Calicium salicinum  Pers.

   Thallus very thin, rather undifferentiated from substratum, smooth to minutely granular, whitish, greyish, often stained by underlying substrate. Apothecia: globulous cup shaped, with head 0.3-0.5 mm diam., on top of a brown-black stalk, 0.5-1.2 mm high, shaped as a golf "tee", two-coloured: brown-prunose towards the base and blackish to the top. Asci cylindrical of 35-40 x 4-6 µm according to our measurements. Ascospores brown-olive, 1-septate, like a "ball of wool" with an ornementation finely granulose, spirally arranged, 8-11 x 4-4.5 µm according to literature, 7-11 x 3-5 µm according to our measurements. Photobiont : Trebouxia. Thallus: Chemical tests negative or K+ orange and Pd+ yellow-orange. Unconspicuous species, that must be seeked on dry bark or on naked wood (Quercus), sometimes on barks fallen on the ground. See also Calicium viride with a thick and green granulose thallus.