Verrucaria internigrescens (Nyl.) Erichsen

     Thallus crustose, superficial, non-subgelatinous, uneven, more or less cracked, whitish or dull-whitish, pale grey or light brown-white, blackish hypothallus sometimes visible below areola, or as a line separating mosaics of adjacent conspecific thallus. Abundant black perithecia, conical, irregular, forming projections 0.35-0.75 mm diam., typically covered at their base by the dull-whitish thallus on ca. 1/3 of heigth. Ascospores oblong-ellipsoid, simple, 19-25 x 9-12 µm. On damp siliceous rocks, sometimes shaded, in the xeric-supralittoral zone on seashores, often in combination with other 'black' lichens. Rare in our prospection area, or understated, unperceived despite its dull-whitish or pale specific thallus, or also mistaken for Verrucaria aethiobola or Verrucaria muralis  misplaced near the seashores (but without black prothallus in case of mosaics).

N.B. Reports of Verrucaria marinomuralis in French Brittany are likely to be Verrucaria internigrescens.