Chrysothrix chlorina (Ach.) J. R. Laundon

    Thallus leprose, granular, granules 0,01-0,3 mm diam., forming a thick continuous crust more or less cracked, bright yellow, yellow-greenish, lemon. Apothecia unknown. Photobiont : chlorococcoïde. C-, K+/- orange, KC+/- red, Pd-. Not especially maritime, coming beneath overhangs and on the sheltered and little-sunny faces of the large rock masses, in particular the walls of Armorican sandstone.

N.B. Difficult to distinguish from Chrysothrix candelaris although the latter grows mainly on bark and seldom on rocks.

_ Also watch out for Psilolechia lucida with a smaller and generally fertile thallus that comes in darker and more humid places and out of direct light.