Description: Thallus crustose, thin, continuous to finely rimose, smooth or roughened, grey to yellowish. Apothecia arthonioid, black, round to weakly angular, 0.2-0.5 mm across, with a flat to slightly convex, dull, epruinose disc. Epithecium brown-black; hymenium colourless to pale yellow, 30-60 µm high, not inspersed with oil droplets, K-, I+ orange-yellow; paraphysoids strongly adglutinated, simple or slightly branched, thin, the apical cells capitate, 3-5 µm wide, with a dark brown cap; hypothecium reddish brown in upper part, brown-black in lower part, 30-70 µm high. Asci 8-spored, broadly clavate, semi-fissitunicate, with a large apical dome and a distinct ocular chamber, Arthonia-type. Ascospores 3(-4)-septate, slightly constricted at septa, with subequal cells, hyaline, spindle-shaped, (11-)13-16(-18) x 3-5 µm. Pycnidia dark, immersed to sessile. Conidia bacilliform, 4-6 x c. 1 µm. Photobiont trentepohlioid. Spot tests: thallus K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a cool-temperate to boreal-montane, probably circumpolar, early coloniser of acid bark, mostly of conifers, found both in humid Abies-Fagus forests and in open Larix stands, certainly more widespread in the subalpine belt of the Alps and extending to Calabria along the Apennines.
Growth form: Crustose
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)