Calicium viride Pers.

   Thallus crustose, rather thick, granulose, bright green, greenish, yellow-green turning to green-brownish and fading a little with age. Often sterile and, in that case, hardly recognizable; otherwise with small apothecia, 0.2-0.7 mm diam., black in section, heads occasionally powdered in brown, on apices of stalks 1-2 mm high. Asci clavate, formed singly from ascogenous hyphae with croziers, dissolving at an early age. Ascospores ellipsoid, brown, surface with  irregular cracks, 1-septate, constriction at septum level, brown-blackish, surface cracked to rugose (sometimes but seldom at full maturity, with spirally distributed winged excrescences), 11-14 x 4-5 µm according to literature, (10) 12-15 x 5-7 µm according to our measures. Photobiont : Trebouxia. Thallus: C-, K-, KC-, Pd-, UV+  bright orange. Rather common species (but often understated) on barks of deciduous trees or conifers.

N.B. Some specimens only partly developed may resemble Calicium salicinum, but the latter species has a thinner and more greyish thallus and smaller spores.

Cf. Calicium glaucellum whose thallus is thin and pale greyish or whitish with greenish tones and whose apothecia are surrounded by a pale gray dusting.