Invasive Plant Guide: Giant PlumelessThistle


Carduus acanthoidesNathan Donnelly pulls thistle

Identifying characteristics

  • Flower color: pink-purple
  • Flowers:July to September
  • Stems: partly winged; spiny.  Multiple flower-heads at end of stems.
  • Plant height: ranges from about 1 foot to 6 feet
  • Leaves: very spiny
  • Seeds:
  • Growth habit: annual/biennial


Open disturbed sites, roadsides, fields, pastures, hillsides, rangeland, forest openings. Prefers warm, dry climate areas.  Tolerates a wide range of soil types.

Giant plumeless thistle (Carduus acanthoides) is found in only one location in the mid-Klamath.  This is also the only known location in all of Siskiyou County.



Plant spreads by seed only. Seeds are viable for up to seven years, and germinate aggressively. 

More Info

California Invasive Plants Council
California Department of Food & Agriculture