Synonyms: Biatora intumescens (Flörke ex Flot.) Hepp; Lecidea intumescens (Flörke ex Flot.) Nyl.; Lecidella intumescens (Flörke ex Flot.) Arnold; Nesolechia intumescens (Flörke ex Flot.) Sacc. & D. Sacc.; Rimularia insularis (Nyl.) Rambold & Hertel; Toninia intumescens (Flörke ex Flot.) Boistel
Distribution: N - Frl (Tretiach & Hafellner 2000), TAA (Lecid. Exs. 279: Hertel 1992b), Lomb, Piem (Isocrono & al. 2003, 2004), VA (Piervittori & Isocrono 1999, Isocrono & al. 2008, Matteucci & al. 2015c), Emil (Tretiach & al. 2008, Fariselli & al. 2020), Lig (Brunialti & al. 1999). C - Tosc (Tretiach & al. 2008), Laz, Sar (Nöske 2000, Rizzi & al. 2011, Brackel & Berger 2019). S - Pugl, Bas (Puntillo & al. 2012), Cal (Puntillo 1996), Si (Brackel 2008b).
Description: Thallus crustose, episubstratic, areolate, grey-brown to dark brown, olivaceous in shade-forms, dull to usually somewhat shiny, up to 0.3 mm thick, often delimited by a dark prothallus, forming more or less orbicular, up to 3.5 cm wide patches on the thalli of Lecanora rupicola s.lat. Areoles contiguous, more or less rounded, convex to almost bullate, 0.2-0.5(-0.9) mm in diam., smooth, corticate. Cortex brown-pigmented above, 10-30 µm thick, overlain with a 2-10 µm thick epinecral layer; medulla white, I-. Apothecia black, lecideine, orbicular to irregular in outline, at first sunken between the areoles, then sessile, not constricted at base, 0.2-0.4(-0.6) mm across, with a flat to slightly convex, dull, epruinose disc and a thin, black, raised, flexuose, persistent proper margin. Proper exciple black-brown in outer part, colourless to brown within, 20-40 µm thick in upper part, 50-70 µm thick in lower part; epithecium olivaceous to brown, 10-15 µm thick; hymenium colourless, 50-75 µm high, I+ red; paraphyses branched and often anastomosing, c. 2 µm thick in lower part, the apical cells submoniliform, slightly swollen, c. 4 µm wide; hypothecium dark brown to black-brown, 100-230 µm high. Asci 8-spored, clavate, with a K/I+ blue tholus with a funnel-shaped central unstained region, and a small, obconical K/I+ blue dome, 35-55 x 11-15 µm. Ascospores 1-celled, at first hyaline, finally often pale brown, ellipsoid, 8-14.5 x (4-)4.5-6(-7) µm. Pycnidia black, immersed in the thallus. Conidia short-bacilliform, c. 4 x 1 µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C+ pink, KC+ pink (reactions often fleeting), P-, UV-. Chemistry: gyrophoric acid.
Note: a widespread holarctic lichen invading the thalli of Lecanora rupicola s.lat.; contrary to the host, it is absent from disturbed habitats.