Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: squamulose, squamules: dispersed or adjacent, broadly adnate but usually the extreme edges slightly ascending, 2-4 mm wide, up to 0.4 mm thick, rounded or lobed, black-rimmed upper surface: brown, dull upper cortex: c. 40 µm thick, with or without a thin epinecral layer medulla: with many spherical cells (10-16 µm in diam.; algal layer: c. 70-120 µm high lower cortex: indistinct, composed of more densely packed spherical cells lower surface: dark brown to jet black throughout; rhizohyphae: hyaline, becoming slightly brownish, 5-6 µm thick Perithecia: up to 0.5 mm wide, broadly pearshaped; exciple: pale except for the ostiolum or darkening with age; periphyses: 35-45 µm long asci: cylindrical, 65-80 x 10-14 µm, 8-spored ascospores: uniseriate, ellipsoid, c. 11-14 x 5-6.5 µm Pycnidia: marginal, forming knob-like projections conidia: oblong-ellipsoid, 2.5-4 x 1.3-2 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: soil, mostly in inland sites at higher, montane elevations, descending to coastal scrubland in Baja California World distribution: South America (Andes), SW North America Sonoran distribution: SE Arizona, Sonora, Baja California and Baja California Sur. Notes: Anatomically and in pycnidial characters Placidium andicola is very similar to P. pilosellum that has somewhat larger spores and whose squamules tend to have free margins and usually pale lower surfaces. However, the discrimination may be difficult.