Canada Thistle - Cirsium arvense

Family: Aster [E-flora]

[IFBC-E-flora]

[E-flora]

Habitat / Range
Mesic to dry roadsides, fields and disturbed areas in the lowland, steppe and montane zones; common in W, SC and NE BC; introduced from Eurasia. [IFBC-E-flora]
[IFBC-E-flora]

Origin Status: Exotic. [E-flora]


Identification


Additional Notes

Canada thistle is our only species of thistle with separate male and female plants (Moore 1979). Moore (1979) indicates that it was introduced to North America "very early in the colonial period, probably in the 17th century". A single seedling can produce a large patch through vegetative propagation (Moore 1979). This species is listed as one of the top fourteen species of concern by the Coastal Invasive Plant Committee, for more information visit their web site.


Similar Species

There are several plant genera commonly named “thistles”, and the reason for this is they look very similar and bear prickles. The most common ones are the Cirsium and Carduus genera. When trying to identify a Canada thistle-like plant with prickles, one should first check if it is really a Cirsium, or not. The easiest way is to see if the pappus bristles have conspicuous feather-like hairs, which makes them species in the genus Cirsium, or if the bristles are missing or very tiny, which is a feature of the genus Carduus. Following that, the Canada thistle can be readily separated from the other species of Cirsium based on the small involucres that are less than 2 cm in height. However, there is another small-headed thistle, similarly introduced from Europe, that could cause confusion--the marsh thistle (Cirsium palustre). However, this species does not have creeping rhizomes, and mostly grows in moist meadows.[1][E-flora]

From a distance, one might mistake knapweed species (Acroptilon or Centaurea) for the Canada thistle because of their pink flower heads and branching stems. However, their flowers are of varying sizes--those at the edge of the disk are larger than those near the center--and their leaves do not develop prickles. [1][E-flora]


Similar Species

There are several plant genera commonly named “thistles”, and the reason for this is they look very similar and bear prickles. The most common ones are the Cirsium and Carduus genera. When trying to identify a Canada thistle-like plant with prickles, one should first check if it is really a Cirsium, or not. The easiest way is to see if the pappus bristles have conspicuous feather-like hairs, which makes them species in the genus Cirsium, or if the bristles are missing or very tiny, which is a feature of the genus Carduus. Following that, the Canada thistle can be readily separated from the other species of Cirsium based on the small involucres that are less than 2 cm in height. However, there is another small-headed thistle, similarly introduced from Europe, that could cause confusion--the marsh thistle (Cirsium palustre). However, this species does not have creeping rhizomes, and mostly grows in moist meadows.

From a distance, one might mistake knapweed species (Acroptilon or Centaurea) for the Canada thistle because of their pink flower heads and branching stems. However, their flowers are of varying sizes--those at the edge of the disk are larger than those near the center--and their leaves do not develop prickles.

Note Author: Anna-Mária Csergo, February 2011.[E-flora]


Edible Uses

Other Uses

Medicinal Uses

Root: tonic, diuretic, astringent, antiphlogistic and hepatic[207]. [PFAF]

Plant: Contains a volatile alkaloid and a glycoside called cnicin, which has emetic and emmenagogue properties[240]. [PFAF]

Leaves: The leaves are antiphlogistic[207]. They cause inflammation and have irritating properties[207]. [PFAF]

Cultivation & Propagation


Synonyms

References