Lecanora orosthea (Ach.) Ach.
Thallus crustose, rather thick, continuous, more or less cracked, most often areolate, areoles irregular in size and shape, flat, yellowish, yellow-greenish, sulphur yellow, more or less covered with concolourous soralia, yellow-greenish when dry and pale green when moist, prothallus whitish to greyish tinged blue. Apothecia scarce, more or less immersed, less frequently sessile and then prominent, scattered, 0.3-1.5 mm diam., disc brown-pink, yellow-greenish or dark grey, exciple soon excluded. Ascospores simple, ellipsoid, 9-16 x 4.5-6 µm. Photobiont: Trebouxia. Thallus: C-, K+ yellow > brownish, KC+ yellow > yellow-brownish, Pd-. This species is sometimes abundant on sheltered vertical walls of dry siliceous rocks near the seashore, much less frequently inland. Close to Lecanora sulphurea which is considered as the non sorediate form. Besides the lack of soredia, the latter has a thicker thallus and preferentially grows on horizontal surfaces of rocks and boulders.*