Arctoparmelia centrifuga (aka “Xanthoparmelia centrifuga” or “Concentric Ring Lichen”)
Range: Mainly arctic & boreal south to central British Columbia.
Description: Lower surface pale. Lobes flat to slightly convex, 1-2 mm wide, without soredia or isidia; lower surface white or almost white, with scattered dark rhizines.
Apothecia: Fairly common.
Lookalikes: The white lower surface distinguishes this lichen from the much rarer Arctoparmelia separata & Arctoparmelia incurva; both have a mouse-gray lower surface, & Arctoparmelia incurva produces large, irregular sorelia on the upper surface. Rarely, Arctoparmelia centrifuga lacks usnic acid & a gray instead of yellow-green, with the cortex reacting K+ yellow, KC-.
In the Arctic, Arctoparmelia centrifuga has been used as a source of red-brown dyes for wool.
Bibliography: Macrolichens of the Pacific Northwest, by Bruce McCune & Linda Geiser, Lichens of North America, by Brodo, Sharnoff, & Sharnoff
Database Entry: Distance Everheart 12-26-13