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Plumeless thistle

Quick facts

Plumeless thistle is an invasive species. Plumeless thistle is on the Control noxious weed list meaning you must prevent the spread of this plant.

  • Plumeless thistle is most commonly found on highly disturbed sites and pastures.
  • It replaces native species quickly.
  • Plumeless thistle reduces desirable forage species.

Plumeless thistle should be reported. The Minnesota Department of Natural Resources provides detailed recommendations for reporting invasive species.

How to identify plumeless thistle

  • Plumeless thistle (Carduus acanthoides) is a biennial herbaceous plant that grows up to six feet tall.
  • Often has a basal rosette for the first year and bolts the second.

Stem

  • Branched stems have vertical leafy wings with spines on the tips and are covered with many spiny leaves.
  • Plant produces one to several flowering stocks when it bolts.
  • Flower stems are branched with spiny wings extending to the flower heads.

Leaves

  • Rosettes are four to eighteen inches wide, with deeply lobed, woolly, spiny leaves.
  • Bolted plant leaves are wavy, spiny, with hairy underside; long near the base and diminish in length as they ascend the plant.
  • Leaves are narrower and wavier than musk thistle.
  • The spiny leaves extend onto and around the stem, giving it the appearance of clusters of leafy spines throughout the plant.

Flowers

  • Small (one inch diameter), purple-pink singular or clustered flower heads contain many tiny individual flowers; can be bulbous shaped.
  • Blooms May to August.

Seeds

  • Small, oblong, slightly curved seeds, about 0.12 inches long are contained inside a thin-walled fruit.
  • They are loosely attached with tuft of hair.

Roots

  • Taproot
Plumeless thistle leaves
Plumeless thistle flower

 

 

Angela Gupta, Extension educator; Amy Rager, Extension educator; Megan M. Weber, Extension educator

Reviewed in 2019

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