Onopordum acanthium

Photo courtesy Joseph DiTomaso

Common names: Scotch thistle; cotton thistle; woolly thistle; winged thistle; jackass thistle; heraldic thistle

Onopordum acanthium (Scotch thistle) is a biennial or short-lived perennial (family Asteraceae) which is primarily found in the northeastern regions of California. Severe infestations can form tall, dense, impenetrable stands, especially in fertile soils. Onopordum acanthium reproduces only by seeds, which can germinate year round, and it is drought resistant. Infestations can reduce forage and impede movement for livestock and wildlife.

Rating: High

Cal-IPC Resources

  • Plant Assessment Form - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.
  • CalWeedMapper - Statewide maps, climate models, and reports.
  • Cal-IPC News - Our quarterly newsletter. Each issue is available as a pdf.
  • Cal-IPC Symposium Proceedings - Presentations and papers from our annual Symposium.
  • Don't Plant a Pest! - Select your region to find non-invasive alternatives to ornamental species. Also see our statewide brochure on trees.

    Other Resources

    Symposium Presentations

    • Leavitt, J. R. and C. Pirosko (2002). A brief overview of the California Dept. of Food and Agriculture’s A-rated noxious weed education and eradication program. California Exotic Pest Plant Council Symposium 2002. Sacramento, CA.
    • O'Connell, R. A. (1999). The state of California's noxious weed eradication programs. California Exotic Pest Plant Council. Sacramento, CA.
    • Carrithers, V. F. (1997). Using Transline* herbicide to control invasive plants. California Exotic Pest Plant Council Symposium '97. Concord, CA.
    • O'Connell, R. A. (1997). Hydrilla: A case study: The state of California's noxious weed eradication programs. California Exotic Pest Plant Council Symposium '97. Concord, CA.

    Cal-IPC News Articles

    • Brusati, E., D. Morawitz, et al. (2011). Prioritizing Regional Response to Invasive Plants in the Sierra Nevada. Cal-IPC News. 19: 4, 5, 10.
    • Richardson, B. (2004). The A-rated north. Cal-IPC News. 12: 4-5,14.
    • Donaldson, S. (2003). Fighting weeds in the Tahoe basin. CalEPPC News. 11: 7.
    • Pitcairn, M. (2000). All weeds that have approved biological control agents, accidental introductions and others. CalEPPC News. 8.