Holtanhartwig J. 1991. A Revision of the Lichens Bryonora-castanea and Bryonora-curvescens. Mycotaxon 40: 295-305.
Thallus indistinct or forming a thin, whitish granular crust on the substrate. Apothecia 0.5-1.1 (-2.0) mm i (sic) diam., when old often crowded and irregular; disk usually pruinose, pale reddish brown to medium reddish brown; with a concolorous or paler margin; later often weakly convex and bumpy, with somewhat down-turned margin; cortex without internal crystals (polarized light!), K-, KI+ faintly violet; medulla K-, KI+ faintly violet. Epithecium yellowish brown, K-, N-. Spores ellipsoid to cylindrical, sometimes curved, simple, or sometimes up to 2-septate, (19-) 20-26.5-33 (-39) X (5-) 5-6-7 (-8.5) µm.
Chemistry: Isousnic acid.
Ecology: Growing on mosses, in arctic and alpine regions.
Distribution: See fig. 4D.
Bryonora septentrionalis is recognized by its long spores, the occurrence of isousnic acid, and by the often densely pruinose and slightly convex apothecial disks.
The four species are apparently closely related, but may, with some experience, be distinguished morphologically. Although overlapping, each species have a high degree of internal continuity in spore size, and the results of spore analyses fit well with a classification into four species based on morphology.
The KI reaction in the cortex and medulla of B. pruinosa and B. septentrionalis may sometimes be very faint and is not a good diagnostic character.
All four species occur above or north of the timberline, and have quite similar distribution areas. Bryonora septentrionalis has the most northern distribution area, apparently lacking in the Alps and in the southern parts of Greenland. Bryonora pruinosa is apparently lacking in Svalbard, and occurs at somewhat lower altitudes than the other three species. I have seen rather few collections of Bryonora from the Alps, however, and can not definitely state that B. septentrionalis is missing there.
The four species grow on plant debris or dying mosses and lichens. Bryonora curvescens is always growing on Andreaea and Grimmia, whereas B. pruinosa often is growing on dying lichens. The other two are apparently less specific in choice of substrate.