Large herbaceous biennial. When the plant bolts in the second year it can be three to six feet tall. Stems are freely branching and have leaf-like spines.
OverviewOther names for this plant
- Common names: spiny plumeless thistle, welted thistle
- Infest low-quality areas first, such as roadsides, disturbed areas, ditch banks and old fields. Spreads into high-quality prairies.
- When in meadows and pastures, grazing animals avoid plumeless thistle and focus on native plants giving the invasive the upper hand.
Classification in Wisconsin: Restricted
Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for plumeless thistle was based upon this literature review developed by the department.
First-year plants-leaves: First-year rosette leaves are up to two inches long, deeply divided with lobes ending with spines.
Second-year plants-Leaves: Dark green with light green midrib and hairy on the underside; leaves are deeply divided with lobes ending in a spine.
Flowers: Red-purple flowers singly or in clusters. Flower heads are up to one inch in diameter.
Fruits & seeds: Up to 10,000 seeds per plant with seeds disperse within seven to 10 days of flowering. Seeds are viable in the soil for more than 10 years.
Roots: Single taproot.
Similar species: Musk thistle (Carduus nutans) is very similar except for the solitary flower is much larger, 1 1/2 to three inches wide and slightly nodding. The leaves are also hairless on both sides.
Mechanical: Close mowing of second-year plants twice per growing season just before flowering. Cut or mow at early bud both times. Cut plants with a sharp shovel one to two inches below soil surface before flowering.
Chemical: Spot spray rosettes in fall with 2, 4-D ester; foliar spray with clopyralid or metsulfuron-methyl.
View plumeless thistle pictures in our photo gallery.