Lecidea grisella Flörke

    Thallus crustose, thin notably towards the margin, minutely cracked, lately areolate from the center, matt -not glossy- margin thin and minutely cracked but not areolate, grey-brownish, pale grey, prothallus thin, black. Apothecia abundant, 1-2 mm diam., innate, disc flat becoming slightly convex, black, covered with a whitish pruine, exciple hardly visible, persistent, thin. Ascospores simple, hyaline, ellipsoid, 7-16 x 3-8 µm. Photobiont: Trebouxia. Cortex: C+ red, K-, KC+/- red, Pd-. Rather common on siliceous rocks, notably near the seashore, on walls. Sometimes very difficult to distinguish from Lecidea fuscoatra of which the thallus is more brownish, areolate from the very beginning and with a thick and areolate margin.*