Distribution: N - VG, Frl (Molaro 2005, Tretiach & Molaro 2007), Ven, TAA (Nascimbene & al. 2007b), Lomb, Piem (Isocrono & al. 2004, Matteucci & al. 2013), Emil (Fariselli & al. 2020), Lig (Giordani & Incerti 2008). C - Tosc (Loppi & Frati 2006), Marc (Nimis & Tretiach 1999, Frati & Brunialti 2006), Umb (Genovesi & al. 2002, Ravera & al. 2006), Laz (Massari & Ravera 2002, Ravera & Genovesi 2008), Abr, Sar (Rizzi & al. 2011). S - Camp (Garofalo & al. 2010), Pugl, Bas (Potenza & al. 2014), Cal (Puntillo 1996), Si (Merlo 2004).
Description: Description: Thallus small-foliose to subsquamulose, homoiomerous, gelatinous when wet, 2-10 mm wide, forming rounded cushions often attached by a central point, which sometimes coalesce, covering surfaces to 5 cm across. Lobes few, 0.5-.1.5 mm wide, flattened, adpressed to erect, usually branched, distinctly swollen, with entire, crenate or lobulate margins. Upper surface dark olive-green to brown or black, dull, epruinose, smooth to (rarely) verrucose, without isidia; lower surface usually paler. Upper and lower cortices absent. Apothecia crowded, often hiding the lobes, sessile, with constricted base on lobe margins or terminal 0.5-1.5(-2) mm across; disc plane to convex, dark reddish brown; thalline margin rather thick, eventually disappearing, entire, smooth. Proper exciple to 20 µm thick, euthyplectenchymatous; hymenium colourless, 60-80 µm tall. Asci 8-spored, clavate, the apex thick, with a I+ blue apical dome and a I+ blue annulus projecting downwardly. Ascospores 1(-3) septate, hyaline, fusiform with acute ends, (10-)15-24(-26) x 3-4.5(-5.5) µm. Pycnidia common, immersed, globose. Conidia bacilliform, slightly swollen at the ends, 3-4 x 1 µm. Photobiont cyanobacterial (Nostoc), in long chains. Spot tests: all negative. Chemistry: without lichen substances.
Note: a mainly temperate species with a fragmented holarctic range, found on nutrient-rich bark, especially of Juglans; formerly more widespread, presently restricted to the vicinity of small settlements in mountain valleys, where it is locally abundant.