Parmelia saxatilis (L.) Ach.Thallus foliose, heteromerous, dorsiventral, rather loosely attached, forming 4-20 cm wide, mostly regular rosettes. Lobes sublinear, contiguous, elongate, separate, flat, 1.5-2.5(-3.5) mm wide, with truncate apices, rarely lobulate. Upper surface grey (to brown in exposed situations and at lobe tips), smooth to foveolate, somehow shiny, rarely slightly white-pruinose in marginal parts, with numerous, mostly apical or marginal, elongate-linear, rarely weakly anastomosing, white pseudocyphellae. Isidia cylindrical, simple to coralloid, often darkened at tips, scattered to clustered but not developing in lines along the pseudocyphellae, mainly laminal and most abundant in central parts of thallus. Lower surface black, with simple to furcate, black rhizines present also along the margins. Upper cortex paraplectenchymatous, of 2-6 layers of densely packed cells, with a usually non-pored epicortex, the cell walls with isolichenan; medulla white; algal layer continuous; lower cortex paraplectenchymatous, thinner than upper cortex. Apothecia rare, lecanorine, 2-8 mm across, with a brown disc and a usually isidiate thalline margin. Epithecium brownish; hymenium and hypothecium colourless. Asci 8-spored, clavate, <i>Lecanora</i>-type. Ascospores 1-celled, ellipsoid, hyaline, (11-)13-15(-18) x 6-8(-11) µm. Pycnidia black. Conidia cylindrical to bacilliform, 5-8 x c. 1 µm. Spot tests: upper cortex K+ yellow (but often slowly turning orange-red due to medullary substances), C-, KC-, P- or P+ faintly yellow; medulla K+ yellow turning orange-red, C-, KC-, P+ orange-red, UV-. Chemistry: upper cortex with atranorin and chloroatranorin; medulla with salazinic acid (major) and consalazinic acid (minor), and often traces of lobaric and protocetraric acids; fatty acids (lichesterinic and protolichesterinic acids) absent. 