Cetrelia cetrarioides (Delise ex Duby) W. L. Culb. & C. F. Culb.

    Thallus foliose, 10-12 cm diam., loosely attached on and amongst mosses on trunks, made of lobes, rounded at apices, margin delicately edged by white-greyish soralia (sometimes laminal); upper surface smooth, pale grey-green when moist, glaucous to grey-whitish when dry, occasionnally with small brown spots; thallus lower surface center blackish, margin paler, often dotted with minute rounded pseudocyphellae and rhizines, blackish. Apothecia absent or very rare. Photobiont : Trebouxia. Cortex : C-, K+ yellow, P- ; medulla : C- or weakly pink, K-, KC- ou KC+ pale pink,  Pd-, I-, UV+ white-blue. Rare, amongst mosses on trunks of old trees in long-established oceanic woodlands.  See Cetrelia olivetorum s.l. since it is under that name that this species most often was collected.*