Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.

Notes: Psorula differs from Psora mainly in the following characters: lichenicolous life habit, green pigments in the apothecium and pycnidium, absence of anthraxquinones from the epithecium, absence of calcium oxalate from the hypothecium, sessile pycnidia, intricately branched conidiophores, and pleurogenous, narrowly ellipsoid pycnoconidia (see Timdal 1984a). Because the genus is now regarded as monotypic, it would be repetitious to have a separate generic description. Initially a second species, P. scotopholis (Tuck.) Gotth. Schneid. (Schneider 1979), was included in Psorula, but Timdal (1984a) placed that species in Lecanora.