Description: Thallus crustose, thick, continuous to cracked, pale yellowish-green to greenish grey, sometimes delimited by a pale to dark prothallus, often starting the life-cycle on Tephromela-species. Medulla white, I-. Apothecia lecanorine only when young, soon appearing biatorine, 1-2 mm across, at first immersed, then protruding, with a greenish yellow to greenish brown, finally almost black, grey-pruinose, strongly convex, sometimes uneven disc, and a very thin, soon excluded thalline margin. Epithecium olive-green to dirty brown, K+ green-black, with granular crystals dissolving in K; hymenium colourless, 50-95 µm high; paraphyses sparingly branched, 2-2.5 µm thick at mid-level, the apical cells only slightly thicker; hypothecium colourless. Asci 8-spored, clavate, very thin-walled, with a K/I+ blue, tall tholus penetrated by a faintly amyloid apical cushion, the wall K/I-, surrounded by a blue outer layer, Lecanora-type. Ascospores 1-celled, hyaline, ellipsoid, 9-14(-16) x 4-6 µm. Pycnidia black. Conidia thread-like, often curved, 14-20 x 0.5-1 µm. Photobiont chlorococcoid. Spot tests: K+ yellowish brown, C-, KC+ yellow, P-, UV+ dull orange. Chemistry: usnic acid, and atranorin, gangaleoidin, zeorin, α-collatolic acid in variable amounts.
Note: a widespread and locally common lichen which often starts the life-cycle on Tephromela atra, with a wide altitudinal range; in southern and central Italy it is almost as common on limestone as on siliceous rocks. Kondratyuk & al. (2019) included this species in Glaucomaria, but L.
sulphurea certainly does not belong to that genus.