Origin: Introduced from the Great Plains of the central United States
Notes: No specimens from Washington are known. Considered excluded here until evidence suggests otherwise.
References:
» Tutin, T. G., V. H. Heywood, N. A. Burges, D. M. Moore, D. H. Valentine, S. M. Walters and D.A. Webb, eds. 1980. Flora Europaea, Vol. 5, Alismataceae to Orchidaceae (Monocotyledones). Cambridge Univ. Press, Cambridge, UK. 452 p.