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-, UV+ orange, K/UV+/- ochraceous. 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.