Carduus pycnocephalus

Carduus pycnocephalus_Italian thistle_JM DiTomaso
Photo: Joseph DiTomaso

Common names: Italian thistle

Carduus pycnocephalus (Italian thistle) is a winter annual forb (family Asteraceae) that is native to the Mediterranean region of southern Europe, northern Africa, western Asia. It is widely distributed in disturbed open sites, roadsides, pastures, annual grasslands, and waste areas across much of California. Plants grow up to 20 dm, are often slightly woolly, and narrowly winged along stems and spined. Flower heads typically occur in clusters of 2-5. Phyllary (flower head scale) margins are not scarious, unlike its close relative, C. tenuiflorus. Italian thistle can facilitate fire spread and frequency by providing fuels in some habitats and creates monocultures that reduce native seedling recruitment and survival. It is a host species for the introduced weevil, Rhinocilus conicus, which also attacks native thistles.

Cal-IPC Rating: Moderate?

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.

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.

Other Carduus pycnocephalus Information

  • Bugwood - National database from the Center for Invasive Species and Ecosystem Health at the University of Georgia.
  • 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.
  • GBIF - Global distribution information.
  • 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

    Carduus pycnocephalus_seedlings_copyright_2019_NealKramer
    Carduus pycnocephalus (Italian thistle) seedlings. Photo: © 2019 Neal Kramer
    Carduus pycnocephalus_flower heads (senescent)_ZoyaAkulova
    Carduus pycnocephalus (Italian thistle) flower heads (senescent). Photo: Zoya Akulova
    Carduus pycnocephalus_seed and pappus_ZoyaAkulova
    Carduus pycnocephalus (Italian thistle) seed and pappus. Photo: Zoya Akulova
    Carduus pycnocephalus_flower heads_BobCase
    Carduus pycnocephalus (Italian thistle) flower heads. Photo: Bob Case
    Carduus pycnocephalus_stem_KeirMorse
    Carduus pycnocephalus (Italian thistle) stem. Photo: Keir Morse
    Carduus pycnocephalus_phyllaries_copyright2001_FredHrusa(CDFA)
    Carduus pycnocephalus (Italian thistle) phyllaries. Photo: © 2001 Fred Hrusa, CDFA