E-Flora BC: Electronic Atlas of the Flora of British Columbia

General:
Medium to large stratified foliose lichens, corticate above and below, sorediate or not, lobes closely appressed, elongate, averaging to 0.3–0.5 mm wide, thin. Upper surface pale yellowish green, dull. Lower surface pale to black, apparently white-pruinose, bearing scattered, short, simple rhizines. Medulla white. Photobiont green.Apothecia located over upper surface, disc brown; spores simple, ellipsoid, colourless, 8 per ascus. Over acid rock in arctic-alpine to boreal localities.

Notes: Arctoparmelia consists of four species worldwide, all of which occur in B.C. For points of distinction with similar species in other genera, see the descriptions under Xanthoparmelia.

Species description:
Thallus sorediate or apparently sorediate AND Upper cortex soft and eroding; soredia more or less diffuse

OR

Thallus lacking soredia AND
Upper cortex soft and eroding; lobe tips generally downturned

Reactions:
Medulla KC+ pinkish.

Contents:
Alectoronic acid, alpha-collatolic acid, atranorin, (and unidentified purple pigment).