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Weed Identification

Virginia Tech College of Agriculture and Life Science Virginia Cooperative Extension

bull thistle

Family

Asteraceae

Scientific Name

Cirsium vulgare
Weed photograph 1
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Weed photograph 9
Weed photograph 10

Other Common Names:

common thistle
spear thistle
thistle

Synonyms (former Scientific Names):

Cirsium lanceolatum
Carduus vulgaris
Carduus lanceolatus

Habit

Bull thistle blooms from June to October. Bull thistle rosettes remain green and continue growing throughout the winter.

Leaves

The rosette leaves ranging between 3 to 7 inches long. The upper portion of the leaf is dark green and covered with sharp prickly hairs, while the lower portion of the leaf is a lighter green and is covered with soft hairs that have a wooly feel. The stem leaves are somewhat similar to rosette leaves just smaller in size. Leaves are attached to the stem and extend down it offering a winged looked. Leaves are indented around the edge with groups of 2 or 3 spine-tipped lobes interspersed with non-lobed portions.

Identifying Characteristics

Reproduction is performed only through the seeds. Bull thistle plants can produce approximately 7000 seeds.

Flower Seed Head

The flowers are located at the end of stems covered in spiny hairs. The outer rim of the flower is green and spiny itself, and contains many disk shaped flowers that are reddish-purple.

Seed Fruit

The seeds are straw colored with a black streak approximately 1/6 inch long. One end of the seed contains many brown hairs.

Where Found

The bull thistle is now established on every continent except the frozen tundra of Antarctica. It grows as a weed in pastures, roadsides, and fields that have been abandoned. It prefers disturbed areas with rich and moist soils.

Growth Habit

upright and nonwoody

Thorns or Spines

present

Approximate Flower Diameter

Varies: 
nickle, 
quarter, 
half dollar, 
larger

Dominant Flower Color

Varies: 
purple, 
red

Flower Symmetry

radial symmetery

Leaf Hairs

has hairs

Leaf Shape

oval

Leaf Arrangement

Varies: 
alternate, 
opposite, 
rosette

Leaf Margin

Varies: 
entire, 
lobed, 
serrated

Leaf Structure

simple

Leaf Stalk

none

Stem Hairs

has hairs

Stem Cross Section

round or oval

Milky Sap

not present

Root Structure

taproot

Life Cycle

biennial

Ochrea

not present

Plant Type

Herb