thistle was introduced into the United States from Europe. This
plant is considered a noxious weed and is included on the Colorado
and the Adams County Noxious Weed Lists. Musk thistle is a biennial,
which means its first year of growth is a rosette from a stout,
corky taproot. Rosettes can appear in either spring or fall. During
the second year, the stem bolts and can grow 2 to 6 feet tall. Musk
thistle has waxy, spiny leaves. These spines can cause physical
harm to wildlife and humans. Leaves are 3 to 6 inches long and are
dark green in color with a prominent midrib.
thistle produces many flowers; one plant may produce 100 or more
flowerheads. The nodding flowers are large, 1-1/2 to 2-1/2 inches
wide, purple, and surrounded by numerous lance-shaped, spine-tipped
bracts. Flowering occurs between late May and early June and set
seed in late June/early July.
thistle is usually found as a single plant rather than in dense
colonies like Canada thistle and leafy spurge. Musk thistle is found
in many county locations such as rangeland, riparian areas, and
ditch bank sites. If you think you have this weed on your property,
or would like more information, please contact the Adams County
Weed Department at 303-637-8115.