Thallus greenish yellow to very bright yellow, becoming thick, verrucose-rugose or areolate with convex areolae. Apothecia to 3 mm, adnate with thin thalloid margin concolorous with thallus; disk blood-red, flat to convex, violet with KOH; hypothecium hyaline; epihymenium reddish brown, K+ blue-violet; hymenium hyaline below; paraphyses very coherent, tips thickened and darkened reddish; asci clavate; spores 8, 3-7-septate, cells cylindrical, hyaline, commonly curved or twisted, one end more tapered than the other, 35-55 x 3-5 μm.

Reactions: K—, C —, P—.

Contents: usnic and divaricatic acids constant, zeorin is accessory. My report (Thomson 1979) of barbatic acid is erroneous and based upon crystal similarities with the thamnolic acid.

This species grows on rocks, mainly noncalcareous, and in the open, sometimes in habitats with slightly greater moisture, as in rock streams in the Arctic. It is circumpolar arctic-alpine. It ranges south in North America to Volcan de Toluca in Mexico.

A pair of species of Ophioparma reach the Arctic. O. ventosa (L.) Norman is limited to Europe and has a K+ yellow reaction due to the presence of thamnolic acid. O. lapponica (Rásanen) Hafellner & R. W. Rogers is circumpolar and, lacking the thamnolic acid, is K—. Only the latter species occurs in the American Arctic. These species were removed from Haematomma by Rogers and Hafellner (1988) mainly by reason of the differing ascus types, Haematomma having a typical “Lecanora-type” ascus with an axial mass and ocular chamber in the tholus.