Distribution: N - VG, Ven. S - Pugl (Nimis & Tretiach 1999).
Description: Thallus crustose, episubstratic, rather thin (0.1-0.2 mm), continuous to more often cracked, dark brown to black, usually somewhat shiny when dry, subgelatinous when wet, often covering large surfaces. Cortex poorly defined, with a brown pigment in upper part; photobiont cells arranged in vertical rows; medulla with punctiform to column-like, carbonaceous structures that sometimes reach the surface. Perithecia black, immersed into 0.4-1 mm wide thalline warts, the uppermost part projecting and naked, mostly flat-topped. Involucrellum thick, often reaching to base-level; exciple dark in upper part, colourless in lower part; hamathecium of periphyses and periphysoids, interascal filaments absent; hymenial gel hemiamyloid, I+ red (I+ blue at very low concentrations of I), K/I + blue. Asci (6-)8-spored, clavate, I-, fissitunicate, the wall thickened above, with an ocular chamber, dehiscent by extrusion of an endotunica to form a delicate rostrum, Verrucaria-type. Ascospores 1-celled, hyaline, ellipsoid, 12-15 x 7-9 μm. Photobiont chlorococcoid. Spot tests: thallus and medulla K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a rather poorly known species of maritime, mostly calcareous rocks in the supralittoral zone. See also note on H. amphibia.