Distribution: N - Ven (Nascimbene & al. 2013b), TAA (Nascimbene & al. 2007b, Trindade & al. 2021), Lomb, Piem (Morisi & Sereno 1995), VA (Matteucci & al. 2008c), Emil (Fariselli & al. 2020), Lig (Arup & Sandler 2011). C - Tosc, Laz, Abr, Sar (Monte 1993, Cossu & al. 2015). S - Camp, Bas, Cal, Si (Campisi & al. 2020).
Description: Thallus foliose, heteromerous, dorsiventral, rather loosely adpressed, forming 2-4(-15) cm wide rosettes. Lobes (1-)2-3(-4) mm wide, dark brown to blackish in sun-forms, smooth to wrinkled, often shiny especially at lobe tips, with more or less cylindrical, often branched and coralloid, up to 1.5 mm tall, 0.07-0.12 mm thick, often branched isidia which easily break off, leaving white scars, the marginal parts usually isidiate. Lower surface dark brown to black, paler-toward the edges, with mostly simple, up to 1 mm long rhizines. Upper cortex paraplectenchymatous, with a pored epicortex, the cell walls containing isolichenan; medulla white, sometimes patchily orange-brown in lower part; lower cortex paraplectenchymatous. Apothecia rather rare, lecanorine, sessile, to 6 mm across, with a concave to flat disc, and a papillate-isidiate thalline margin. Epithecium brown; hymenium and hypothecium colourless. Asci 8-spored, clavate, Lecanora-type. Ascospores 1-celled, hyaline, ellipsoid to broadly ellipsoid, 10-14 x 5-9(-10) μm. Pycnidia rare, dark, immersed. Conidia bacilliform, slightly swollen at ends, 6-7.5 x 1 μm. Photobiont chlorococcoid. Spot tests: upper cortex K-, C-, KC-, P-, N-; medulla K- or rarely patchily K+ red in the orange-brown parts, C+ red, KC+ red, P-. Chemistry: medulla with lecanoric acid, sometimes with a K+ red pigment in patches.
Note: a mainly silicicolous species (see Arup & Sandler Berlin 2011); the greatest majority of the post-1993 records of M. fuliginosa from Italy refer to M. glabratula.