Thallus: foliose to subfruticose, up to c. 3 cm across [up to 8-15 cm elsewhere], thin (< 1 mm thick), papery lobes: few to numerous, upcurved, up to 2-5 (-20) mm wide; margins "ragged" [elsewhere sometimes branched and divided into fruticose lobes] upper surface: whitish, whitish green, pale blue-greenish gray, to pale greenish tan (turning green to olive or greenish gray or tan when wet), or occasionally tinged with yellow or reddish, often with darkened areas, shiny to matt, smooth or becoming incompletely and inconspicuously wrinkled to strongly reticulately wrinkled, without distinct pseudocyphellae but ± maculate in places soredia: initially white and granular, sometimes becoming brown and isidioid (simple to coralloid), often in laminal, rounded to irregular soralia or marginal, crescent-shaped soralia upper cortex: c. 15-25 µm thick medulla: white, c. 60-200 µm thick, I+ lavender lower cortex: 16-25 µm thick; rhizines: absent to few ( to many), brown or black, simple or branched lower surface: jet black towards center, or irregularly mottled or spotted brown or white towards the margins; shiny, smooth or reticulately wrinkled and coarsely and sometimes foveolate Apothecia: very rare, 0.5-1 cm broad, marginal, perforate or not; without algae below; hymenium: 34-56 µm; "subhymenium" 16-52 µm, I+ lavender to bright purple asci: clavate, I+ blue or blue-green, 8-spored ascospores: hyaline, simple, ellipsoid to ovoid, 3.5-8.5 x 3-5 µm Pycnidia: not seen Spot tests: cortex K+ yellow, C-, KC-, P+ yellow; medulla K-, C-, KC-, P-, UV- Secondary metabolites: cortex with atranorin and chloroatranorin; medulla with caperatic acid. Substrate and ecology: on trees (usually conifers) or shrubs, or wood, occasionally on rocks and rarely soil; in open woods World distribution: circumpolar and circumboreal in the Northern Hemisphere, Macaronesia; southern South America and E Africa Sonoran distribution: southern California, coastal mountains in chaparral and on Pseudotsuga macrocarpa. Notes: It is characterized by its loosely attached, suberect, greenish gray, smooth to ± wrinkled thallus with broad, dissected, rounded lobes with marginal soredia (often mixed with isidia) and a mottled brown and white lower surface, nearly without rhizines. It is extremely variable over its full range. Some forms might be confused with Esslingeriana idahoensis [non-Sonoran; with a black lower side and often black rimmed upper side], Cetrelia species, which have more distinct pseudocyphellae on the upper surface, or Parmotrema species, which usually have marginal cilia and a different chemistry. The two specimens seen from the Sonoran region are rather small and poorly developed.