Roccellographa circumscripta (Taylor) Ertz & Tehler morpho sorediata

    Thallus crustose, more or less round-shaped, to 5 cm diam., 0.2-0.3 mm thick, smooth to minutely verrucose, whitish to pale grey tinged blue in dark sections, light yellow in more lit sections, surrounded by a wide black prothallus, covered with soralia irregular in shape, 0.5-2 mm, pale blue-grey. C- (sometimes yellow due to Trentepohlia when the thallus surface is eroded, K+ pale yellow, KC -, Pd+ bright yellow. In shaded overhangs of acid rocks of the xeric supralittoral zone and the aerohaline zone, also in crevices of shaded walls of rocks near the seashore. Very similar to Roccellographa (Peterjamesia) circumscripta which is frequently found together in small colonies but less frequent. Species belonging to the Sclerophytetum circumscriptae forming mosaics in association with  Arthonia endlicheri, Dirina massiliensis f. massiliensis, Llimonaea sorediata, Arthonia atlantica, etc. N.B. In the field, very difficult to  distinguish from Arthonia atlantica (that may grow in the same habitat and with almost similar chemical reactions) without detailed analysis.*