Pleopsidium flavum (Bellardi) Körb.

     Thallus crustose, areolate with mat and not shiny (felted surface under magnifying glass) convex areoles, more or less wrinkled and rough in the center and very distinctly bordered by convex lobes, yellow, bright yellow, lemon yellow sometimes a little greenish yellow. Numerous apothecia, lecanorins, at first embedded in the thallus then more or less sessile, 0.5-1.5 mm in diameter, flat disc, yellow-brown, rim concolor to the thallus, persistent. Largely utriform asci containing a large number of spores (100 to 200), 55-65 x 25-30 µm according to our measurements. Spores colourless, elliptical, sometimes with a perispore, 3-6 x 2 µm according to the literature, 3-5 x 2 according to our measurements. Colline and mountain saxicolous species coming on vertical faces protected from direct rains from large siliceous rocks.

N.B. Easy to confuse with Pleopsidium chlorophanum, the apothecia disc of which is convex and with a non-persistent rim.