Batty, Lesley C. e Hallberg, Kevin B. (a cura di), Ecology of Industrial Pollution, Ecological Reviews, Cambridge University Press, 2010, p. 49, ISBN 9780521514460. URL consultato il 4 dicembre 2012.
«Usnea spp., at one time widespread and luxuriant, almost entirely disappeared from a major area of England and Wales covering at least 68 000 km² and at least 6 000 km² of lowland Scotland, mainly as a result of the increase in atmospheric pollution.»