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Musk thistle

Quick facts

Musk thistle is an invasive species.

  • Musk thistle colonizes in disturbed areas, such as pastures, roadside ditches, ditch banks, hayfields and disturbed prairies.
  • Seeds detach quickly and don’t fall far from parent plant, creating monoculture carpet.
  • Livestock do not eat it, giving it a competitive edge against native species.

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

How to identify musk thistle

  • Musk thistle (Carduus nutans) is a biennial herbaceous plant, between one to seven feet tall.
  • Musk thistle (also known as nodding thistle) overwinters in the rosette stage, four to eighteen inches wide. 
  • Second year plants usually bolt in late May.
  • Musk and plumeless thistles hybridize and are very similar in the rosette stage.

Stem

  • One to many branched stems covered with spiny wings.
  • Bolts in late May.

Leaves

  • Alternate, lanceolate, coarsely lobed and prickly; dark green with light-green/silver midrib and edges; and a smooth, waxy surface.
  • Prominent spines at the tip of each lobe clasps stem.
  • Basal leaves are four to sixteen inches long; leaf size reduces as they ascend the plant.

Flowers 

  • One to three inches wide; disk-shaped flower heads with large bracts contain hundreds of tiny individual purple flowers. 

  • Flower heads droop to a 90-degree angle from the stem when mature.
  • Blooms spring to early fall.

Seeds

  • Numerous straw-colored seeds with plume-like bristles inside a thin-walled fruit.
  • They survive in the soil for over ten years.
  • A single plant can produce around 20,000 seeds.

Roots

  • Each plant has a fibrous taproot.
Musk thistle
Musk thistle

 

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

Reviewed in 2019

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