K. Svenska Vetensk.-Akad. Handl., 17, 6: 44, 1880. Basionym: Arthonia rhododendri Arnold & Rehm - Flora, 15: 152, 1872.
Distribution: N - TAA (Nascimbene & al. 2007b), Lomb, Piem (Isocrono & al. 2004). C - Sar (Nöske 2000, Brackel 2016).
Description: Thallus crustose, endosubstratic or thinly episubstratic, continuous to patchy, white, yellowish white or grey-white, without a distinct prothallus, doubtfully lichenized. Apothecia lirelliform, black, 0.2-0.8(-1.5) x 0.06-0.2(-0.3) mm, straight or curved, simple or sparingly branched, rarely round, semi-immersed to sessile, with an initially concave and slit-like, later exposed disc, and a shiny, persistent proper margin. Proper exciple prosoplectenchymatous, black, carbonized, 20-25 µm wide laterally, not extending below the hymenium; epithecium brown-black to green-black, without crystals, K-; hymenium colourless, 30-55 µm high, I+ reddish orange; paraphyses thread-like, mostly simple, strongly coherent, the apical cells 3-4 µm wide; hypothecium poorly developed, colourless to yellowish brown. Asci 6-8-spored, elongate-clavate, the apical thickening with an internal beak, K/I-. Ascospores 1-septate, with unequal cells, slightly constricted at septum, at first hyaline, then brownish, sole-shaped, 10-16 x (4-)5-6(-7) µm. Photobiont trentepohlioid or perhaps absent. Spot tests: thallus K-, C-, KC-, P-. Chemistry: without lichen substances.
Note: a rarely collected and rather poorly known species found on twigs of shrubs, with optimum in the subalpine belt the Alps, but also reported from the mountains of Sardegna.