Cirsium arvense (Canada Thistle)

Plant Info
Also known as: Field Thistle
Genus:Cirsium
Family:Asteraceae (Aster)
Life cycle:perennial
Origin:Europe
Status:
  • Invasive - ERADICATE!
  • Noxious Weed
  • Prohibited or Restricted species
Habitat:sun; old fields, along roads, waste areas, wetlands, lakeshores
Bloom season:June - October
Plant height:3 to 5 feet
Wetland Indicator Status:GP: FACU MW: FACU NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: indistinct Cluster type: panicle

[photo of flowers] Flower heads are ¾ inch across, lavender to pale pink or sometimes white. The bracts are flat, except for the tip which peels back away from the flower head. The bract tips are pointed but not spined, and typically a purplish color, sometimes the entire bract is tinged purple. One plant typically has numerous flower heads, single or in small clusters at the ends of branching stems.

Leaves and stem: Leaf attachment: alternate Leaf type: lobed Leaf type: simple

[photo of leaves] Leaves are stalkless, up to 6 inches long with yellow spines scattered along the wavy edges. The lower leaves are up to 2½ inches across and deeply lobed, with a spine at the tip of each lobe. The upper leaves are more narrow, and generally more toothed than lobed. Leaves may be somewhat hairy on the underside. The stem is light green, slightly ridged and may have scattered hairs but is not usually spiny.

Fruit: Fruit type: seed with plume

[photo of fruit] Fruit is a brown seed with a tuft of long white hairs to carry it off in the wind, spreading itself far and wide.

Notes:

Canada Thistle is highly aggressive, can form large, dense colonies from its creeping roots, and crowds out native plants pretty much everywhere it grows. It is fairly easy to identify from the numerous small lavender to pinkish flower heads, and bracts that have no spines. While it prefers moist conditions it can sprout up and persist just about anywhere. It is currently designated as a Prohibited-Control noxious weed in Minnesota, but the MN Weed Advisory group is recommending a change to Restricted noxious weed, due to "lack of a viable statewide control method". Unfortunately, the lack of a statewide program applies to pretty much all invasive species in Minnesota at this time and they are in essence giving up the pretense they can do anything to stop its spread. We can only hope that will change someday.

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More photos

Photos by K. Chayka and Peter M. Dziuk taken at various locations across Minnesota.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Jody - Manitoba
on: 2010-03-20 18:50:26

Once again Canada gets the blame, first it's our weather and now the weeds. Actually, Canada thistle is not native to Canada at all, and actually came across to canada with the first Eurpean settlers. It is native to Europe and Africa, therefore an invasive species.

Posted by: K. Chayka
on: 2010-03-20 21:38:14

Don't get down about it... It's only called Canada thistle because it invaded Canada first!

Posted by: Amy - Villa Park, Roseville, Ramsey County
on: 2012-07-03 20:52:32

Spotted this today around the water in the park

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