Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: irregular to orbicular, up to 5 cm diam., ± firmly adnate lobes: mostly narrow, sometimes broader and overlapping, but usually c. 1 (-2) mm wide, convex and distinctly discrete, eciliate upper surface: gray to dark gray, usually white maculate and ± pruinose, sorediate soredia: in marginal, well delimited, semicircular to upwardly curved or labriform soralia (sometimes ± helmet-shaped) situated in the lobe sinuses upper cortex: paraplectenchymatous medulla: white lower cortex: proso- to indistinctly paraplectenchymatous lower surface: white to graphite gray or brownish, of the same color or darker than the lower surface, with few rhizines Apothecia: ± abundant, usually to 1 mm diam, rarely larger; margins: sometimes dissolved into soredia; disc: often with a whitish pruina ascospores: brown, 1-septate, Pachysporaria-type, (16-) 19.5-24 (-25) x (7.5-) 8.5-11 (-14) µm Pycnidia: not common, immersed conidia: subcylindrical, 4-6 x 1 µm Spot tests: cortex and medulla K+ yellow, C-, KC-, P+ yellow Secondary metabolites: upper cortex with atranorin; medulla with atranorin, zeorin and some unknown triterpenes. Substrate and ecology: growing on branches of trees in fairly open situation World distribution: scattered localities in South America Sonoran distribution: so far known from only two localities in the Sierra Madre Occidental region of Sonora. Notes: In its typical appearance P. rolfii is easily recognized by the semicircular soralia in the lobe sinuses and the short, widening and white maculate lobes.