foliose, irregularly spreading and loosely attached; lobes solid, nodulose, 0.5-1 mm broad, terete or flattened when on stone; upper side pale gray, ashy gray, brown or black, maculate, distinctly areolate with discontinuous patches of cortex interspersed with black cracks and lines; underside black, brown toward the tips; lacking soredia or isidia. Apothecia
rare, to 5 mm broad; disk
dark brown, thalloid margin thin, entire; spores
subglobose to broadly ellipsoid, 10-12 x 8 μ.
Reactions: cortex K+ yellow; medulla K— , KC+ red, C— , P+ orange in layer close to cortex in apices only or P— , I— .
Contents: physodic acid, atranorin, with accessory protocetraric acid.
This species grows on rocks and over mosses in places with winter snow cover. It is arctic and northern boreal, circumpolar, in North America ranging south to New Mexico in the west, and the Adirondack and White mountains in the east.