Clauzadea immersa (Hoffm.) Haffelner & Bellem.

     Endolithic crustose thallus difficult to differentiate from the substrate, whitish, pale greyish, pale ochraceous, sometimes with a blackish prothallus. Apothecia lecideine, 0.5-0.8 mm in diameter, deeply buried in the thallus and in a "pits" (clearly visible in the form of a cupule when the apothecia disappears), flat disk, reddish-brown, reddish-black when wet but becoming black to blackish when dry, sometimes pruinose with bluish grey, margin not very distinct, persistent. Spores elliptical, colourless, simple, with a gelatinous and finely punctuated perispore, 10-16 x 6-9 µm. Photobiont: Chlorococcoide. C-, K-, KC-, P-. Species occurring on the more or less inclined walls of hard limestone rocks, not especially maritime but relatively frequent on Mediterranean limestone maritime cliffs.

N.B. Appearance of saxicolous and calcicole Verrucaria but these latter species have perithecia and not apothecia.

_ Not to be confused with Rinodina immersa with small and non-pruinose apothecia and different spores.