Cypripedium arietinum, the ram's head lady's slipper,[2] is a rare terrestrial orchid that grows in lightly to heavily shaded areas with calcareous soils. It is characteristic of the alvars around the Great Lakes in North America].[2][3] In Canada, it is found from Quebec to Saskatchewan, plus an isolated population in Nova Scotia, where it grows on gypsum based soils, 330 km away from the nearest population in Maine.[4][5]
^Ames, D., P. B. Acheson, L. Heshka, B. Joyce, J. Neufeld, R. Reeves, E. Reimer, and I. Ward. 2005. Orchids of Manitoba: A field guide. Native Orchid Conservation Inc., Winnipeg.
^ abUSDA, NRCS (n.d.). "Cypripedium arietinum". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 1 July 2016.
^Catling, P.M.; Brownell, V.R. (1999). "Alvars of the Great Lakes Region". In Anderson, R. C.; Fralish, J. S.; Baskin, J. M. (eds.). Savannas, Barrens and Rock Outcrop Communities of North America. Cambridge: Cambridge University Press. pp. 375–391. ISBN9780511574627.
^Blaney, S.; Mazerolle, D. (2007). Nova Scotia Provincial Status Report on Ram's-Head Lady Slipper (Cypripredium arietinum R. Br.). Nova Scotia Department of Natural Resources.
^"Cypripedium arietinum". County-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). 2014.