Xanthoria parietina forme isidiée.
Differs from the type by its small isidia (or isidioid excrescences), simple or spatula-shaped towards thallus center. Thallus greenish to grey-greenish, except sometimes yellow at lobe margins, apothecia scarce, uncompletely developed. Isidia towards thallus center frequently associated with a free green algae. Restricted to North faces of trunks of deciduous trees, never subjected to direct sun. Might be a form corresponding to Xanthoria parietina in limiting conditions of growth.