Description: Thallus crustose, episubstratic, at first continuous, then rimose-areolate, pale grey to blue-grey, often delimited by a dark prothallus, the areoles slightly convex, often ascending at the edges and resembling minute squamules, finally turning into grey to brown, globulose or flattened schizidia which may cover the whole thallus. Cortex 20-25 µm thick; medulla white, I-. Apothecia usually scarce, lecanorine-aspicilicioid, 1-2 per areole, round, 0.3-1 mm across, with an initially deeply concave, then flat, epruinose disc, and a thin, often poorly evident thalline margin which is often paler than thallus. Epithecium olive-green or olive-brown, N+ bright green, K+ brown-red; hymenium colourless, 130-170 µm high; paraphyses coherent, branched, 1.5-2.5 µm thick in lower part, the apical cells up to 3.5 µm wide; hypothecium colourless, 40-50 µm high. Asci 4-8-spored, clavate, the thin outer coat K/I+ blue, the wall and apical dome K/I-. Ascospores 1-celled, hyaline, subglobose to broadly ellipsoid, 14-30 x 7-16 µm. Pycnidia black, immersed. Conidia thread-like, curved, up to 25 x c. 1 µm. Photobiont cghlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-. Chemistry: thallus with aspicilin.
Note: this isidiate-sorediate species growing on siliceous rocks near the coast has ben reported from several localities in the Mediterranean Region, but also from North America and East Asia, and is common along the Atlantic coasts of France and those of the North Sea (Roux in litt.).
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)