K. Svenska Vetensk.-Akad. Handl., ser. 3, 7, 4: 282, 1929.
Synonyms: Acarospora gallica var. devastata (Eitner) H. Magn.; Acarospora hungarica H. Magn.
Distribution: N - VG (Castello 2002, Martellos & Castello 2004), TAA (Nascimbene & al. 2021), Piem (TSB 34247), Emil (Nimis & al. 1996, Fariselli & al. 2020), Lig (Giordani & al. 2016). C - Tosc, Sar (CLU 4578)..
Description: Thallus crustose, episubstratic, of dispersed or contiguous areoles, pale yellowish brown, epruinose, matt. Areoles 0.2-0.4(-1) mm wide, 0.2-0.5 mm thick, usually flat, angular to round, broadly attached, sometimes reduced to a thin rim around a single apothecium, becoming subsquamulose and lobulate in well-developed specimens; lower surface of well-developed areoles pale brown or white. Cortex (15-)20-35 μm thick, paraplectenchymatous; algal layer continuous; medulla white, up to 100 μm thick. Apothecia 1-10(-12) per areole, 0.1-0.6 mm across, with a usually smooth, brown (reddish when wetted), epruinose disc and an indistict thalline margin. Proper exciple thin, to 10-15 μm wide; epithecium reddish brown; hymenium colourless, 75-100 μm high, I+ red or blue; paraphyses 1.5-2 μm thick, mostly simple, the apical cells slightly expanded, up to c. 3 μm wide; hypothecium colourless. Asci 100-200-spored, clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, narrowly to broadly ellipsoid, (2)4-5(-6.5) x 1.5-2 μm. Pycnidia globose, usually visible as brown-red dots. Conidia hyaline, simple, mostly 2.5 x 1 μm. Photobiont chlorococcoid. Spot tests: cortex and/or medulla K-, C+ red, KC+ red, P-. Chemistry; gyrophoric and lecanoric acids.
Note: a probably holarctic species of base-rich, weakly calciferous siliceous substrata, such as calcareous sandstone, brick, and roofing tiles, usually at relatively low elevations; much overlooked or confused with other species and certainly more widespread in Italy. For further details see Knudsen & Kocourková (2012).