Phaeophyscia orbicularis (Neck.) Moberg
Thallus foliose, usually rosette-shaped, 3-5 cm diam., composed of long palmate lobes, 1-1.5 mm wide, upper surface with highly variable colours (numerous morphotypes have been described), bright green, pale grey greenish when moist (and then markedly different from Physcia), pale grey brownish, grey-greenish, beige, brownish, brown-black when dry, sometimes tinged orange towards the center in necrotic sections, covered with laminal and marginal soralia, yellow-greenish, grey-greenish, grey-bluish, lower surface blackish with numerous simple rhizines, dark towards the center and whitish when they jut out from margins (as an old 'tooth brush'). Apothecia very rare, urn-shaped at first, then sessile, 1-2 mm diam., disc rough, brown-reddish then brown-black, exciple smooth, initially folded then wavy, concolourous to the thallus or paler. Ascospores brown, ellipsoid, 1-septate, 17-26 x 7-11 µm. Pycnidia frequent. Medulla K- but orange spots are K+ purple. Quite common on bark of main branches and trunks of more or less isolated trees, sometimes on concrete, neutral or calcareous rocks. Not to be confused with Physcia caesia of which the thallus is paler, the lobe upper surface is markedly flecked, without rhizines exceeding margins, with Physcia dubia of which the lower surface is whitish. N.B. Specimen growing on bark of deciduous trees with soralia and minute whitish cilia on lower surface (notably towards margins) would be refered to Mediterranean species Phaeophyscia hirsuta; specimen with minute whitish cilia and without soralia may be refered to Phaeophyscia ciliata. N.B. Sometimes parasited by Buelliella physciicola.