Thallus absent, lichenicolous.
Anamorph: not known.
Teleomorph: ascomata apothecia, developing in the hymenium of the host and blackening the disc, 0.3-1 mm diam., black, level with the host disc or slightly more convex. Epithecium brown to olive-brown, K+ pale green. Hymenium 45-60 μm tall, hyaline, I+ blue. Hypothecium hyaline. Interascal tissue of pseudoparaphyses 1.5-2 (-2.5) μm diam., the apices cemented together by dark pigment. Asci clavate, semi-fissitunicate, with a large apical dome and a distinct ocular chamber, 8-spored. Ascospores 11-17 × 5-6.5 μm, ovoid to cylindric-ellipsoidal, (1-) 2- to 3-septate, hyaline, fairly thick-walled, smooth, without an epispore, gelatinous sheath or appendages.
Chemistry: lichen products not known.
Arthonia apotheciorum also occurs on apothecia of Lecanora species, and is like A. varians but the ascospores are narrower and 1-septate.
Lichenicolous, the ascomata developing in the hymenia of Lecanora rupicola.
Common, more or less throughout the range of its host. BLS map here.