Description: Thallus crustose, grey to greyish yellow, inconspicuous, up to 0.1 mm thick, forming patches to 5 mm wide. Cortex usually poorly developed, consisting of an amorphous layer or indistinctly paraplectenchymatous; medulla poorly developed. Apothecia frequent, zeorine, often crowded in small groups, usually adnate, round to somewhat irregular, 0.1-0.5 mm across, with a flat to slightly convex, dark yellow to yellow-orange disc, a thick proper margin concolorous with or brighter yellow than disc, and a pale grey to yellow, well-evident to finally excluded thalline margin. Proper exciple 15–30 μm wide; epithecium orange, granular-inspersed, K+ red; hymenium colourless, 70-90 μm high; paraphyses simple to sparingly branched in upper part, 2-2.5 μm thick, the uppermost cells 4-5 μm wide; hypothecium colourless. Asci 12-16-spored, clavate to subcylindrical, Teloschistes-type. Ascospores 1-septate. polarilocular, broadly ellipsoid, 8-13 x 4.5-7 μm, the septum 3-5 μm thick. Pycnidia rare. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-; apothecia K+ red. Chemistry: thallus without lichen substances; apothecia with parietin (major), fallacinal, emodin, teloschistin and parietinic acid (minor), corresponding with chemosyndrome A of Søchting (1997).
Note: a temperate species found on base- or nutrient-rich bark (e.g. very common on Sambucus or on Juglans in open habitats), with optimum in the submediterranean belt. See also note on A. cerinelloides.