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

Thallus: squamulose to crustose, forming small irregular rosettes up to 2 cm across, lobate lobes: elongated, filiform or canaliculate, irregularly stellate center: with granulose areoles upper surface: dark olive to blackish, sometimes becoming densely isidiate lower surface: dark, resting on a dark, blackish hypothallus; prothallus: absent Apothecia: semi-immersed to sessile, laminal, lecideine, up to 1 mm wide; disc: black, open, at first depressed, later convex; exciple: dark colored; epihymenium: dark; hymenium: up to 100 µm high, amyloid; paraphyses: distinctly septate, sparingly branched, apical cells pointed or thickened; subhymenium: brownish asci: 8-spored, sometimes fewer ascospores: 2- or 4-celled, hyaline, ellipsoid to broadly ellipsoid, (11.5-) 15-18 (-21) x (4.5-) 5.5-7 µm; walls: thin Pycnidia: immersed, marginal, ± globose, up to 0.15 mm wide conidia: cylindrical or party dumbbell-shaped, hyaline, 4.5-8 x 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on moist, siliceous rock World distribution: Northern Hemisphere Sonoran distribution: mountains of SE and eastern Arizona and the Sierra Madre Occidental in Chihuahua. Notes: The species is rather variable in morphology and sometimes hard to separate from Placynthium nigrum as both species possess a thick hypothallus and often have a conspicuous blue prothallus. Placynthium nigrum is distinguished on account of the marginal squamules that are small and irregular in shape. Although the names Collema asperellum Ach. and Parmelia aspratilis Ach. both date back to 1810, recent authors (Nimis 1993, Purvis et al. 1992, Santesson 1993, Wirth 1995) give Placynthium asperellum (Ach.) Trevis. as the correct name for that species.