Thallus thin, often immersed, smooth, scurfy or finely rimose-cracked, cream-white, buff, rarely pale green or ochraceous. Isidia and soralia absent. Photobiont Trentepohlia.
Anamorph: conidiomata pycnidia. Conidia of two types, bacilliform and 5-8 × 0.7-1 µm in size and ellipsoidal, 3-5 × ca 1.5 µm in size.
Teleomorph: ascomata apothecia, lirellate, 0.6-1.5 (-2) × 0.3-0.5 mm, 150-220 µm tall, scattered or contiguous, usually sessile and simple, straight or curved, the ends acute. Disc initially a slit, soon becoming widely exposed. Exciple K–, sometimes yellow-green or grey-blue pruinose. Epithecium brown, K–. Hymenium 70-110 µm tall, I+ red. Hamathecium of pseudoparaphyses, septate, branched, often richly anastomosed, apices not or rarely slightly swollen. Asci clavate-cylindrical, fissitunicate, 8-spored. Ascospores (20-) 25-33 (-55) × 5-8 (-10) µm, 5- to 7- (to 8-) septate, usually with an enlarged middle cell, with a thin epispore.
Chemistry: thallus C–, K–, KC–, Pd–, UV– (no lichen products detected by TLC).
Assessed by Woods & Coppins (2012) as of Least Concern, but the species was considered to be Nationally Scarce.
Saxicolous forms of Alyxoria (Opegrapha) varia can appear similar to A. mougeotii, but have an exciple that is K+ brown (visible in section).
Scattered throughout the British Isles but mainly found in S England. BLS map here.
On steep, shaded limestone, mortared walls or calcareous sandstone.