Phyllopsora rosei Coppins & James

      Thallus forming a relatively thick crust on its substrate, consisting towards the center of pubescent granules and towards the margin of scales 0.15-0.3 mm, swollen and more or less crenate, greyish, gray-glaucous in dry weather, green -bluish to typically emerald green in humid weather, prothallus white, cottony, often inconspicuous except at the tip of the squamules which appear cottony whitish. Apothecia absent or rare to infrequent in our climates, often grouped in small clusters, 0.3-1.5 mm in diameter, convex to tuberculate, sometimes fissured, pale brown to dark brown. Spores hyaline, narrowly elliptical, (0) 1 (3) times septate. Photobiont: trebouxioid. C-, K + / - yellow, P + red. Species found in humid oceanic forests on the bark of old tree trunks (Quercus) where it invades bryophytes. Similar species from the same habitat especially Megalaria pulverea do not have squamules towards the margin. N.B. Very similar to Biatora efflorescens and Biatora britannica but these latter species do not have scales.