Acrocordia salweyi (Leight. ex Nyl.) A. L. Sm.

   Thallus: crustose, thin sometimes hardly visible, ± immersed in substratum,smooth to slightly granular, or warted,  whitish, greyish,  to pale brownish grey. Perithecia 0.7-1.5 mm diam., one quarter immersed in thallus, spherical, sometimes troncated or flatenned top, black, leaving a black scar or cupule after falling down. Asci  with top displaying a characteristic 'meniscus-like' or 'button-like' structure. Spores uni-septate, ellipsoid, with perispore making spores finely punctated,  20-35 x 10-15 µm. Photobiont : Trentepohlia. Chemical spot tests negative. On soft calcareous rocks and especially mortar of humid old walls in our prospection region.  See also Acrocordia macrospora strictly 'marine' and on acid substrata. Some specimens may resemble Acrocordia conoidea  with pinkish thallus, but the perithecia are  conical and the spores are smaller and growing on calcareous substratum. N.B. On the field it might be difficult to discriminate with Verrucaria muralis.