Abstract:
Squarrose knapweed, introduced from southwest Asia and the Middle East, became weedy in northern California and Utah by the early 1950s. How it
was originally introduced is not known, but its spread in California
and Utah was associated with the trailing of range sheep. Squarrose knapweed grows in the Klamath, Cascade, and northern Sierra Nevada Ranges and the Modoc Plateau in California. It has been documented in Humboldt, Siskiyou, Trinity, Shasta, Modoc, Lassen, and Plumas counties. In Utah, it grows on 150,000 acres in Juab, Tooele, Millard, Utah, and Sanpete counties, down from nearly 200,000 acres in the early 1990s.
