Description: Thallus crustose, episubstratic, greenish to grey-green (turning brownish in the herbarium), consisting of 0.1-0.3 mm wide, crowded granular warts forming an up to 10 cm wide crust. Apothecia biatorine, sessile with constricted base, orange-brown to reddish brown, rarely pale ochre, single or often confluent, 0.3-0.6(-1.5) mm across, with a convex, sometimes tuberculate, epruinose disc, and a paler, very thin and soon excluded proper margin. Proper exciple 50-100 µm wide laterally, of radiating hyphae with more or less cylindrical lumina, colourless or more or less uniformly pale brown; epithecium scarcely differentiated from the hymenium; hymenium colourless or pale brown in upper part, 45-70(-95) µm high; paraphyses coherent, simple or sparingly branched, 0.7-2 µm thick at mid-level, the apical cells up to 4 µm wide; subhymenium 40-70 (-120) μm high; hypothecium 95-300 μm high, colourless or pale orange-brown. 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 1-2-septate), hyaline, ellipsoid, (10-)12-20(-25.5) x 4-6(-7) µm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a mostly boreal-montane, circumpolar species ranging from northern Scandinavia to the Alps, Pyrenees and the Balkan mountains, becoming progressively rarer southwards. It is found on epiphytic bryophytes and bark in humid montane forests; reports from plant debris and acid soil most probably refer to B. subduplex.