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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.

Musk thistle plant with pink, purple and brown flowers

How to identify musk thistle

  • 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 leaves
Musk thistle
Musk thistle flower with pink and white bracts
Musk thistle

 

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

Reviewed in 2019

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