pale gray upper surface with wrinkly, maculate surface, pale lower surface with mostly pale (with some dark rhizines on edges) rhizines, abundant apothecia with blue/dark gray centers and wrinkly edges, upper surface K+yellow, medulla K+ pale yellow (second photo shows pale medulla, the next one shows medulla with K + Y next to green algal layer) on old Valley Oak bark Carlberg (2016 draft) key 1b) fruiting body not mushroom 2b) stratified thallus interior 3b) lower surface different than upper 4b) thallus with rhizines 5b) grass-green algal layer >> stratified green algae foliose 1b) lobes solid 2b) lower surface not cottony 3b) not above 4b) thallus white/gray 5b) thallus white/gray 6b) foliose, on bark 7a) lobes < 1.5 mm >> Narrow lobed foliose 1a) upper surface K+Y, pale gray 2b) thallus pale gray, lower surface white 3b) lower surface corticate, pale, upper surface lacking isidia McCune & Geiser (2014) key 1b) lobes without cilia 4b) soredia absent 8a) on bark 9b) thallus not pruinose 10a) medulla K+Y P. aipolia (apothecia covered in pruina)