Description: Thallus squamulose-umbilicate, gelatinous when wet, blackish or grey-pruinose, the squamules 5-20 mm wide, flattened, forming rosettes or cushions, distinctly lobulate with loosely adpressed (in central parts) to ascending (in marginal parts) lobules, the surface with small, globose, isidia-like outgrowths, the tips rounded, with down-turned margins; lower surface attached by a central holdfast. Thallus ecorticate, 110-225 μm thick, the central part occupied by a 50-175 μm thick, loose hyphal strand without photobionts. Apothecia thallinocarp, marginal to submarginal, appearing as round to irregularly shaped, flat to convex, brown swellings best visible in the wet state. Proper exciple absent; epithecium brownish; hymenium colourless, finally separated into partial hymenia by intrusions of wedge-shaped, sterile thalline tissue, covered by a continuous layer of sterile tissue separated only by the pore-like discs of the partial hymenia, I+ blue turning wine-red. Asci 16-32-spored, with a thin, one-layered, non-amyloid wall, an amyloid external apical cap, and passive spore discharge via apical rupturing. Ascospores 1-celled, hyaline, broadly ellipsoid, 5-9 x 3-5 μm. Photobiont cyanobacterial, chroococcoid, with a few cells penetrated by haustoria and surrounded by a brownish gelatinous sheath. Spot test: all negative. Chemistry: without lichen substances.
Note: a critical taxon, purported to be most frequent in humid stands by rivers. The type is from France: "sandstone boulders along the Arve near Mornex". The only Italian record needs confirmation. An earlier record from Emilia (see Nimis 1993: 422) proved to be wrong.