Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Mycelium: I- or I+ blue Apothecia: superficial, 120350(-700) µm in diam. disc: black, frequently epruinose, rarely densely covered by yellow pruina, at the beginning often flat, later generally becoming strongly convex epihymenium: dark greenish brown, K+ green hymenium: hyaline to pale brown, K+ green hypothecium: brown, K asci: elongate ellipsoid to clavate, 8-spored ascospores: brown, verrucose, 1-septate, cells slightly unequal in width, 11-14 x 4.5-6 µm Pycnidia: black, partly immersed conidia: hyaline, obpyriform to ellipsoid, c. 7 x 5.5 µm. Hosts: thallus and apothecia of Usnea species, frequently overgrowing galls induced by Biatoropsis usnearum World distribution: known from all continents, except Antarctica Sonoran distribution: Arizona and California north of the region. Notes: The Abrothallus material on Usnea is variable. Ascomata are sometimes applanate, even when mature, whilst in other specimens they soon become strongly convex and almost subspherical. The mycelium appears to be give a positive blue reaction with I in some specimens, but not in others. As long as no modern revision of the genus is available, I prefer to call all specimens on this host A. usneae.