: Marsh thistle
: Best surveyed in summer and fall. In combination, it's small flowers/seed heads and spiny stems distinguish it from other thistles.
: Herbaceous biennial ranging from 0.5-1.5 m (1.6-5 ft) in height.
: Alternate, deeply divided into pinnate segments with matted hairs and spiny teeth along margins; blades narrowly elliptic to oblanceolate; narrow lobes separated by broad sinuses.
: Spiny with lengthwise wings; single; erect; villous to tomentose with jointed trichomes; distally tomentose with fine, unbranched trichomes; branches 0-few; sometimes reddish in color; branching at the top.
: Densely clustered purple flower heads are 1-1.5 cm (0.4-0.6 in) across, smaller than those of other thistle species, spiny and composed of disk flowers.
Fruit and seeds
: Fruits are achenes, small, 3 mm long, attached to a pappus or thistledown.
: Native to Eurasia. Found in moist soils; occurs in fens, forested or partially forested wetlands, disturbed sites including roadsides and ditches.
: Wind-dispersed seeds, which may also be transported on animals.
: The native Marsh Thistle (Cirsium muticum
) has non-spiny stems and flower heads. Other common invasive thistles include Canada thistle (Cirsium arvense
) which has spiny leaves but non-spiny stems and flower heads. Bull thistle (Cirsium vulgare
) and Plumeless thistle (Carduus acanthoides
which have sharply spined leaves, stems and flower heads.
Monitoring and rapid response
: Monitor moist acidic sites including wetlands, forest edges and fields; European swamp thistle blooms in June and July but can be identified by its thorny winged stems and small flower heads throughout the growing season. Mowing or cutting close to the ground throughout the growing season can reduce infestations; flower heads should be removed from site. Foliar herbicide treatment effective; can be used on fall rosettes, when plants are small, 10-25 cm (6-10 in) and during the bud/flowering stage.
: The Michigan Natural Features Inventory
(MNFI) has partnered with MISIN to provide the information in this fact sheet. Species images and/or information were used with permission from "A Field Identification Guide to Invasive Plants in Michigan's Natural Communities
" and "A Field Guide to Invasive Plants of Aquatic and Wetland Habitats for Michigan