Plumeless Thistle (Carduus acanthoides)

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Thistle can exceed two meters in height and can form weedy monotypic stands. The stem and foliage are spiny and sometimes woolly. The plant starts from a flat basal rosette and then bolts an erect stem with occasional toothed, wrinkled, spiny leaves. At the top of each branch of the stem is an inflorescence of one to several flower heads, each rounded, covered in spiny phyllaries, and bearing many threadlike purple disc florets.

Key Identifiers
  • Winged stem with many branches, candelabrum appearance
  • Wings are very spiny and continuous, not interrupted along the stem
  • Leaves deeply lobed and very pubescent
  • Yellow spines along a white-margined leaf margin
  • Short very sharp spines on bracts
  • Hairs along the mid-rib on underside of leaf
Location in Canada
C. acanthoides is found in British Columbia, Ontario, Quebec and Nova Scotia according to The Biology of Canadian Weeds. There is however a thriving population in Alberta along the Bow River. Carduus hybrids are also believed to be present in Alberta.

Todd Pfeiffer, Klamath County Weed Control,

Resources Similar species
Nodding thistles (Carduus nutans) has larger flowers (about 3 times the size of plumeless) and usually droop or nod at maturity. It is important to note Carduus thistles can hybridize, and both are very similar in the rosette stage. - Nodding Thistle

Bull thistle (Cirsium vulgare) is also a biennial with prickly, winged stems. The leaves are coarse and spiny above with wooly white hairs below. - Bull Thistle

Marsh Thistle (Cirsium palustre) a strongly spiny-winged thistle and are usually unbranched except the upper portion which terminates in clusters of purple flower heads - Marsh Thistle

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For more information about the content of this document, contact Chris Neeser.
This document is maintained by Shelley Barkley.
This information published to the web on April 10, 2012.
Last Reviewed/Revised on August 21, 2018.