Blastenia ferruginea (Huds.) A. Massal. = 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. Pycnidia appearing as red dots. 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: Blastenia (Caloplaca) crenularia !

_ In the Mediterranean region see: Blastenia xerothermica a very similar species whose pycnidia are black.