Not enough sampling effort. Thomson, John W. American Arctic Lichens: Vol. 2. The Microlichens. University of Wisconsin Press, 1997; Brodo, Irwin M., Sylvia Duran Sharnoff, and Stephen Sharnoff. Lichens of north America. Yale University Press, 2001; Brodo, Irwin M. Keys to Lichens of North America. Yale University Press, 2016.