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Wisconsin Plant of the Week

Carduus nutans L.

Asteraceae (Sunflower Family)

Common Name:

nodding thistle, musk thistle

07/03/2000

Nodding thistle was introduced to Wisconsin in the early 1900’s. It’s become an aggressive invader in old fields, disturbed pastures and roadsides and a common pest in grassland restorations. It’s a biennial with a long taproot and spreads easily by seed.

Leaves of the first year basal rosette can be up to 50 cm long.  They’re smooth on both sides, with a light midvein and a stout white spine at the tip of each lobe. Leaves on the second year flowering stem are similar, but smaller and arranged alternately.  The base of each leaf forms a spiny wing along the otherwise smooth stem.

The flowering stem is up to 2 m tall.  Showy rose-purple flowers are in a solitary head up to 8 cm across and 3 cm high that droops when mature. Bracts under the flowers are purple, smooth, wide, tapered to a stout spine and bent backward or reflexed.  The stem between the flower head and the first leaf is smooth and covered with a cottony web. Flowers bloom in June and July.

Like all the thistles this one has hair-like structures, or “pappus”, attached to each seed, which allows the wind to carry the seeds for long distances.  Grassland birds also use the pappus for nesting material.

Most of our other thistles are in the genus Cirsium. These are distinguished by bracts under the flowers that are bent upward and leaves whose surface is rough or covered with hairs or prickles.  The pappus in the Cirsium is branched like a feather or plume, rather than the simple straight hairs in Carduus.

Not all thistles are weedy.  Several are native and noninvasive and so one needs positive identification before beginning a control program.

See WDNR’s Invasive Species Fact Sheet for thistle control methods.

  • Origin of the name: Carduus, L., a thistle; nutans, L., drooping or nodding
  • Range:  s. Europe, w. Asia, N. Africa,  introduced throughout N. America
  • WI Range:  Mostly in the south, occasionally northward
  • Common associates: Ragweed, sweet clover, mullein
  • Wetland Indicator Status: UPL
  • Coefficient of Conservatism: C = * (S&W), C = * (MI)
     
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