Distribution: N - TAA, Lomb, Piem (Isocrono & al. 2004), Lig. C - Tosc, Sar. S - Camp, Pugl (Jatta 1909-1911), Cal (Puntillo 1996), Si (Grillo 1998, Grillo & Caniglia 2004).
Description: Thallus crustose, thin and poorly developed, smooth or granular, grey to grey-brown. Apothecia lirelliform, black, solitary or in small clusters, round, ellipsoid or more commonly sinuous-elongate, often branched, (0.2-)0.5-1.5(-2) x 0.15-0.25 mm, with a slit-like, epruinose disc, and a thick, persistent proper margin. Proper exciple black, carbonized, continuous below the hypothecium, 13-18 μm thick laterally and 40-60 μm at the base, K+ greenish; epithecium brownish; hymenium colourless, 60-70 μm high, I+ reddish; paraphysoids branched and anastomosing, c. 1 μm thick, the apical cells hardly swollen; subhymenium grey-brown, I+ reddish; hypothecium black. Asci 8-spored, cylindrical-clavate, the inner layer of the endoascus amyloid throughout, the apical ring hardly visible (vulgata-type). Ascospores 5-7-septate, hyaline, fusiform, straight or slightly curved, 20-35 x 2.5-5 μm, with a 1-1.5 μm thick, gelatinous perispore. Pycnidia black, very small, sunken in thallus. Conidia straight, bacilliform and 3-5 x c. 1 μm, or filiform, curved, and 10-14 μm x c. 0.5 μm. Photobiont trentepohlioid. Spot tests: K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: on vertical to underhanging surfaces of hard siliceous rocks in deep gorges or in mature forests. Closely related to O. vulgata.
Growth form: Crustose
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)