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 hohogenous thallus, and also ellipsoid ascospores.*