Verrucaria ochrostoma (Borrer ex Leight.) Trevis.

    Thallus crustose, in general well delimited but prothallus hardly visible, areolate, areoles plane or slightly convex, old specimen cracked, greyish, grey-ochre, grey-brown. Perithecia totally immersed, not visible excepted apex, more or less convex, black, involucrellum absent. Ascospores ovoid, simple, colourless, 18-24 x 9-13 µm. Chemical spot tests negative. Rare, on calcareous nutrient-rich rocks and stones, and mostly, in our prospection area, on mortar of walls of old churches where the specific grey  colour  makes the colonies hardly visible on cement and mortar. See Verrucaria viridula, a more common species, brown or tinged greenish.*