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 lacking soredia AND Upper cortex firm, never eroding; lobe tips only rarely downturned AND Lower surface grey or black toward thallus centre; northern B.C.

Reactions:
Cortex K+ pale yellow, KC+ yellow; medulla C+ slowly yellow, KC+ reddish.

Contents:
Alectoronic acid, atranorin and usnic acid.