Canada thistle
Family
AsteraceaeScientific Name
Cirsium arvense
Other Common Names:
California thistle
creeping thistle
field thistle
Synonyms (former Scientific Names):
Cirsium setosum
Cirsium arvense var. integrifolium
Carduus arvensis
Cirsium arvense var. horridum
Breea incana
Cirsium arvense var. argenteum
Cirsium arvense var. vestitum
Serratula arvensis
Cirsium incanum
Breea 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.
Growth Habit
upright and nonwoody
Thorns or Spines
present
Approximate Flower Diameter
Varies:
pencil,
dime,
nickle
Dominant Flower Color
Varies:
purple,
pink
Flower Symmetry
radial symmetery
Leaf Hairs
Varies:
has hairs,
no hairs
Leaf Shape
oval
Leaf Arrangement
alternate
Leaf Margin
Varies:
lobed,
serrated
Leaf Structure
simple
Leaf Stalk
none
Stem Hairs
Varies:
has hairs,
no hairs
Stem Cross Section
round or oval
Milky Sap
not present
Root Structure
Varies:
taproot,
rhizomes present
Life Cycle
perennial
Ochrea
not present
Plant Type
Herb