Distribution: West of Cascades crest in Washington; northern British Columbia to lower California, disjuncts in Minnesota, Wisconsin, Maine, Vermont, New Hampshire, Virginia, North Carolina, South Carolina, Georgia.
Habitat: Open forest.
Substrate: On bark of all kinds, and occasionally on rock.
Conservation Status: Not of concern
Thallus pale grey, lobes somewhat divided, 6-15 mm in width. Abundant long cilia. Lower surface brown to black with wide naked margin.
PNW Herbaria: Specimen records of Parmotrema arnoldii in the Consortium of Pacific Northwest Herbaria database
CalPhotos: Parmotrema arnoldii photos