areolate, the areolae dispersed or in small groups, to 2 mm broad, rounded or crenulate, rarely angular, flat or uneven, dull, sometimes shining, yellowish, pale brown, or seldom rust-brown; underside pale. Apothecia
immersed, usually 3-7, rarely 1 or 2, per areola; disk
to 0.4 mm broad, dark brown or black, even, slightly roughened, sunken or level with thallus; proper exciple
well developed, 10-20 µm below, widening to 50 µm above, hyaline or pale yellow; hypothecium
dense, I+blue; epihymenium
brownish yellow; hymenium
125-200 µm hyaline I+ reddish or yellowish brown; paraphyses
1-1.5 µm, the upper cells appearing submoniliform; spores very numerous, elongate or cylindrical, 3-4.5 x 1-1.5 µm.
Reactions: cortex K+ red, C—, P—, I-.
Contents: There are contradictory statements in the literature. Magnusson (1935b) mentioned rust-red crystals and a K+ red reaction, which would signify norstictic acid. Follmann & Huneck (1971b) found gyrophoric acid and traces of lecanoric acid. These would have yielded C+ red, K— reactions, and their material must have been mislabeled. Mitchell (1965) listed usnic acid, but this is very unlikely in this genus. Hawks worth (1972) found traces of norstictic acid, and this would agree with the Magnusson report.
This species grows on acid rocks, on cliffs, boulders, and especially on rocks manured by birds. It is circumpolar subarctic and alpine. In North America it is reported south to Arizona, Texas, Colorado, the Great Lakes region, and Kentucky.