K. Svenska Vetensk.-Akad. Handl., ser. 3, 7, 4: 72, 1929.
Distribution: C - Sar. S - Si.
Description: Thallus crustose, episubstratic, consisting of a few, scattered to clustered, yellow to ochre-yellow, rounded to angular, strongly convex (but flattened or concave at top), 0.5-5 mm wide, 0.4-0.8 mm thick areoles developing on the thalli of Acarospora hilaris, rarely appearing autonomous due to the death of the host. Upper cortex 120-140 µm thick; algal layer uneven, interrupted by hyphal bundles; medulla white. Apothecia aspicilioid, 1-2(-4) per areole, at first punctiform, then expanded, round to elliptical in outline, 0.2-2 mm across, with a ochre-yellowish disc and a weakly prominent thalline margin. Epithecium yellowish; hymenium colourless 100-130 µm high, I+ blue turning reddish; paraphyses c. 2 µm thick at base, the apical cells hardly swollen; hypothecium colourless. Asci c. 100-spored, clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, globose, 3-4 µm wide. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-, UV+ orange. Chemistry: rhizocarpic acid.
Note: on steeply inclined, sunny surfaces of hard siliceous rocks, especially quartzite, on the thalli of A. hilaris. The species, reported from Macaronesia to Turkey, in Italy is much less frequent than its host, being restricted to the driest parts of the Mediterranean Region.