Williams, Tara Y. (1990). "Cypripedium passerinum". Fire Effects Information System (FEIS). US Department of Agriculture (USDA), Forest Service (USFS), Rocky Mountain Research Station, Fire Sciences Laboratory. Archived from the original on 2011-02-25. Retrieved 2011-11-14.
Williams, Tara Y. (1990). "Cypripedium passerinum". Fire Effects Information System (FEIS). US Department of Agriculture (USDA), Forest Service (USFS), Rocky Mountain Research Station, Fire Sciences Laboratory. Archived from the original on 2011-02-25. Retrieved 2011-11-14.