Myriospora myochroa (M. Westb.) K. Knudsen & Arcadia
in Linda in Arcadia & Knudsen, Opuscula Philolich., 11: 22, 2012. Basionym: Silobia myochroa M. Westb. - Lichenologist, 43: 14, 2010.
Synonyms: Acarospora lesdainii auct. non Harm.; Acarospora smaragdula subsp. lesdainii auct. non (Harm.) Clauzade & Cl. Roux
Distribution: N - Frl (Tretiach & Hafellner 2000, Knudsen & al. 2017), Piem, Lig. S - Cal (Puntillo 1996), Si.
Description: Thallus crustose, episubstratic, grey-brown to dark brown-black, rarely grey-white, areolate-subsquamulose. Areoles scattered to contiguous (0.6-)1-2.5(-5) mm wide, flat to strongly convex, epruinose; lower surface pale, ecorticate. Epinecral layer 30(-45) μm thick; cortex 30-60 μm thick, with crystals of norstictic acid visible in polarized light/phase contrast; algal layer interrupted by thick anticlinal bundles of medullary hyphae. Apothecia lecanorine, immersed, 1-4(-14) per areole, 0.2-0.7 mm across, with a concave to flat, brown to dark brown, uneven disc, and a thin thalline margin. Epithecium brown; hymenium colourless, 120–230 μm tall; paraphyses 1-1.5 μm thick, the apical cells hardly swollen, to 2 μm wide; hypothecium colourless to yellowish grey, inspersed with oil droplets, 70-90 μm high. Asci 100-200-spored, clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, narrowly ellipsoid, 3-5 x 1-1.5 μm. Pycnidia rare, immersed. Conidia ellipsoid c. 2 x 1 μm. Photobiont chlorococcoid. Spot tests: thallus K+ or K+ dirty yellow (mostly in fresh material), C-, KC- P-, UV-. Chemistry: norstictic acid in very small amounts, detectable only by TLC, and not in all samples.
Note: in underhangs of metal-rich siliceous rocks in upland areas; probably more widespread in the Alps and occurring also in the Mediterranean mountains. This taxon was erroneously called M. hassei by Nimis (2016).