Thallus crustose, epiphloedal, whitish, yellowish or grayish white, continuous, smooth. Vegetative diaspores absent. Photobiont chlorococcoid alga. Ascomata lecanorine apothecia, sessile, not constricted at base, 0.3-0.6(1.2) mm diam.; disk reddish brown to blackish, epruinose, flat to convex; thalline margin (amphithecium) thin, smooth, not raised. Amphithecial cortex 50-100 µm thick at base; medulla with small crystals. Epihymenium orange to orange-brown, persistent in K, lacking crystals; hymenium hyaline, not inspersed; paraphysal tips slightly thickened to capitate; hypothecium hyaline. Asci 8-spored, clavate, thin-walled, with a tall, K/I+ blue tholus and K/I- wall surrounded by K/I+ blue outer layer; ascospores simple, hyaline, ellipsoid, 9.5-13.0(-14.5) × 5.5-8.0 µm, wall < 1 µm thick.
Chemistry. Thallus UV-, K+ yellow, KC-, C-, PD- or + pale yellow; atronorin (major) and unknown terpenoids.
Substrate and Habitat. Corticolous on smooth-bark trees (e.g., Acer, Fagus).
Distribution. Pantemperate (Europe, east Asia, eastern North America); in North Carolina found in the Blue Ridge ecoregion.
Acharius, E. (1810) Licenographia Universalis. Göttingen. 689 pp (original description as Lecanora subfusca γ [var.] glabrata).
Brodo, I.M. & O. Vitikainen (1984) The typification of Lecanora subfusca (L.) Ach., its varieties, and some of its related taxa published before 1850. Mycotaxon21: 281-298.
Nimis P.L. (2023). ITALIC - The Information System on Italian Lichens. Version 7.0. University of Trieste, Dept. of Biology, (https://dryades.units.it/italic), accessed on 2023-02-04.