Caloplaca ferruginea (Huds.) Th. Fr.

    Thallus crustose, thin, minutely granular or cracked squamulose, dull white, pale grey, pale grey-green, seldom with a blackish hypothallus. Apothecia scattered all over the thallus, 0,5-2 mm diam., disc plane, brown-red, redish, bright red, red-orange, with a markedly unevenly flexuose margin, persitent, paler than disc. Ascospores polarilocular, septum 3-6 µm wide, 12-17 x 7-9 µm. Photobiont : trebouxioide. Thallus : K-, apothecia : K+ purple.  Thermophile trend, on bark of deciduous trees in well lit situations. N.B. Very similar to another species growing on rocks:  Caloplaca crenularia !*