Calicium abietinum Pers.

  Thallus crustose more or less immersed in its substrate, irregular surface, whitish, pale grayish with greenish tones if moist. Apothecia composed of an inverted bell "head" 0.2-0.3 mm in diameter, brown-black, blackish, black arranged on a stipe 0.6-1 mm high, brown-black a little olive, the whole being devoid of pruina. Asci long cylindrical containing 8 spores arranged in a line, 44-52 x 4-5 µm according to the literature; 45-50 x 4-5 µm according to our measurements. Spores elliptical, grey, 1 septate, warty and slightly cracked, 11.5-15 x 5-7 µm according to literature; 12-15 (16) x 5-7 µm according to our measurements. Photobiont: Trebouxia. C-, K-, KC-, P-, I-. Rare species (or going unnoticed!) occuring mainly on the bare wood (and rarely on the bark) of conifers and less often deciduous trees.

N.B. Very close species (and often confused!) with Calicium glaucellum which can be distinguished (sometimes with difficulty!) by its stockier, white pruinose apothecia and by the smaller size of its spores and asci.