Diploschistes actinostomus  (Pers. ex Ach.) Zalhbr.

     Thallus crustose, 0.2-1 mm thick, markedly cracked, areolate, areoles 0.5-1.5 mm across, dull grey-whitish, pale grey, grey-blue but  seldom blue (see  Diploschistes actinostomus forme bleue), sometimes with darker sections, prothallus often distinct, blackish. Apothecia 0.2-0.8 mm diam., immersed in areoles, disc punctiform, flat, blackish, exciple with minute radial ribs (perithecia aspect). Ascii 4-8-spored. Ascospores broadly ellipsoid, colourless turning to grey-brown, muriform, 4-5-6 transversal septa and 1-3 longitudinal septa,  20-30 x 10-15 µm. Photobiont: Trebouxia. Cortex and medulla: K-, C+ carmine, KC+ carmine, Pd-. Medulla: I+ indigo-blue. Common, on siliceous rocks near the seashore in the well-lit supralittoral zone, scarce inland. Species close to Diploschistes caesioplumbeus that is strictly maritime and  parasite of other crustose lichens that are gradually replaced and notably Lecanora gangaleoides and Tephromela atra. Intermediate specimen may be found and hamper identification.