in Kondratyuk & al., Acta bot. hung. 62, 1-2: 100, 2020.
. Basionym: Lecidea lapidicola Taylor - in Mackay, Fl. Hibern. 2: 124, 1836.
Synonyms: Arthonia microsticta auct. (foliicolous specimens); Arthonia muscigena Th. Fr.; Bryostigma lapidicola (Taylor) S.Y. Kondr. & J.-S. Hur; Bryostigma muscigenum (Th. Fr.) Frisch & G. Thor; Catillaria melanobola f. frullaniae B. de Lesd.
Distribution: N - Emil (Fariselli & al. 2020). C - Tosc (Puntillo & Ottonello 1997), Umb (Ravera & al. 2011). S - Cal (Puntillo & Vezda 1994, Puntillo 1995, 1996, Puntillo & Ottonello 1997, Puntillo & Puntillo 2004).
Description: Thallus crustose, endosubstratic or thinly episubstratic, olive-grey to olive-brown, thin, filmy or minutely granular, usually forming patches <5 mm in diam., sometimes poorly evident. Apothecia arthonioid, black, glossy, 0.1-0.3 mm across, slightly constricted at base, with a strongly and irregularly convex, epruinose disc, without a distinct proper margin. Epithecium pale green-brown or red-brown, K+ greenish; hymenium colourless or pale green, 25-30 μm high; paraphysoids very scanty, 0.5-1 μm thick, brown-capped, especially towards apices distinctly oriented horizontally; hypothecium red-brown, 30-70 μm high, K+ olive-brown. Asci 8-spored, clavate, semi-fissitunicate, the apex broad and rounded, very thick-walled. Ascospores 1-septate, hyaline, ovoid to clavate, 8-12(-14) x 2.5-4(-5) μm, often with a slightly pointed end, thick-walled. Pycnidia rare, with a pale brown, K+ olive wall. Conidia bacilliform, 3-4 x c. 0.5 μm. Photobiont chlorococcoid, the cells 6-14(-17) μm wide. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a species with a strongly reduced thallus containing a chlorococcoid photobiont, and minute hemispherical ascomata, sometimes confused with Arthonia apatetica; it grows on the bark of deciduous trees, but also on epiphytic bryophytes (e.g. Leucodon sciuroides), on leaves in humid forests, and sometimes on siliceous rock; it is widespread, but it was probably often overlooked in Italy. All of the Italian samples are foliicolous, but the species should be looked for also on mosses, especially in the Alps. For other details see Sérusiaux (1996) and Cannon & al. (2020). The species is included in the Italian red list of epiphytic lichens as “Vulnerable” (Nascimbene & al. 2013c).