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. Scotch 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 up to 8 feet tall.
This plant has large, hairy, spiny leaves which have a velvety-grey
thistle produces many flowers which are violet to reddish in color
and have spine-tipped bracts. Flowering occurs between mid-June
and early July. Flower heads remain upright, rather than nodding
as musk thistle flowers do.
thistle can create an impenetrable barrier to man and to wildlife
and nearly eliminates forage use by livestock and big game species
such as deer and elk.
thistle is found in many county locations such as rangeland, riparian
areas, and ditch bank sites.