Punctelia borreri (Sm.) KrogThallus foliose, heteromerous, dorsiventral, forming 5-10 cm wide rosettes, sorediate. Lobes tightly adpressed, 5-10 mm wide, rounded and ascending at apices, eciliate, grey, with numerous punctiform, white pseudocyphellae giving rise to orbicular, up to 0.7 mm wide, laminal, white soralia. Lower surface black in central part, dark brown at margins, with simple rhizines which become more sparse at margins. Upper cortex paraplectenchymatous, of 2-6 layers of densely packed cells, with a non-pored epicortex, the cell walls with isolichenan; algal layer continuous; medulla white; lower cortex paraplectenchymatous. Apothecia very rare, lecanorine, with a brown disc and an often sorediate thalline margin. Proper exciple thin, colourless; epithecium brownish; hymenium and hypothecium colourless. Asci 8-spored,clavate, <i>Lecanora</i>-type. Ascospores 1-celled, hyaline, broadly ellipsoid, 15-18 x 12-15 µm. Pycnidia black, laminal. Conidia short-filiform, 5-7 x 1 µm. Photobiont chlorococcoid. Spot tests: upper cortex K+ yellow, C-, KC-, P- or P+ very faintly yellow; medulla K-, C+ pink, KC+ pink, P-, UV-. Chemistry: upper cortex with atranorin and chloroatranorin; medulla with gyrophoric acid (major) and fatty acids. 