Marsh Thistle

Cirsium palustre

Family: Asteraceae

Other Scientific Names:

Carduus chailleti, Carduus laciniatus, Carduus palustris, Cirsium chailletii, Cirsium kochianum, Cirsium laciniatum, Cirsium lacteum, Cirsium palatinum, Cirsium parviflorum, Cnicus palustris, Cynara palustris

Other Common Names: Swamp thistle, European marsh thistle, European swamp thistle
Weed class: A
Year Listed: 2025
Native to: Europe
Is this Weed Toxic?:

Not known to be

Why Is It a Noxious Weed?

Marsh thistle is quickly expanding in North America, and has a high potential to infest many parts of Washington State. There are several infestations in British Columbia, which are close to the Washington border.

Additionally, they can hybridize with creeping thistle (Cirsium arvense) and bull thistle (Cirsium vulgare).

How would I identify it?

General Description

Herbaceous biennial or monocarpic perennial thistle. This means it only blooms once, but may live for multiple years until it does so. For the first year, or until it blooms, it lives as a rosette of spiny leaves, before bolting into a tall flowering stalk.

Flower Description

Clusters of pink to pink-purple thistle heads at the top and tips of flowering stems. The petals are made of disk flowers, and look very frilly. Each flowering head has a bulb of green and green-purple bracts, which often have spines on the tips.

Leaf description

The hightly dissected and spiny leaves of the basal rosette can be up to 1 foot long. The leaves on the flowering stalk are similarly dissected and lobed, but grow smaller the higher on the stem they are. In the shade, leaves will be wider and less spines, than those growing in sun.

Stem description

Only grow stems when ready to flower and seed. The green to green-purple stems can be 2 to 7 feet tall. They usually have spined wings that go lengthwise along the stems.

Fruit Seed Description

Small, brown to black seeds attached to a feathery pappus (like a dandelion seed)

May Be Confused With

Several of our native and non native thistles look very similar to marsh thistle. Generally, marsh thistle's flowers are smaller than most noxious thistle species, with the exception of creeping thistle (Cirsium arvense). Marsh thistle grows much taller than creeping thistle, and has rosettes, while creeping thistle does not grow obvious rosettes. However, the two species can hybridize with characteristics overlapping between both parent species.

Where does it grow?

Moist, wet, and damp sites, in full shade to full sun, in both Eastern and Western Washington.

How Does it Reproduce?

Seed only, however when hybridized with creeping thistle (Cirsium arvense), it is likely to be able to reproduce by creeping underground rhyzomes.

How Do I Control It?

Pull or dig out the entire taproot of small infestations.

Mowing can suppress flowering if done before June. Cutting in August can prevent seed maturation. The success of these methods in controlling plants varies with site, stand age, and the weather that year.

There is not much information on chemical control for marsh thistle. Herbicides should be applied toe the leaves when the rosettes are small, or before they develop a flowering stalk. Always follow label directions, local rules and regulations, and wear appropriate personal protective equipment when applying herbicide.