Physconia subaquila (Nyl.) Cl. Roux

     Leaf-like thallus strongly adherent to its substrate, formed of very indented lobes overlapping more or less, to then form a very thick thallus in certain places (in cushions), upper surface of the lobes smooth and shiny, greyish, brownish, grey-brownish in time dry, greenish in water, olive-brown, greenish in wet weather, very strongly pruinescent white especially at the ends of the lobes which appear frosted, blackish underside with simple, black rhizines. Very rare lecanorine apothecia, concave flat disc, powdery, bluish-gray, very thick margin sometimes with "daisy"-shaped outgrowths. Spores 1-septate in "capsule", dark brown, 25-40 x 15-20 µm according to our measurements. Photobiont: Trebouxoid. Medulla white, C-, K-, KC-, P-. Rare species typically found on the siliceous coastal rocks of the supralittoral zone around the Mediterranean, particularly in Corsica.

N.B. Not to be confused with the saxicolous forms of Physconia venusta saxicoles which are fertile and whose underside is whitish and not maritime.