Pyrrhospora quernea  (Dicks.) Körb.

    Thallus crustose, rather thick, granulose, more or less cracked, typically yellow fawn when dry and yellow fawn with yellow-greenish tinge when moist, entirely covered with granulose soredia, 0.10-0.15 mm diam., prothallus thin, blackish, usually present. Apothecia rare (potentially sterile), in small clusters scattered on the thallus, 0.5-1.5 mm diam., more or less immersed, markedly convex, sometimes irregular, dark brown-red at first becoming brown-blackish to blackish at the end, margin concolourous soon excluded. Ascospores simple, broadly ellipsoid,  8-12 x 6-7 µm. Photobiont: Trebouxia. Thallus : C+ orange, K-, KC+ orange, Pd- or Pd+ pale yellow, UV +/-  dark orange, K/UV+ mint ice cream green. rather common, on bark of trees, notably on Quercus.

_ If infertile it may be difficult to distinguish from Lecanora expallens that also is C+ orange but K+ yellow, without black prothallus and more yellow-greenish, and from Pertusaria flavida, with isidia but without black prothallus.