Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.

Thallus: endolithic Apothecia: black, dispersed, in pits or not, minute 0.2-0.3(-0.5) wide disc: reddish black to black, minute, c. 0.1 wide deeply immersed and barely visible, plane, surficially carbonized, becoming umbonate and slightly gyrose margin: prominent, relatively thick, eventually splitting true exciple: parathecium: 30-45 µm thick, outer layer black, c. 20 µm wide, inner layer ±brown epihymenium: black, conglutinated, c. 15 µm thick hymenium: hyaline to slightly yellow, 50-80(-100) µm tall, conglutinate paraphyses: (1.8-)2-2.5(-2.9) wide, septate, broadened apices hidden in carbonization subhymenium: hyaline to slightly yellow, c. 15 µm thick hypothecium: indistinct asci: broadly clavate, c. 40 x c. 20 µm, 100+-spored ascospores: hyaline, simple, broadly ellipsoid, 3.5-5.5 x 2-2.5 µm Pycnidia: not observed Secondary metabolites: none detected. Substrate and ecology: on carbonaceous rock (often soft) World distribution: Europe and North America (Canada, Montana, White Mountains in California) Sonoran distribution: Arizona and southern California (north side of San Bernardino Mountains). Notes: The small size of its apothecia combined with its spore size is distinctive for P. urceolata. In contrast, P. cyclocarpa is not only larger but has a convex, gyrose disc, that is not umbonate in specimens I have seen. Polysporina urceolata has a carbonized disc that often becomes umbonate. It can potentially be confused with the small-spored P. simplex.