Lichenologist, 2: 139, 1963. Basionym: Pyrenotea vermicellifera Kunze in Reichenbach & Schubert - Lich. Exs.: nr. 60, 1823.
Synonyms: Opegrapha fuscella (Fr.) Almb.; Opegrapha hapaleoides Nyl.; Opegrapha leptospora Werner & M. Choisy; Opegrapha mehdiensis Werner
Distribution: N - VG (Tretiach 2015m), Lomb (Valcuvia & Truzzi 2007, 2007b), Piem (Valcuvia 2002, 2002b), Emil (TSB 7994). C - Laz, Sar (Zedda 2002). S - Pugl (Nimis & Tretiach 1999), Bas (Bartoli & Puntillo 1998), Cal (Puntillo 1995, 1996, Puntillo & Puntillo 2012).
Description: Thallus crustose, thin, forming large patches to 12 cm across, smooth or minutely rimose, pale grey to almost white, the fertile form grey-ochre, the sterile form more whitish. Apothecia rare, lirelliform, confined to restricted areas on the thallus, 0.6-1.2 x 0.1-0.3 mm, most often simple and isolated, rarely furcate or stellate in small clusters, half immersed, with a slit-shaped disc and a black to slightly grey-pruinose exciple. Epithecium brown; hymenium colourless, 50-60 µm tall, non-amyloid. Asci 8-spored, clavate-cylindrical, fissitunicate. Ascospores 4-7-septate, hyaline, markedly elongate with pointed ends, 15-25(-30) x 3-4 µm. Pycnidia often abundant (in sterile forms), 0.15-0.25 mm diam., regularly distributed, immersed at first and appearing as brown punctiform ostioles, later prominent, appearing as white-pruinose, to 0.4 mm tall warts. Conidia straight, bacilliform, hyaline, 3-7 x 1-1.5 µm. Spot tests: K-, C- , KC-, P-, UV-. Chemistry: no lichen substances.
Note: a mild-temperate lichen found on old trees in humid areas, especially near large rivers, on faces seldom wetted by rain.