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. The species does not belong to Arthonia and should be included in the Chrysothricaceae (Frisch & al. 2014)
Growth form: Crustose
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)