Publication: Rhodora. 48: 124. 1946.
selected vouchers: WTU
Notes: Vestigial hybrids with P. sagittatus are found in Kittitas Co. (Bogle 1961, 1968).
» Bogle, A. L. 1961. A study of the genus Petasites in the Pacific Northwest, with special reference to Petasites warrenii St. John. Unpublished M.S. thesis, University of Washington, Seattle.
» Bogle, A. L. 1968. Evidence for the hybrid origin of Petasites warrenii and P. vitifolius. Rhodora 70: 533-551.