Description: Thallus crustose, endosubstratic or thinly episubstratic and film-like, whitish to pale grey-green. Apothecia micareoid, from the beginning subglobose, often conluent into tuberculate aggregates, dull black, 0.1-0.2 mm across (the aggregates up to 0.3 mm), without a distinct proper margin. Proper exciple mostly indistinct, sometimes evident in young apothecia as a dark narrow zone; epithecium scarcely differentiated from the hymenium, patchily purplish brown, K+ dull green; hymenium colourless, often with vertical, purplish brown streaks, 25-30 µm high; paraphyses scarce, of 2 types: a) evenly distributed, branched, hyaline, 0.7-1 µm thick, the apical cells up to 2 µm wide; b) scattered or gathered in small fascicles, mostly simple, stout, 2-3 µm thick, dark-pigmented throughout; hypothecium mottled dark purplish brown, 70-100(-160) µm high, K+ dark dull green, N+ purple-red. Asci 8-spored, clavate, the I+ blue tholus with a wide, I+ dark blue tube structure that expands towards the top, without a pale axial body. Ascospores 1-celled, hyaline, ovoid or oblong-ovoid, 6.5-12 x 2.5-4 µm. Pycnidia abundant, black, sessile to usually stalked, 60-300 µm tall (incl. stalk), 40-80 µm across, the stalk and the pycnidial wall dark purplish brown, K+ dark green, N+ purple-red. Conidia ellipsoid to short-cylindrical, often biguttulate, 3.4-4.3 x 1.2-1.6 µm. Photobiont micareoid, the cells 4-7 μm wide. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: thallus without lichen substances.
Note: on wood, mostly in boreal-montane coniferous forests and in deeply shaded situations; widespread in Europe, with a single record from the Western Alps (Switzerland); to be looked for in the Italian Alps.