Roccellographa circumscripta (Taylor) Ertz & Tehler

   Thallus more or less circular, 1 to 5 cm in diameter, very often forming mosaics, moderately thick, 0.2-0.25 mm, finely powdery with calcium oxalate crystals, rimose to crackle and forming areoles of 1 -2 mm with jagged edges, pale grayish if very fertile, otherwise white-greyish, dirty white a little yellowish, gray-yellowish but becoming orange or orange-yellow if altered or scraped by the presence of the photobiont which is a Trentepohlia, prothallus most often very clear with slightly lacerated, blackish edges. Apothecia up to 0.1 mm in diameter, buried in the thallus and appearing as small black dots, flat, black disc, powdered with whitish. Spores very elongated, brownish when mature, (4) 5 (7) septate, 17-25 x 5-6 µm. C-, K-, KC+ pale yellowish, P+ yellow-orange. Common species of rocky coasts coming under the overhangs of dry siliceous rocks sheltered from rain and direct light.