Onopordum acanthium

Onopordum acanthium_ Scotch thistle_JM DiTomaso_cropped
Photo: 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.

Cal-IPC Rating: High?

CDFA Rating: -*?


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.

Species ID Card

Invasive Species ID Card - To support field identification of early detection species, Cal-IPC has designed a set of Species ID cards that can be downloaded, printed double-sided, and trimmed to size.

Weed Management Notes

  • Management Notes - Information on management techniques and effectiveness from the University of California Cooperative Extension’s Weed Research & Information Center.

Cal-IPC Newsletter Articles

Cal-IPC Symposium Presentations

Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.

There are no Symposium presentations associated with this species yet.

Other Onopordum acanthium Information

  • CalPhotos - Images of plants taken mostly in California.
  • Calflora - Distribution map and records of this species in California.
  • CalWeedMapper - Distribution map of this species in California with ability to determine regional priorities.
  • EDDMapS - Distribution of this species in North America.
  • Jepson Interchange - Information on this plant's taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • USDA PLANTS Database - Information on identification and distribution, with links to websites in individual states.
  • Additional photos

    Onopordum acanthium_infestation_BobCase
    Onopordum acanthium (Scotch thistle) infestation. Photo: Bob Case
    Onopordum acanthium_stem (senescent)_ZoyaAkulova
    Onopordum acanthium (Scotch thistle) stem (senescent). Photo: Zoya Akulova
    Onopordum acanthium_seeds_ZoyaAkulova
    Onopordum acanthium (Scotch thistle) seeds. Photo: Zoya Akulova
    Onopordum acanthium_flower heads_RichardSpellenberg
    Onopordum acanthium (Scotch thistle) flower heads. Photo: Richard Spellenberg
    Onopordum acanthium_growth habit_Thayne Tuason
    Onopordum acanthium (Scotch thistle) growth habit. Photo: Thayne Tuason