Description: This native biennial or short-lived
perennial plant is 2-8' tall, forming occasional branches that remain erect.
The stems have white hairs, but
are without spines.
The alternate leaves are quite spiny, pinnately lobed, and up to 9" long and 3"
across. They are green on the upper surface, but powdery white on the lower
surface because of fine hairs. Flowerheads with little or no scent occur
individually on erect flowering stems in the upper part of the plant. These
flowerheads are about 2" across, and are light pink, light lavender, bright
pink, or white (rarely), consisting of numerous narrow tube-shaped flowers
about 1½" long. At the base of the individual flowers are overlapping
green bracts with white edges, resembling fish scales. These bracts often have
fine spines, which are otherwise absent. The blooming period is from late
summer to fall, and lasts about a month for individual plants. The achenes
develop with tufts of white hair, which facilitates their dispersion by wind.
The root system consists of a central taproot and some coarse secondary roots.
Vegetative spread by rhizomes does not occur.
Cultivation: The preference is full sun, loamy soil,
and average moisture levels, although other kinds of soil are tolerated,
particularly clay and gravel. During summer droughts, there is a tendency for
the lower leaves to turn yellow and fall off the plant. This is an easy plant
to grow, but it has a tendency to appear rather the worse for wear as the
growing season progresses. Pasture Thistle is short-lived, but reseeds itself
readily, forming a small rosette of leaves during the first year of
growth.
Range & Habitat: This
common plant occurs in virtually every county in Illinois (see
Distribution
Map). Habitats include moist to dry prairies, openings in woodland areas,
moist meadows near rivers, limestone glades, pastures and abandoned fields,
open areas along railroads and roadsides, and waste areas. This plant is more
abundant in disturbed areas, including degraded prairies, but also occurs in
higher quality habitats.
Faunal
Associations: The most important pollinators of the flowers are
bumblebees, Miner bees, other long-tongued bees, and butterflies. Among the
butterflies, are such visitors as Monarchs, Fritillaries, Painted Ladies,
Swallowtails, and Sulfurs. Sphinx moths and bee flies also visit the flowers
for nectar. The caterpillars of the butterfly Vanessa cardui (Painted
Lady) feed on the foliage, while the caterpillars of several moths feed on the
foliage and other parts of this and other thistles (see
Moth Table). The Eastern Goldfinch eats the
seeds and uses the tufts of hair as lining material in their nests. The
Ruby-Throated Hummingbird has been known to visit the flowers of thistles for
nectar. Mammalian herbivores don't feed on this plant because of the
spines.
Photographic Location: The
photographs were taken near Kaufman Lake Park in Champaign,
Illinois.
Comments: This native
plant can be distinguished from the non-native Cirsium vulgare (Bull
Thistle) by the white undersides of its leaves. Also, the green bracts
subtending the flowerheads of Bull Thistle have numerous coarse spines, whereas
the bracts of the Pasture Thistle have only a few fine spines, or none at all.
Otherwise, they are similar in appearance. Sometimes this plant can be
aggressive in disturbed areas, but not to the same extent as the Bull Thistle.
It is possible to boil the young leaves and stems and serve them as edible
greens. During the month of August, when other forbs are less likely to flower,
this plant produces some patches of pink color, making the prairie more
interesting during this time of year.