Lecanora expallens Ach.
Thallus crustose 5-10 cm across, granular, more or less cracked, yellowish-gray, yellowish-green, greyish-green in dry weather and in well-lit areas but "mint" green, bluish-green in areas in the shade, covered with yellowish farinose soralia in dry weather giving green soredia in the shade and in humid weather which gives an areolate appearance to the thallus, grayish prothallus sometimes hardly visible. Species most often sterile, if not small and more or less aborted apothecia, sessile, 0.4-1 mm in diameter, disc convex, pinkish, pinkish yellow, pale pinkish brown, soredate margin quickly excluded. Spores simple, elliptical, 10-16 x 4-8 µm. Photobiont: Trebouxia. C + yellow-orange to dark orange (sometimes faint), K + yellow (sometimes pale), KC +/- orange, P-. Fairly common species occurring on tree bark in non-humid and rather dry areas (edge â€‹â€‹or alignment trees), rare on bare wood (but see Lecanora expallens forme lignicole) and on rocks. See Pyrrhospora quernea more yellowish-ocraceous with a blackish prothallus and sometimes fertile with dark red-brown apothecia (KC + orange, C + bright orange) and Lecanora barkmaniana with a grayish thallus (C-, K + yellow, P + yellow or P-).
N.B. Lecanora compallens is very similar and differs only by its chemistry: C-, K-, to the point that some authors group the two species together!