Diploschistes caesioplumbeus (Nyl.) Vain.
Diploschistes actinostomus var. caesioplumbeus (Nyl) J. Steiner
Thallus crustose, rather thick and with an aspect similar to Aspicilia, more or less smooth and shiny, areolate, cracked, with a conspicuous characteristic colour: lead-grey to blue-grey, edged by a dark-grey or pale grey prothallus. Apothecia 0.1-0.2 mm diam., immersed in areoles, resembling to perithecia (or like a wheel with tire), sometimes several per areole, leaving a small opening depressed, with marginal excipular hairs visible as a ciliate fringe or radiating ribs. Ascospores broadly ellipsoid, dark brown, muriform, 30-45 x 11-24 µm. Photobiont : Trebouxia. K-, C+ red, KC+ red, Pd-. On siliceous rocks near the sea shores in the well-lit supralittoral zone, this species is a parasite of other crustose lichens that are gradually replaced. Ascii (2)-4-8-spored (depending on aborted spores during further development), apex beak-shaped, 80-120 x 30-40 µm according to our measures. Ascospores broadly ellipsoid, colourless at first (sometimes I+ purple in lugol), then brown, muriform, 5-9 transversal septa and 2-4 longitudinal, 30-45 x 11-24 µm according to literature, 27-45 x 20-25 (30) according to our measures. Photobiont: Trebouxia. K+/- yellow, C+ red, KC+ red-orange, Pd-. Parasite of other crustose lichens during its early stages of its development, extending to the whole host thalli on siliceous rocks in the foreshore well-lit supralittoral zone. According to our observations, the most frequently parasited species is Tephromela atra and Lecanora gangaleoides (see the pictures of Diploschistes caesioplumbeus forme parasite de Tephtomela atra et de Lecanora gangaleoides). It is often competing with Lecanora sulphurea that, when young, is itself sometimes a parasite of Tephromela atra, but it seems that in the course of this competition, Diploschistes caesioplumbeus may become itself a prey of Lecanora sulphurea (see Lecanora sulphurea vs Diploschistes caesioplumbeus). N.B. This taxon was sometimes named Diploschistes actinostomus that in fact is a paler taxon, greyish but not grey-blue, with smaller ascospores: 20-40 x 10-15 µm (but the distribution curves of ascospores sizes of these 2 taxa overlap!), not especially coastal (but not rare in this habitat) and not parasite at first. All the intermediate forms between these two taxa exist.