Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: squamulose-foliose, forming irregular rosettes up to 4 cm diam., resting on an inconspicuous, thin, blackish hypothallus lobes: somewhat enlarged, up to 3 mm wide and 150 µm thick upper surface: gray-blue to brownish, lobulate, lacking isidia or soredia isidia: coralloid to claviform, marginal upper cortex: paraplectenchymatous, two cells thick Apothecia: rare, up to 1.5 mm wide; disc: brownish, sometimes with adhering isidia; proper exciple: distinctly paraplectenchymatous; hymenium: I+ blue, up to 100 µm high asci: with apical amyloid tubes, 8-spored ascospores: simple, colorless, ellipsoid, smooth, 14-16 x 5-7 µm Spot test: all negative Secondary metabolites: none detected. Substrate and ecology: on bark, commonest on oaks, about 2000 m World distribution: Central America and Mexico Sonoran distribution: montane oak forests in Mexico (Sonora, Chihuahua and Sinaloa). Notes: This species is characterized by its numerous claviform isidia, and is much larger and more foliose than P. triptophylla which in this region is only found on rocks and at higher altitudes. Parmeliella pannosa has flattened lobules and a much more prominent hypothallus, and is mainly found at lower elevation (rarely above 1500 m).