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; able to cover very large surfaces and therefore conspicuous even from far away. Apothecia unknown. Photobiont : chlorococcoïde. C-, K+/- orange, KC+/- red, Pd-. Not especially maritime, on protected and shaded surfaces of large rocks, notably on 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.