K. Svensk. Vetensk. Avh. Naturskydd., 11: 72, 1955.
Distribution: S - Si (Grillo & Cristaudo 1995).
Description: Thallus crustose, rimose-areolate, granular-warted, pale grey to beige, often with a yellowish tinge; herbarium specimens mostly covered with terpenoid crystals. Areoles 0.1-0.2(-0.5) mm wide, slightly to strongly convex, ecorticate, usually esorediate, very rarely with poorly delimited sorediate patches, the soredia 25-45 µm in diam. Apothecia lecanorine, rounded or irregular in outline, sessile and constricted at base, 0.45-0.7(-0.9) mm across, with a light orange-brown to pinkish ochre, flat to slightly convex, often coarsely pruinose disc, and a usually persistent, slightly crenulate thalline margin which in herbarium specimens is densely covered in white terpenoid crystals and has a byssoid outer appearance. Thalline exciple 40-155 µm wide laterally, 50-190 µm wide basally, filled with small brownish granules soluble in K, composed of irregularly entangled, short-celled hyphae, ecorticate; proper exciple 10-40 µm wide; epithecium pale brown, sometimes with a green tinge, with coarse granules soluble in K; hymenium colourless to yellowish brown, sometimes with orange-brown stripes, (40-)45-60 µm high; paraphyses simple or slightly branched and anastomosing, 1-1.2(-1.5) µm thick; hypothecium colourless or pale yellow. Asci 8-spored, clavate, very thin-walled, with a K/I+ blue, tall tholus penetrated by a faintly amyloid apical cushion, the wall K/I-, surrounded by a blue outer layer, Lecanora-type. Ascospores 1-celled, hyaline, ellipsoid, (7-)10-13(-16.5) x (3.5-)4-5.7(6.5) µm. Photobiont chlorococcoid. Spot tests: thallus and apothecial margin K-, C+ orange, KC+ orange, P-. Chemistry: usnic acid, thiophanic acid, plus variable amounts of arthothelin, 4,5-dichloronorlichexanthone, and traces of 4-chloronorlichexanthone and norlichexanthone; or usnic acid, zeorin and 1 unidentified xanthone.
Note: a pioneer species found on smooth bark, especially on twigs of coniferous trees in upland areas, more rarely on lignum. The species is included in the Italian red list of epiphytic lichens as “Critically Endangered” (Nascimbene & al. 2013c).