World distribution: The species occurs in South, Central, and North America, western Europe and in the central European mountains (Hale 1965, Purvis & James 1992c). In northwest Europe the species shows a western British Isles to western Norway disjunct distribution. In Fennoscandia the species is known only from Norway
Ecology: Results. The species grows on north-facing, acid, moss covered boulders and rock walls in open Betula forest. Discussion. In the British Isles the species grows among mosses, especially on horizontal branches of trees and old shrubs in more or less well-lit woodlands (Purvis & James 1992c)
Threats: Results. The species is threatened by planting of Picea and subsequent closure of the forest stand
Status: The locality was investigated in 1993. The population consists of two separate subpopulations, comprising a total of about 50 thalli/colonies. The site is not protected
Notes: The report of corticolous specimens by Havaas (1910) and Degelius (1935) may owe their origins to confusion P. arnoldii and P. chinense (cf. Hasselrot 1942). The geographical data on the labels of the two collections by Havaas differ somewhat, but we are not convinced they actually represent two different localities..
Specimens in other herbaria, litterature, etc.