Syn. Meth. Lich.: 14, 1814. Basionym: Lecidea lapicida var. lithophila Ach. - K. Vetensk.-Akad. Nya Handl., 29: 233, 1808.
Synonyms: Lecidea farinosa H. Magn.; Lecidea heteromorpha H. Magn.; Lecidea lithophiliza Nyl.; Lecidea ochracea Fée; Lecidea pruinosa auct.; Lecidea silacea var. lecanactis A. Massal.; Lecidella lithophila (Ach.) Arnold; Lecidella pruinosa Körb.
Distribution: N - Ven (Lazzarin 2000b), TAA (Lecid. Exs. 268: Hertel 1992b, Hertel & Schuhwerk 2010), Lomb, Piem (Isocrono & al. 2004), VA (Borlandelli & al. 1996, Piervittori & Isocrono 1997, 1999), Emil (Fariselli & al. 2020), Lig. C - Tosc, Sar (Neuwirth 2018). S - Camp.
Description: Thallus crustose, usually thinly episubstratic, continuous to rimose-areolate, grey-white to ochraceous, sometimes patchily rust-red (on iron-rich substrata), the areoles flat to slightly convex, forming large patches and sometimes mosaics, the individual thalli separated by black lines; sometimes however the thallus is poorly developed and hardly evident. Medulla white, I-. Apothecia lecideine, black to brown-black but turning dark red-brown when wet (wait for a few minutes), appressed-adnate to finally sessile, not constricted at base, 0.3-1.5(-2) mm across, round to irregular in outline by mutual compression, with an often cracked to deeply split, flat to slightly convex, blue-pruinose (in young apothecia) to epruinose disc, and a flexuose, raised, persistent proper margin. Proper exciple dark brown to greenish brown in outer part, colourless or pale brown within, of intricate-radiating hyphae, the marginal cells thin-walled, 1-3 µm thick, the medullary part filled with minute crystals; epithecium brown to rarely olive-brown, K-; hymenium colourless, 40-75 µm high, I+ blue; paraphyses coherent, simple or rarely branched, 1.5-2 µm thick at mid-level, the apical cells 3-4 µm wide; hypothecium colourless, I+ intensively blue. Asci 8-spored, narrowly clavate, thick-walled, with a K/I+ pale blue tholus and a strongly amyloid, thin apical cushion, surrounded by a I+ blue outer layer, Lecidea-type. Ascospores 1-celled, hyaline, narrowly ellipsoid, sometimes pseudodiblastic (containing 2 large oil droplets), 9-15 x (4-)4.5-7 µm. Pycnidia dark, immersed. Conidia bacilliform, 12-18 µm long. Photobiont chlorococcoid. Spot tests: thallus and medulla K-, C-, KC-, P-, UV-. Chemistry: planaic acid (major), 4-0-demethylp1anaic acid (usually traces).
Note: an ecologically wide-ranging, pioneer species found on vertical to slightly inclined surfaces of acid siliceous rocks close to the ground, also on iron-rich substrata, with optimum above the montane belt. The world distribution was mapped by Hertel (2006).