Synonyms: Buellia disciformis var. saxicola H. Olivier; Hafellia leptoclinoides (Nyl.) Scheid. & H. Mayrhofer
Distribution: N - Lig (Nordin & Mattsson 2001). C - Tosc, Sar (Scheidegger 1993, Neuwirth 2018). S - Si (Ottonello & al. 2011).
Description: Thallus crustose, episubstratic, thick, whitish, cream-coloured or pale yellowish grey, continuous to rimose-areolate, the areoles 0.3-3 mm wide, often of widely different width on the same thallus, forming patches to over 5 cm in diam, sometimes delimited by a black prothallus. Cortex filled wih large crystals visible under polarized light; medulla white, I-. Apothecia lecideine, black, round or irregular in outline, (0.3-)0.5-0.8(-1) mm across, adnate to sessile, with a flat to convex, epruinose disc, and a finally excluded, sometimes faintly pruinose proper margin. Proper exciple (30-)40-60 μm wide, dispersa-type, of radially arranged hyphae, the inner part of long-celled, parallel, strongly agglutinated and thick-walled hyphae, the outer part filled with crystals reacting K-, of short-celled, isodiametric hyphae without intercellular spaces; epithecium dark brown, N-; hymenium colourless, densely inspersed with oil droplets, 80-120 μm high; apical cells of paraphyses slightly swollen, 2.5-3.5 μm wide, dark brown. Asci 8-spored, clavate, Bacidia-type. Ascospores 1(-3)-septate, brown, 15-20(-23) x (6.5-)8-9(-11) μm, Callispora-type, the inner wall thickened subapically and especially at septum, sometimes slightly curved, the wall smooth or very minutely warted. Pycnidia black. Conidia bacilliform, 4-6 x c. 1 μm long. Photobiont chlorococcoid. Spot tests: thallus K+ yellow, then sometimes brownish, C-, KC-, P+ pale yellow, UV-. Chemistry: placodiolic acid (major), atranorin (minor), chloratranorin (traces).
Note: a probably humid subtropical to mild-temperate species found on steeply inclined surfaces of coastal siliceous rocks subject to humid, salt-loaden winds, more rarely on bark (Giralt & van den Boom 2011); restricted to Tyrrhenian Italy.