[Imbricaria revoluta (Flörke) Flot., more, Imbricaria sinuosa f. concentrica Arnold, Parmelia forsteri Leight., Parmelia laevigata var. forsteri (Leight.) Leight., Parmelia quercina var. erratica (Linds.) Hillmann, Parmelia revoluta Flörke, Parmelia revoluta f. foliolifera Erichsen, Parmelia revoluta f. isidiosa Müll. Arg., Parmelia revoluta f. nuda Müll. Arg., Parmelia revoluta f. revoluta Flörke, Parmelia revoluta var. britannica (D. Hawksw. & P. James) V. Wirth, Parmelia revoluta var. concentrica (Arnold) Cromb., Parmelia revoluta var. erratica (Linds.) Zahlbr., Parmelia revoluta var. granulata Harm., Parmelia revoluta var. minor Harm., Parmelia revoluta var. revoluta Flörke, Parmelia sinuosa var. erratica Linds., Parmelia sinuosa var. excentrica Mudd]
Thallus: foliose, 2-8 (-10) cm in diam., loosely adnate to adnate, irregularly lobate lobes: sublinear to subirregular, often short, plane to convex, usually separate, rarely slightly imbricate, 1-4 mm wide; axils: often sinuous; margin: entire, rarely somewhat incised; apices subtruncate to rounded, often revolute (especially when sorediate), convex to subascending, often black upper surface: gray to greenish gray, smooth, shiny, faintly white maculate or emaculate soredia: initially farinose, becoming granular, initially in subcapitate, subterminal soralia that become crateriform, excavated pustulae, with age becoming confluent and often eroded, white or greenish white; isidia and dactyls absent medulla: white or off-white with continuous algal layer lower surface: black, brownish towards apices; rhizines: sparse, black, sparsely dichotomous Apothecia: very rare, sessile to substipitate, 2-6 mm in diam.; disc: brown asci: clavate, 8-spored ascospores: ellipsoid to broadly ellipsoid, 10-12 x 6-8 µm Pycnidia: not seen Spot tests: upper cortex K+ yellow, C-, KC-, P+ yellow, UV-; medulla K-, C+ red, KC+ red, P- Secondary metabolites: upper cortex with atranorin and chloroatranorin; medulla with gyrophoric acids (major), 4, 5-di-O-methylhiascic acid, 5-O-methylhiascic acid (both minor), lecanoric and umbilicaric acids (both trace or absent). Substrate and ecology: relatively rare, on acidic rock or bark in lower montane and upper montane forests World distribution: neotropical and pantemperate (at least in regions adjacent to the tropics) Sonoran distribution: Channel Islands of California and montane areas of SE Arizona. Notes: This widespread species exhibits considerable morphological plasticity that requires further evaluation.