Thompson, J. 1984. American Arctic Lichens: The Macrolichens.

Thallus medium to large, the lobes to 3 cm broad, rounded; upper side with large and small reticulate pitting, pseudocyphellate, the pores few or many, mainly on the ridges, yellow to yellowish-tan with the edges black; lower surface jet black, smooth or wrinkled, brown toward the margins, lacking rhizines. Upper cortex 16-26 ¡x thick, densely filled with minute brownish crystals; medulla white or partly lavender especially in older parts, 93-248 µ thick; lower cortex 12-22 µ thick. Apothecia rare, described by Culbersons from Japanese material, submarginal to laminal, to 2.4 cm., disk brownish black; hymenium hyaline 52-70 µ, hypothecium 1 + lavender, proper exciple I-; spores 8, ellipsoid, 8-13x5-8 µ; pycnidia rare, marginal; conidia 5-6.5 x 1 µ.

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

Contents: usnic acid and atranorin in upper cortex, alectoronic acid± a-collatolic acid in medulla.

This species grows over boulders and plant debris and humus, occasionally on soil in tundras. A member of the Beringian Element in the Arctic, it ranges into Finland in Europe and in North America east to Baffin Island. It does not appear to range southward in the Rocky Mountains, remaining arctic only.