BULL THISTLE (Cirsium vulgare)

How to Identify Bull Thistle (Cirsium vulgare)
This is Bull Thistle, a member of the family Asteraceae that is native to Eurasia, and has become a noxious weed in The United States and in Australia. It is a biennial that flowers from mid to late summer.

The plant is composed of many spreading branches that reach 2 to 5 feet tall. The stems are green or brownish, and are covered in stiff, coarse hairs.

The leaves are long, thin, and very deeply lobed, and have an array of sharp, thin prickles along their margin and at the tips of each lobe. The. Leaves are hairy on their upper surface, and cottony or woolly on their lower surfaces. They are green with a distinct grayish hue, and the midrib and spines are colored yellow. The bases of the leaves extend down the stem and form irregular spiny wings.

Plants in their first year of growth appear dramatically different, forming small, tight rosettes. The leaves are only lightly toothed, and are much woolier, giving them a soft appearance. They are slightly ruffled along their margin, and are a light green color.

The flowers may be clustered in small groups at the tops of the stems, and are surrounded by large, spiny bracts. The flowers are pink to purple in color, and when pollinated will produce a head of white parachuted seeds.

The plant grows off a short, fleshy taproot, and only reproduces via seed.

Bull thistle likes full sun and disturbed soil, and can tolerate a variety of moisture levels. They are common in pastures, fields, roadsides, gardens, and any other disturbed sites.

The stems and roots of this plant are edible.

Bull thistle can be confused with many other thistle species, but can be distinguished mainly by the shape and texture of the leaves, and the form of the flower bracts.

Musk thistle is a species that is often confused with bull thistle, but its leaves are lighter green in color, have a cream-colored margin, and are not nearly as deeply lobed. The flowers are slightly larger, fuller, and don’t have the dramatically spiny bracts found on bull thistle’s flowers.

Canada thistle, or creeping thistle, is another species that is often confused with bull thistle, but it has much darker colored leaves that are smooth on their upper surface, and only slightly hairy beneath. The flowering heads are easily distinguished from bull thistle, as they are much smaller and more densely clustered at the tops of the stems.

Despite its highly competitive, invasive tendencies, Bull thistle is not always considered a detrimental addition to the environment, as it serves as a valuable food and nectar source for many different birds and insects.


Sources:

Weeds of the West, 5th Edition (1991) by Tom D. Whitson, published by the Western Society of Weed Science

University of California Agriculture and Natural Resources IPM – Weed Gallery
http://ipm.ucanr.edu/

United States Department of Agriculture – Plant Database
https://plants.usda.gov