Distribution: N - Ven (Lazzarin 2000b), Lig. C - Tosc, Sar (B-189700). S - Cal (CLU 12860).
Description: Thallus crustose, episubstratic, rather thin, rimose or areolate, white, often forming patches of more than 5 cm in diam., sometimes delimited from conspecific thalli by a black prothallus; medulla amyloid, 1+ violet. Apothecia lecideine, black, 0.4-0.8 mm across, sessile and constricted at base, with a flat to convex disc and a thick, prominent, persistent, often sinuous proper margin. Proper exciple c. 100 µm wide, 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; hymenium colourless, without oil droplets, c. 80 µm high; hypothecium dark reddish brown. Asci 8-spored, Bacidia-type. Ascospores 1-septate, brown, oblong, constricted at septum, 12-14 x 6-7.5 µm, Physconia-type, with a microrugulate ornamentation. Pycnidia flask-shaped, black, immersed in thallus. Conidia bacilliform, 4.5-7.5 µm long. Photobiont chlorococcoid. Spot tests: thallus K+ yellow, C+ red, KC+ red, P- or P+ very faintly yellow. Chemistry: atranorin, gyrophoric and lecanoric (trace) acids.
Note: on steeply inclined surfaces of hard siliceous rocks, mostly not far from the coast.