Synonyms: Buellia ryssolea (Leight.) A.L. Sm.; Buellia sejuncta J. Steiner; Buellia subdisciformis var. scutariensis J. Steiner?; Lecidea ryssolea Leight.
Distribution: N - Lig. C - Tosc, Sar (Monte 1993, Scheidegger 1993, Nöske 2000, Rizzi & al. 2011, Neuwirth 2018). S - Si (Scheidegger 1993).
Description: Thallus crustose, episubstratic, rimose to bullate-areolate, up to 1 mm thick, white to pale grey-brown, often delimited by a black prothallus, forming large, often more than 5 cm wide patches, the areoles 0.2-1.3 mm wide, flat to strongly convex. Medulla white, I-. Apothecia lecideine, black, rarely faintly white-pruinose when young, (0.2-)0.4-1(-1.8) mm across, sessile, with a flat to slightly convex disc, and a rather thick, raised, usually persistent proper margin. Proper exciple thick, leptocline-type, homogeneously dark brown, with an additional orange pigment reacting K+ reddish (solution), the inner part of long-celled, interwoven hyphae, the outer part of long-celled, parallel, strongly agglutinated and thick-walled hyphae; epithecium brown, N-; hymenium colourless or pale yellow in upper and lower parts, not inspersed with oil droplets; paraphyses simple to sparingly branched, the apical cells swollen, with a dark cap; hypothecium dark red-brown. Asci 8-spored, clavate to cylindrical-clavate, the apical dome K/I+ dark blue with a pale, conical-pointed apical cushion (axial mass), the wall I-, but the thin outer gel I+ blue, Bacidia-type. Ascospores 1-septate, brown, oblong to ellipsoid, with obtuse ends, (9-)11-16(-20) x (5-)6-8(-10) µm, Physconia-type, with a microrugulate ornamentation. Pycnidia black, semi-immersed in the thallus. Conidia bacilliform, 6-14.5 x 0.8-1.5 µm. Photobiont chlorococcoid. Spot tests: K+ yellow turning red, C-, KC-, P+ yellow-orange, UV-. Chemistry: atranorin, norstictic, and secalonic acids, plus traces of other substances of the stictic acid complex.
Note: a mild-temperate to humid subtropical species found on siliceous rocks at low elevations, chiefly Mediterranean-Atlantic in Europe and Tyrrhenian in Italy. The records from Lombardy by Valcuvia & al. (2003) and Delucchi & Valcuvia (2004) are dubious.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly sexual
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)