Life habit: lichenized (mutualistic with algal photobionts) thallus: peltate, umbilicate thallus: continuous, diffuse, effuse [th] morphol substructures (eg areoles, squamules): distantly discontiguous primary photobiont: present secondary photobionts (eg in cephalodia): absent primary photobiont: chlorophytaceous – trebouxiaceous, chlorococcoid.

substrate: rock – siliceous, siliciferous, acidic.

Thallus small, to 2 cm broad, mono- or polyphyllus, the margins thin, slightly incised; the umbo raised, raised ridged and frosty pru-inose; upper side smooth, slightly reticulate veined, with minute papillae, dark brown to black; underside verrucose, black, with flat or rounded rhizines, which are attenuate. Apothecia few to numerous, adnate, to 1 mm broad; disk black, flat, the margin irregular; paraphyses unbranched, capitate, to 2.5 µ; spores 8, simple, hyaline, 5-7.6 x 11-14 µ.

Reactions: K —, C + red medulla, KC + red, P —.

Contents: contains gyrophoric acid (Krog 1968), unlike the other species of Agyrophora.

A species of acid rocks, this appears to be a species of the western mountains. The type locality is near Lake Peters on the north slope of Alaska and it ranges south into the mountains of Washington. Alstrup (1979) recently reported it from Narssaq, Greenland.