Evernia prunastri (L.) Ach.Thallus subfoliose to fruticose, attached with a basal holdfast, erect and tufted to subpendent, to 12 cm long (usually less), not rigid; branches flattened, strap-shaped to almost linear, dorsiventral, (1-)2-3(-5) mm wide, green to yellowish green (rarely grey) above, white beneath, the upper surface incompletely and shallowly ridged, the margins with irregular, elongated soralia, the soredia finely to coarsely granular, usually white. Cortex thin (especially the lower one), of anticlinally arranged, small-celled hyphae; medulla white, lax, without compact hyphal strands. Apothecia very rare, lecanorine, marginal, substipitate, up to 1.5 cm across, with a brown disc and a thin thalline margin. Proper exciple colourless; epithecium brownish, hymenium colourless; paraphyses mostly simple, thick, septate, hypothecium colourless. Asci 8-spored, clavate, the K/I+ blue tholus penetrated by a faintly amyloid apical cushion with parallel or diverging flanks, the wall K/I-, surrounded by a K/I+ blue outer layer, <i>Lecanora</i>-type. Ascospores 1-celled, hyaline, broadly ellipsoid, 7-11 x 4-6 µm. Pycnidia very rare, c. 0.3 mm across, laminal and marginal, immersed, roundish, with dark ostioles. Conidia pleurogenous, bacilliform, straight, 6-7 x c. 0.5 µm. Photobiont: chlorococcoid. Spot tests: cortex K+ yellow (rarely K-), C-, KC+ yellow (rarely KC-), P-, UV-; medulla K-, KC-, C-, UV-. Chemistry: evernic and usnic acids (the latter absent in the rare var. <i>herinii</i>), atranorin and chloroatranorin. 
