Lich. Scand. 1: 215 (1872) or (1870).
Basionym: Lichen fuscatus Schrad., Spicil. Flor. German.: 88 (1794).
Type locality: Germany, s.c.
Type locality coordinates: Data lacking.
Barcode: Data lacking.
Thallus: crustose, delimited, up to several cm in diameter, wide-spreading and often forming extensive patches, rarely scattered, light brown, areolate. Areolae light brown, dull to shiny, 0.5-3 mm in diameter, very variable, mostly contiguous, irregular, pale to dark reddish or yellowish brown, often with black margins and undersides. Algal layer 40 - 90 µm thick, continuous. Apothecia solitary or 2-5 per areole, usually numerous, at first punctiform, later concave-flat, usually numerous, at first punctiform, later concave-flat, usually angular or irregular, immersed, never elevated or emergent, without thalline margin. Disc smooth or slightly rough, level with thallus or more or less depressed, o,2 - 1 mm diameter, reddish brown to blackish, usually more or less darker than the thallus. Hymenium 80 - 120 µm tall. Epithecium yellowish brown. Hypothecium 40 - 60 µm tall. Exciple distinct, 10 - 30 µm thick. Paraphyses conglutinate, 1.5 µm wide at base, 2-3 µm wide at the apex. Asci 60-85 x 15-17 µm, 100 - to 200-spored. Ascospores 4-6 x 1-2 µm, narrowly ellipsoidal or more or less cylindrical (Østedahl & Gremmen 1995, Temina et al. 2005).
Photobiont: Chlorococcoid.
Ecology: On nitrate rich silicious stone, not rarely on wooden poles of conifers (e.g. Picea abies).
Chemistry: Thallus K-, C+ red, KC+ red. Hymenium J+ blue or red.
Distribution: Cosmopolitan (Galloway 2007: 7). Subcosmopolitan.
Note: Huneck (1962: 374) was the first to clarify that gyrophoric acid causes the redish reaction with C and KC in Acarospora fuscata.
The authorities of Acarospora fuscata are difficult to cite and have been named in many different versions:
Lichen fuscatus Schrad. wurde konserviert (May, T.W. 2017: Report of the nomenclature committee for fungi: 20. - Taxon 66(2): 483-495.).
Chemical race I: Stictic acid complex with a trace of norstictic acid (TLC) (Østedahl & Gremmen 1995, Temina et al. 2005).
Chemical race II: Gyrophoric acid (Huneck 1962: 396). Gyrophoric acid, lecanoric acid (trace), orsellic acid (trace) (Kümmerling 1991: 96).
Acarospora fuscata (Nyl.) Arnold by Verseghy (1994: 228).
Acarospora fuscata (Nyl.) Arnold by Weber & Wittmann (2000 internet) "First author given as Schrader by Zahlbruckner, but evidently the Schrader Lichen fuscatus was probably a synonym of Protoparemlia badia (Lecanora badia var. fuscata Acharius).
Acarospora fuscata (Nyl.) Th. Fr. by Scholz (2000: 15).
Acarospora fuscata (Schrad.) Th. Fr. by Knudsen (2007: 13). He cites the basionym: "Lecanora fuscata Schrad., Spicil. Fl. Germ.: 83 (1794).
Stand am 28.9.2017: IF: Acarospora fuscata (Nyl.) Th. Fr., Lich. Scand. (Upsaliae) 1(1): 215 (1871).
Stand am 28.9.2017: Mycobank: Acarospora fuscata (Nyl.) Th. Fr., Verhandlungen der Zoologisch-Botanischen Gesellschaft Wien 20: 529 (1871) [MB#375564].