Calicium glaucellum Ach.

     Thallus crustose relatively thin, immersed in its substrate, not smooth and more or less warty or grainy, very pale greyish, dirty whitish, light gray with greenish tones especially if moist. Apothecia usually numerous, consisting of a short, stocky stipe 0.5-1 mm high and 0.1-0.2 mm in diameter, very dark brown, blackish, surmounted by a cup, 0.2- 0.4 mm in diameter with fairly high edges and containing a black mazedium. This cup is typically, on very fresh individuals, girdled and bordered with pale gray bands of pruina. Asci long cylindrical 34-41 x 4-6 µm according to the literature, containing 8 aligned spores. Spores elliptical, single septate and cracked surface with small raised ridges, greyish-brown when ripe, 9-13 x 5-6.5 µm according to literature; 10-15 x 5-7 µm according to our measurements. Photobiont: green algae other than Trentepohlia (Trebouxia). Pycnidia sometimes numerous, black. C-, K- sometimes K+/- yellow, KC-, P-. Uncommon species growing on dead wood or bark of deciduous trees such as conifers in humid forests.

Cf. Calicium abietinum very similar species (sometimes to the point of not being separated or misidentified by some authors) but whose apothecia, less stocky, are not pruinose and whose spores and asci are larger in size.