Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus ashy, greenish, brownish, or lacking, thin, scurfy; hypothallus brown-black or lacking. Apothecia tiny, 0.3-0.4 mm broad; flat to slightly convex; margin black, becoming excluded in some specimens but usually prominent; exciple brown-black; hypothecium brown-black; epihymenium brown; hymenium brown above, hyaline below; paraphyses loosely attached, septate, branched, tips brown-capitatc; spores 1-septate, brown, ellipsoid, small, 9-16 x 4-8 μm.
Reactions: thallus K-, C-, P-, I-.
This species grows on rocks. It is so close in structure to B. punctata that some authors consider it a saxicolous form of that species. It appears to be arctic-alpine in Europe, North America, and Greenland but with too few collections to be definite as to its true range.
Very close to this, and possibly the same species, is Buellia groenlandica Vainio from Turner Sound, eastern Greenland. Vainio described it as differing from B. punctata only in having the disk umbonate and the spores polarilocular. A full description of the type and only specimen of B. groenlandica was given by Lamb (1968, p. 80). The central umbo is not conspicuous externally and is visible only in sections. The spores arc distinctly polarilocular with a thick septum traversed by a pore, and the spores are 12-14 x 7-8 μm.
B. stigmatea should not be confused with B. stigmaea Tuck., a different K+ red (norstictic acid) species allied to B. aethalea, which is found in the eastern United States.