Description: Thallus crustose, endo- to episubstratic, forming regular or irregular patches up to a few cm in diam, continuous to areolate, sometimes delimited by a dark prothallus, sorediate. Areoles (when present) grey to grey-green, sometimes with a brownish tinge, flat to convex, more or less rounded, up to 0.3 mm across. Soralia at first punctiform and discrete, flat to slightly convex, up to 0.2 mm across, later more or less confluent, with green to yellowish green or brownish green, 20-30 μm thick, farinose soredia which sometimes coalesce into up to 60 μm thick consoredia. Apothecia rare, lecideine, pale to dark brown, sessile, up to 0.5 mm across, sessile, with a flat disc and a thin proper margin. Proper exciple brown in outermost and uppermost parts, with a faint green tinge in thin sections, otherwise colourless, up to 40 μm wide, with crystals dissolving in K; epithecium brown, with crystals dissolving in K; hymenium colourless or with pale brown vertical streaks, 90-100 μm high, K/I+ pale blue; paraphyses easily made free in K, simple or sparingly branched, 1.5-2 μm thick at mid-level, the apical cells 3-3.5 μm wide; hypothecium colourless to very pale brown, 30-60 μm high, partly K/1+ blue. Asci (6-)8-spored, cylindrical-clavate, with an intensely I+ blue tholus penetrated by a weakly amyloid, broadly cylindrical axial mass, and a poorly developed ocular chamber, Lecidella-type. Ascospores 1-celled, hyaline, broadly ellipsoid, 15-21 x 7.5-9 μm. Photobiont chlorococcoid. Spot tests: thallus K+ yellow, C+ orange, KC+ orange, P+ yellow. Chemistry: atranorin and thiophanic acid (major), arthothelin, expallens-unknown.
Note: on acid-barked trees (conifers, oaks, etc.), with optimum in the montane belt. Known from the Alps outside the Italian territory, but often overlooked, being mostly sterile; to be looked for in Italy.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)