Lichens marins - 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.

N.B. Very variable species depending on exposure to light (there are probably several taxa) with an Enterographa appearance sometimes associated with Ingaderia sorediata, (formerly considered as a variety!) but the two species do not have the same colours together: Roccellographa (Peterjamesia) circumscripta has a general greyish-whitish-yellowish colours and Ingaderia sorediata has a general pale grayish colours, slightly bluish in its soredia.

_ Sometimes associated with Sparria endlicheri, in less sunny places but Cliostomum tenerum, Llimonaea sorediata, Dirina massiliensis f. sorediata can also come nearby in slightly brighter places.

- Reichlingia dendritica (Arthonia atlantica) is a fairly similar species which in the field is K+ yellow and P+ pale yellow or pale red and not yellow-orange and which does not leave an orange stain when scratched.