Arthonia calcarea forma

 

    Thallus crustose, rather thick and in general distinctly visible, often circular, reaching 2-5 cm diam., smooth to rimose, white, whitish, chalk-white, white-greyish. Apothecia lirelliform, simple, placed in all directions in small clusters or stacks of 3-5 mm diam., black. Ascospores slightly clavate, 3-septate, 16-20 x 4-6 µm. C-, K-, KC-, Pd-. Common in our prospection areas near the seashore on cement and mortar of walls, sometimes on abestos. N.B. Belongs to the Arthonia (Opegrapha) calcarea taxon group, for which the taxonomical ranking varies from morphotype to valid species according to authors. This taxon, common along the shore, was probably collected under the name Opegrapha chevallieri by ancient authors.