Flora, Regensburg 64, 21: 324, 1881.. Basionym: Arthonia apotheciorum subsp. caerulescens Almq. - K. svenska Vetensk-Akad. Handl., ny följd, 17, 6: 59, 1880.
Distribution: S - Bas (Brackel & Puntillo 2023), Cal (Brackel & Puntillo 2023).
Description: Thallus inapparent, not lichenized, the hyphae developing inside the apothecia of Lecanora varia and related species. Apothecia arthonioid, black, rounded, 0.1-0.4 mm across, appearing as small, black dots on the apothecia of the host, then blackening the whole surface, Epithecium dark blue-green or brown with an olive tinge; hymenium 40-50 μm high, I+ blue; paraphysoids 1.5-2 μm thick at mid level, the apical cells with dark pigmented caps, 2-4 μm wide; hypothecium colourless to very pale brown. 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, slightly constricted at septum, hyaline, 10-12 x 4-6 µm. Photobiont absent. Spot tests: K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a lichenicolous fungus growing in the apothecia of Lecanora varia and related species; known among others from Spain, France, North Macedonia and Montenegro.