Arctoparmelia (aka “Ring Lichens”)
Substrate: on siliceous rocks usually in the open.
Range: Boreal & arctic regions. Mainly arctic & alpine.
Description: Yellowish Green; Similar to Xanthoparmelia except lower surface is instead velvety, ivory white to gray, black, or purplish; often narrower lobes. Narrow-lobed (0.3 – 0.5 mm across), dull greenish yellow foliose lichens, commonly forming concentric rings of radiating lobes, with the thallus dying in the center of the rosette; lower surface with a dull, white or pale tan to very dark gray cortex; rhizines unbranched & scattered. Photobiont green (Trebouxia?).
Apothecia: Lecanorine, with brown disks & thallus-colored margins.
Spores: Colourless, 1-celled, ellipsoid, 8 per ascus.
Chemistry: Cortex PD-, K+ yellow, KC + gold, C- (usnic acid with atranorin).
Lookalikes: Xanthoparmelia but differing in chemistry & a lower surface is different. Xanthoparmelia grows in many places Arctoparmelia does not. Xanthoparmelia super-ficially resembles Arctoparmelia but usually has a shiny upper surface, a brown to black, shiny lower surface with branched rhizines, & an entirely different medullary chemistry.
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