Description: Thallus inapparent, not lichenized, the hyphae developing inside the apothecial discs of Rhizoplaca-species. Apothecia arthonioid, immersed in those of the host, more or less round, to 2 mm across, with a black, often marginally paler, slightly convex disc, without a distinct proper margin. Exciple poorly developed, not evident; epithecium olive-brown, 15-20 µm high; hymenium colourless, 25-35 µm high, I+ red, K/I+ blue; paraphysoids branched, the apical cells enlarged, to 3 µm wide; hypothecium colourless, c. 20 µm high. Asci 8-spored, broadly clavate to subglobose, semi-fissitunicate, with a large, non-amyloid apical dome, and a distinct ocular chamber, Arthonia-type. Ascospores 1-septate, hyaline, obovate, one cell larger and longer, 10-14 x 4-7 µm, without an epispore. Photobiont absent. Spot tests: K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a holarctic lichenicolous fungus growing in the apothecia of Rhizoplaca chrysoleuca, very much confused with other species in Italy (see note on A. galactinaria). Records from other hosts than Rhizoplaca are not reported here.