K. Svenska Vetensk.-Akad. Handl., 17, 6: 58, 1880. Basionym: Sphaeria apotheciorum A. Massal. - Ric. Auton. Lich. Crost., 26, fig. 44, 1852.
Synonyms: Arthonia clemens auct. p.p. non (Tul.) Th. Fr.; Conida apotheciorum (A. Massal.) A. Massal.
Distribution: N - Ven (Lazzarin 2000b, Brackel 2016). S - Pugl (Brackel 2016), Cal (CLU 17859), Cal (Brackel & Puntillo 2023), Si (Nimis & al. 1994 as A. clemens, Brackel 2016).
Description: Thallus inapparent, not lichenized, the hyphae developing inside the apothecia of Myriolecis-species, mainly M. albescens. Apothecia arthonioid, immarginate, 0.1-0.4 mm across, at first appearing as small, black dots on the apothecia of the host, then blackening the whole apothecial surface. Proper exciple poorly developed; epithecium dark brown, K+ olive; hymenium colourless, 40-50 μm high, I+ wide-red then blue; paraphysoids 1.5-2 μm thick at mid level, the apical cells 2-4 μm wide, with dark pigmented caps; hypothecium colourless or 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, hyaline, narrowly ellipsoid to subclavate, 9-15 x 3-5(-6) µm. Photobiont absent. Spot tests: K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a parasite in the apothecia of Myriolecis albescens and related species, certainly more widespread in Italy; often confused with other related species, especially with A. clemens.