Hypogymnia tubulosa (Schaer.) Hav.Thallus foliose to subfruticose, heteromerous, dorsiventral, up to 7 cm wide (usually much less), the lobes subcylindrical, 1-3 mm wide, at first adpressed, then soon ascending, up to 3 mm thick, hollow, mostly convex and smooth, dichotomously branched, grey above, black beneath, the tips bearing capitate soralia with farinose soredia. Lower surface black, wrinkled, erhizinate, attached only in the central or basal parts of thallus, otherwise free. Upper cortex of tightly packed, more or less anticlinally oriented hyphae, the cell walls with <i>Cetraria</i>-type lichenan; medulla soon becoming hollow, lining the cavity inside the lobes, white to dark; lower cortex dark, paraplectenchymatous. Apothecia very rare, shortly stalked, lecanorine, with a red-brown disc and a peristent thalline margin. Epithecium brown; hymenium and hypothecium colourless; paraphyses coherent, simple or sparingly branched in upper part. Asci 8-spored, clavate, <i>Lecanora</i>-type. Ascospores 1-celled, hyaline, subglobose or broadly ellipsoid, 6-8.5 x 4.5-5.5 μm. Photobiont chlorococcoid. Spot tests: upper cortex K+ yellow, C-, KC-, P- or P+ pale yellow; medulla K-, C-, KC+ orange-red, P-, UV- or UV+ pale blue-violet. Chemistry: upper cortex with atranorin and chloroatranorin; medulla with physodic acid (major), 3-hydroxyphysodic acid (major), 2'-O-methylphysodic acid (accessory).