Physcia aipolia (Ehrh. ex Humb.) Fürnr.

    Thallus foliose, rosette-shaped, to 10 cm diam., lobes radiating, 1-2 mm wide, upper surface conspicuously flecked (suggesting a snowy sky) due to whitish spots (pseudocyphella), isidia and soredia absent, pale greyish, pale grey-greenish, with a faint blue tinge when dry and a green tinge when moist (green when re-hydrated), lower surface whitish to pale brown, simple or branched rhizines (not to be confused with cilia when present towards the lobe margins). Apothecia usually numerous, clustered towards the center, 1-3 mm diam., disc flat at first, then convex, dark brown to black, occasionally greyish owing to pruine, exciple thick, concolourous to the thallus. Ascospres brown, ellipsoid, 1-septate, 18-24 x 7-10 µm. Pycnidia frequent. Cortex and medulla: K+ yellow.  Common on trunks and main branches of deciduous trees, rare on rocks, notably near the seashore. Not to be confused with Physcia leptalea which has numerous cilia towards lobe margins and with Physcia stellaris of which only the cortex is K+ yellow and the lobe surface is not flecked.*