra forms a thin crust that breaks into many small, tile-like patches (an areolate thallus). The surface is shiny and whitish grey to pale yellow-brown or grey-brown, each patch usually up to about 3 mm across and flat to slightly rounded. A black border of fungal tissue (the prothallus) may outline the patches. Just above the pigmented outer skin lies a thin layer of dead, colourless cells (an epinecral layer), and the inner white layer (medulla) does not turn blue with iodine.

The fruiting bodies are small black discs (apothecia) 0.5–2(–3) mm wide that are typically sunk into, or seated between, the patches; they are flat to slightly domed and may be dusted with a grey frost (pruina). The disc keeps a slightly raised, persistent rim (the true exciple) that, under the microscope, is built from chains of rounded cells—brown on the outside, colourless within—and it gives a pink reaction in the C test. The uppermost film on the disc (epithecium) is olive-green to olive-brown and becomes more olivaceous in KOH; the spore-bearing layer (hymenium) is 40–60 μm tall; and the tissue beneath (hypothecium) is dark brown to black and often forms a short, stalk-like base. The supporting threads (paraphyses) are mostly unbranched, 1.5–2 μm thick, with tips to 3(–5) μm that can be tinged olive-brown. The spore sacs (asci) measure 45–55 × 8–15 μm and contain eight spores. …

Lecidea fuscoatra is widespread, reported from Europe, North Africa, North America, and Asia. Within Europe it is more frequent on natural, generally acidic rocks (e.g., granite and sandstone) and is relatively common in boreal regions. It has also been recorded growing on hornfels in the Sudety Mountains of Poland. In Galicia (north-west Spain), L. fuscoatra has been recorded on granite church masonry exposed to marine aerosols, for example at the Church of Santa María das Areas (Fisterra), where it occurs on both vertical walls (apse) and horizontal elements, showing that the species readily colonises worked stone in coastal settings.

Several species of lichenicolous (lichen-dwelling) fungi have been recorded growing on Lecidea fuscoatra. These include Endococcus rugulosus, Opegrapha maligna, Polycoccum kerneri, Llimoniella fuscoatrae, Roselliniella lecideae, and Sagediopsis barbara.