Distribution: N - VG, Lig (Valcuvia & al. 2000). C - Marc (Nimis & Tretiach 1999), Laz (Nimis & Tretiach 2004), Abr (Nimis & Tretiach 1999), Sar.
Description: Thallus crustose, episubstratic, continuous to cracked at the periphery, areolate in central parts, very well delimited (sometimes by a black prothallus), forming orbicular patches on the thalli of Circinaria calcarea; the marginal part of the thallus is often radially cracked, giving it an almost placodioid appearance. Areoles angular, flat, smooth, white to pale grey. Apothecia lecanorine-aspicilioid, 0.2-1 mm across, irregular in outline, from round to elongate or angular, immersed in the areoles, with a black, often grey-pruinose, concave to flat, smooth disc, and a very slightly raised thalline margin. Epithecium greenish brown; hymenium colourless; paraphyses more or less branched and anastomosing; hypothecium colourless, subtended by a continuous algal layer. Asci (6-)8-spored, clavate, the thin outer coat K/I+ blue, the wall and apical dome K/I-, Lecanora-type. Ascospores 1-celled, hyaline, broadly ellipsoid, 8-14 x 5-10 μm, 1-2 seriate in the asci. Pycnidia immersed, black, the wall colourless in sections except around the ostiole. Conidia bacilliform, 4-5 x c. 1 μm. Photobiont chlorococcoid. Spot tests: thallus K+ yellow, then blood-red (needle-like crystals), C-, KC-, P+ yellow, UV-. Chemistry: norstictic acid.
Note: a southern European and Mediterranean-montane, very characteristic but often overlooked lichen described from Egypt; it is found on calcareous rocks, starting the life-cycle on Circinaria calcarea and related species; this is the chemotype with norstictic acid only.