Description: Thallus crustose, episubstratic, continuous, rimose or verruculose, greenish grey to pale grey. Apothecia biatorine, rounded or slightly irregular in outline, sessile with a slightly constiricted basis, single and 0.3-0.5 mm across, or coalescing-tuberculate and 0.5-1 mm across, with a beige to pale reddish brown, epruinose, flat to moderately convex disc, and a concolorous or paler, thin, soon excluded proper margin. Proper exciple colourless or yellowish, of radially arranged hyphae, laterally 30-70 µm wide, basally much wider, the outer part often with tiny granules of gyrophoric acid forming a smear between the hyphae; epithecium scarcely differentiated from the hymenium, colourless or pale yellow; hymenium 40-60 µm high, colourless or yellowish, the pigmented parts often arranged in thin longitudinal stripes; paraphyses simple or sparingly branched in upper part, 1-1.5(-2) µm thick at mid-level, the apical cells to 2.5-3 µm wide; hypothecium colourless or pale yellow. Asci 8-spored, clavate, with a K/I+ blue apical dome penetrated by a narrow, K/I- apical cushion surrounded by a narrow, deeply K/I+ blue zone, the wall K/I- but surrounded by an I+ red-brown, K/I+ blue outer layer, the ocular chamber relatively small, Biatora-type. Ascospores 1-celled (rarely 1-septate), hyaline, (8.5-)10-14(-17) x 3-5 µm. with a c. 0.5 mm thick perispore. Pycnidia rare, immersed, the wall colourless. Conidia bacilliform. Photobiont chlorococcoid. Spot tests: thallus K-, C- or faintly C+ pink, KC- or faintly KC+ pink, P- (positive reactions often fleeting and poorly evident); apothecial sections fleeting C+ pink. Chemistry: gyrophoric acid (major), and traces of lecanoric acid.
Note: a mainly boreal-montane, circumpolar species found on basal parts of trees in open montane to subalpine forests, often with Parmeliopsis hyperopta; certainly much more widespread in the Alps.