Synonyms: Aspicilia calcarea var. farinosa auct.; Aspicilia farinosa auct.; Lecanora farinosa auct.; Pachyospora farinosa auct. non (Flörke) A. Massal.
Distribution: N - Frl (TSB 25297), Ven, TAA, Lomb, Emil (Fariselli & al. 2020), Lig (Giordani & al. 2016). C - Tosc (Benesperi 2000a), Umb (Genovesi & Ravera 2001, Ravera & al. 2006), Laz (Nimis & Tretiach 2004), Abr (Gheza & al. 2021), Mol (Nimis & Tretiach, 1999, 2004, Caporale & al. 2008), Sar. S - Camp (Aprile & al. 2003b, Nimis & Tretiach 2004, Garofalo & al. 2010), Pugl (Nimis & Tretiach 1999), Bas (Nimis & Tretiach 1999, Brackel 2011), Cal (Puntillo 2011), Si (Grillo 1998).
Description: Thallus crustose, episubstratic, 0.1-1.1(-1.3) mm thick, white-farinose, continuous to finely cracked, rarely rimose-areolate in central parts, forming orbicular patches to 5 cm across. Areoles 0.4-3(-6) x 0.3-2.5 mm, angular, slightly concave to flat, rarely papillose, sometimes developing on a dark hypothallus. Cortex colourless, paraplectenchymatous, overlain with an epinecral layer, completely filled by coarse crystals soluble in N but insoluble in K, which obscure its structure; algal layer 50-90 μm thick; medulla white, 0.1-0.35 mm thick, I-, filled with crystals. Apothecia lecanorine-aspicilioid, 0.2-1.4 mm wide, round to slightly irregular, immersed in the thallus, with a concave to flat, black, but usually bluish grey-pruinose disc, and a 0.15-0.25 mm thick, raised thalline margin. Epithecium greenish brown, covered in coarse crystals, N+ emerald green, K-; hymenium colourless, 80-120 μm high, without crystals; I+ blue, then reddish brown; paraphyses sometimes submoniliform in upper part, the uppermost cells 2-3 μm wide; hypothecium colourless, underlain by a thin algal layer. Asci 8-spored, clavate, the thin outer coat K/I+ blue, the wall and apical dome K/I-. Ascospores 1-celled, hyaline, broadly ellipsoid to subglobose, (8.5-)10-13(-14.5) x (6.5-)7-9(-10) μm. Pycnidia immersed, more or less pyriform, with a colourless wall (except near the ostiole which is greenish brown). Conidia bacilliform, straight, (4.5)5–6(-6.5) x 1–1.5 μm μm. Photobiont chlorococcoid. Spot tests: chemotype a) K-, C-, KC-, P-; chemotype b) K+ yellow-orange then sometimes reddish brown, C-, KC-, P+ brick red. Chemistry: different terpenoids; stictic and norstictic acid in chemotype b).
Note: a mainly southern species in Europe, found on hard rocks, especially on dolomite, with optimum in the montane belt. The nomenclature of this species has a complicated history, because Flörke used the epithet "farinosa" for Circinaria calcarea (Hafellner & Türk 2001): some old records from the Alps could refer to that species. Specimens from high altitudes differ in several minute anatomical details and could belong to a different species, provisionally called Lobothallia alpina Cl. Roux & M. Bertrand (see Roux & coll. 2020).