Scientific Name: Cirsium arvense

Common Name: Canada thistle

Other Common Names: california thistle, creeping thistle, field thistle

Synonyms: Breea arvensis, Breea incana, Carduus arvensis, Cirsium arvense var. argenteum, Cirsium arvense var. horridum, Cirsium arvense var. integrifolium, Cirsium arvense var. vestitum, Cirsium incanum, Cirsium setosum, Serratula arvensis

Habit: Canada Thistle produces flowers from about June until August. Generally, new shoots begin to form in January. The species spreads by creeping roots which in turn causes Canada thistle to often form dense patches.

Leaves: Leaves are generally oblong with edges that are lobed and spiny. Leaves are dark green and smooth on top portion and light green and often hairy on the lower portion. Leaves are attached to stems by way of a clasping base.

Identifying Characteristics: The plant reproduces by seeds and dense patches of shoots emerge from creeping roots.

Flower Seed Head: Small lavender flower heads consist of as many as 100 lavender tubular flowers. Flower heads are flask-shaped, 1/4 to 3/4 inch wide. The flower heads are produced singly or in groups of 2 to 5 at the ends of stems and axillary branches.

Seed Fruit: Mature seeds are brown, 3/16 inch long. A plume of tannish silky hairs is attached to one end.

Where Found: The Canada thistle plant grows in cultivated fields, pastures, rangelands, roadsides, waste places, and other open areas.

  • Life cycle: perennial

  • Milky sap: Not Present

  • Plant type: Herb

  • Thorns: Present

  • Plant family: Asteraceae

  • Leaf arrangement: alternate

  • Leaf shape: oval

  • Ochrea: Not Present

  • Leaf margin: lobed; serrated

  • Stem hairs: no hairs; has hairs

  • Flower color: purple; pink

  • Growth habit: upright and nonwoody

  • Stem: round or oval

  • Leaf structure: simple

  • Leaf hairs: has hairs; no hairs

  • Flower symmetry: radial symmetery

  • Flower diameter: dime; pencil; nickle

  • Root structure: rhizomes present; taproot

  • Leaf stalk: none