Description: Thallus crustose, superficial, continuous, very thin, smooth to fine-grained, greyish-green, sometimes evanescent. Apothecia lecideine, 0.1-0.4 mm across, sessile, round, clearly constricted at base, with a concave to flat, whitish to pinkish yellow disc and a thin, smooth, persistent margin. Proper exciple well-developed, paraplectenchymatous; hymenium colourless, 70-90 μm tall, I+ blue then quickly reddish brown, K/I+ blue; paraphyses unbranched, 1-2 µm thick, the apical cells c. 4 µm wide; hypothecium colourless. Asci 8-spored, narrowly cylindrical, the apex slightly thickened to give an amyloid ring around the pore, Catillaria-type, with uniseriate ascospores. Ascospores 1-septate, hyaline, fusiform to ellipsoid, 9-13 x 2-3(-4) μm. Pycnidia more or less immersed, whitish. Conidia oblong, 6-8 x 1.8-2.8 µm. Photobiont trentepohlioid. Spot tests: all negative. Chemistry: no lichen substances.
Note: a probably holarctic lichen, most common on acid bark, both of conifers and of broad-leaved trees, below the subalpine belt; certainly widespread throughout the country, especially in non-heavily disturbed semi-natural areas with a humid climate.