Canada Thistle (Cirsium arvense)

Status:

Listed Noxious Weed In Montana & North Dakota

History:

First Montana Specimen Collected 1

County:

Musselshell

Year:

1881

“Canada thistle is a native or Eurasia and was probably introduced to America around 1750.  Canada thistle was first described in taxonomic texts in 1753 under the Latin name Serratula arvensis L.  The first state to enact noxious weed legislation against Canada thistle was Vermont in 1795 followed by New York in 1831 [147]”. (Wilson)The first recorded infestation in Montana was collected in Musselshell County in 1881.

Habitat:

“Canada thistle is adaptable to a wide range of habitats. It occurs in nearly every
upland herbaceous community within its range, particularly prairie
communities and riparian habitats [162]. It is most commonly found in
disturbed areas as part of the initial post disturbance community along
roadsides, railroads, stream banks, ditches, lakeshores, seashores, sand
dunes and other open sandy areas,[153] in clear cuts and forest
openings, and in wet and wet-mesic grasslands and prairie potholes.”(Zouhar)

Growth Habit:

Perennial, erect, up to 4 ft. tall.

Leaves:

Varies from light to dark green, oblong or lance shaped, deeply cut, spiny toothed margins
(some may be smooth slightly hairy below. Tremendous leaf variability.

Stem:

Smooth to slightly hairy, branched top.

Flower:

Small bristly clusters, 3/8 to 5/8 inch in diameter, light lavender to deep rose
purple Plants are male or female.

Roots:

Extensive, fleshy, creeping rootstocks.

Seeds:

Smooth, light to dark brown, tipped by a cupped conical point, approx. 1/8" long.

Other Notes:

Reproduces by seed and creeping rootstocks.