Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus thick and knotted, continuous, rounded and piled up, white or yellowish white, smooth and shining, sometimes roseate or brownish, occasionally slightly pruinose, lacking soredia or isidia. Fertile verrucae like the thallus, the shapes from simple and hemispherical to conglomerate masses with many ostioles but the base narrowed, even forming multiperforate sheets. Apothecia immersed, ostioles usually black, sometimes with white border; hypothecium hyaline to brownish; epithecium hyaline or dark, K— or infrequently weakly K+ violet; hymenium hyaline to pink; asci cylindrical; spores 2 (occasionally 1, rarely 3 or 4), uniseriate, oval to cylindrical, double-walled, outer wall 1-4 μm thick, inner 5-19 μm, usually smooth, often with concentrically laminated ends (rarely rough or radially grooved), with irregular thickening of end wall, 160-245 x 38-75 μm.
Reactions: cortex K—, C—, KC— P—; medulla K+ yellow turning red, C —, KC —, P+ yellow turning yellow-orange.
Contents: thiophaninic acid (scant), norstictic acid, and connorstictic acid.
This species is very common on humus, soil, moss, and the soil at the edge of frost boils. It is circumpolar arctic.
This species is easily confused with P. subobducens but is distinguished by the color reactions and the content as well as by the weaker K+ reaction of the epithecium.