FEIS: DISTRIBUTION AND OCCURRENCE:
"Spotted knapweed is native to eastern Europe, though it now occurs in western and central Europe. It was introduced to North America, probably as a contaminant in alfalfa (Medicago sativa) seed and/or ship's ballast, in the late 1800s ... . In 1920, the distribution of spotted knapweed in North America was limited to the San Juan Islands, Washington."
Information on California plants for education, research and conservation,
with data contributed by
public and private institutions and individuals,
Consortium of California Herbaria.[web application]. 2020. Berkeley, California:The Calflora Database
[a non-profit organization].Available:
https://www.calflora.org/(Accessed: Oct 21, 2020).