Heteroplacidium fusculum (Nyl.) Gueidan & C. Roux

    Thallus crustose, up to 10 cm diam., deeply and broadly cracked, areoles well separated, 0.5-1.5 mm across, flat or slightly convex, dark brown, brown-blackish; areoles crowded at first then coming apart at cracks, final aspect like dry mud. Perithecia hardly visible, almost totally immersed, black. Ascospores subglobose, 10-11 x 8-10 µm. Chemical spot tests negative. Thermophile, on hard limestone in well-lit hot locations. At first this species is a parasite of Aspicilia calcarea  but grows independently after.

_ Not to be confused with Verrucaria nigrescens that sometimes has the same colour but with smaller and not so separated areoles and consequently a more homogenous thallus, and also ellipsoid ascospores.