Physcia tribacia (Ach.) Nyl.
Thallus foliose, usually irrgular in outline, forming lying irregular or rounded tufts, to 4-6 cm across, potentially able to merge with other conspecific colonies, lobes 1-2 mm wide, apices twice incised giving a wrinkled aspect, upper surface minutely pruinose, grey-whitish, pale greyish, grey-yellowish isidia -and later soredia- covering the lobe apices. Apothecia very rare and most frequently absent, underside whitish to pale brownish. Apothecia very rare and most often absent, 1-1.5 mm diam.. Ascospores broadly ellipsoid, 15-24 x 9-11 µm. Pycnidia more or less abundant. Cortex : C-, K+ yellow, KC-, Pd- ; Medulla : C-, K-, KC-, Pd-. On rocks and nutrient-rich bark of wayside old trees, around chapels near the seashore or within areas under oceanic climate influence.
N.B. Sometimes difficult, or even impossible to differentiate from Physcia dubia except by performing a microscopic examination (lower paraplectenchymal cortex). Cf. Physcia tribacioides, the globular soralia of which are whitish, laminate and scattered throughout the thallus.