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NOXIOUS WEED
CO, NM, UT

Cirsium arvense

Cirsium arvense. Synonym: Breea arvensis.  (Canada Thistle)
Asteraceae (Sunflower Family)

Foothills, montane. Meadows, disturbed areas.  Summer.
Near Yellow Jacket Canyon, August 3, 2005.

Over 200 years ago, Frederick Pursh said of Cirsium arvense in his Flora Americae Septentrionalis, "It is one of the most troublesome weeds, and when once introduced on a plantation it is almost impossible to get rid of it".

Cirsium arvense spreads easily (far too easily!) by both seed and root and it is, therefore, very difficult to exterminate.  Cutting down this Thistle only brings up five times as many root sprouts as before.  Using herbicides or cutting off the above ground stem every few days are two methods used for for decades to remove this noxious weed -- and these two methods don't work very well either. Biological controls have been used on several continents, but, in the words of one evaluation of these, "We conclude that the potential of pathogens for biocontrol of Cirsium arvense has largely been overestimated".

Leaves of Cirsium arvense are very prickly; flower heads are attractive, numerous, and very pleasantly sweet smelling; and seed production is enormous.  Flowers are unisexual and usually only male or female flowers occur on each plant.

In 1753 Linnaeus named this species, a native of Eurasia, "Serratula arvensis", it was renamed "Cirsium arvense" (its most widely accepted name today) in 1772.  Breea arvensis, the name which William Weber accepts, was given in 1832.

"Arvense" is Latin for "of fields", and "Breea" honors William Thomas Bree, botanist and theologian(More biographical information about Bree.)

Cirsium arvense

Cirsium arvense

Cirsium arvense. Synonym: Breea arvensis.  (Canada Thistle)
Asteraceae (Sunflower Family)

Foothills, montane. Meadows, disturbed areas.  Summer.
Near Yellow Jacket Canyon, August 26, 2005 and October 8, 2010.

The leaves of Cirsium arvense are narrow, deeply notched, and armed with numerous spiny tips.  It is common for basal rosettes of leaves to occur in clusters.

Cirsium arvense

Cirsium arvense

Cirsium arvense. Synonym: Breea arvensis.  (Canada Thistle)
Asteraceae (Sunflower Family)

Foothills, montane. Meadows, disturbed areas.  Summer.
Near Yellow Jacket Canyon, August 3, 2005.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Range map for Cirsium arvense