Xanthoria parietina  

Thallus to 15 cm diam., often forming extensive patches, forming ± regular,  appressed, somewhat wrinkled rosettes, usually yellow-orange in full sun but frequently ± grey or greenish in shade. Lobes ± overlapping, plicate, broadened towards the apices, indented, the apical parts 1-3 mm wide, rounded or somewhat notched and ± flat; coarse, flat, subsquamulose to ligulate lobules sometimes present towards the centre of the rosette, usually scattered, but occasionally abundant, apparently the result of regeneration.
Anamorph: conidiomata pycnidia, laminal, immersed in hemispherical warts, inconspicuous, generally concolorous with the thallus, multilocular. Conidiogenous cells lining the locules, ± barrel-shaped, proliferating percurrently. Conidia 2.5-4 × 1-1.5 μm, ellipsoidal, hyaline, aseptate, without a gelatinous sheath.
Teleomorph: ascomata apothecia, usually numerous, to 4 mm diam., scattered to clustered, sessile to peltate (sometimes ± stalked when on twigs), orbicular to contorted, concave when young, becoming flat when mature, with a slightly raised, smooth, concolorous thalline exciple; old apothecia on moribund thalli becoming convex and immarginate. Epithecium golden, granular, K+ purple. Hymenium 50-60 μm in height, staining K+ purple in the uppermost 12-20 μm. Hypothecium colourless. Interascal tissue of loosely packed, coarse septate paraphyses to 2.5 μm diam. copiously branched near the apex, the apical cells swollen to 6-7 μm diam., capitate, K+ purple. Asci clavate, 8-spored. Ascospores arranged biseriately, (10-) 12-16 × (6-)7-9 μm, ellipsoidal, polarilocular, hyaline, thick- and smooth-walled, without an epithecium, gelatinous sheath or appendages.