Bringing Back Wisconsin Native Thistles
Native thistles are a largely misunderstood and wrongly maligned group of wildflowers.
Often confused with their prickly, invasive relatives such as Canada thistle, in reality,
native thistles are benign and valuable plants that fill a variety of significant niches alongside
more esteemed wildflowers such as coneflowers, prairie clovers, and blazing star.
Native thistles fill important niches in our ecosystems. In great grasslands and prairies,
and silty Midwestern river bottoms, the seeds of our native thistles help sustain enormous flocks of
songbirds such as goldfinches and indigo buntings. The nectar of these plants fills the stomachs of
countless flower visitors while the foliage of thistles feeds both people and rare butterflies alike.
Swamp thistle (Cirsium muticum) is a caterpillar host plant for the Swamp Metalmark butterfly
(Calephelis muticum), listed as endangered in Wisconsin.
Native thistles fill important niches in our ecosystems. The nectar of these plants fills the
stomachs of countless flower visitors, including the enormous
Black and Gold Bumble Bee, while the foliage of thistles feeds butterflies.
Thistle seeds are a major food source for birds and other wildlife, as well as for a variety of invertebrates.
The abundant nectar and pollen found in thistle flowers make them one of the most popular plants among
both pollinator and non-pollinator invertebrates.
Sure, they’ve got spines, but so do cacti, yucca, and many other plants gardeners love to landscape with.
As if that wasn’t enough, most thistles have large and/or abundant blossoms, which you’d think would make
them very attractive to people.
Native thistles are a favorite of many of our native Bumble Bee species including:
Two-spotted,
Black and Gold,
Northern Amber,
Yellow,
Brown Belted and
Common Eastern Bumble Bees.
As with so many of our other native prairie and meadow species, thistles have been a direct casualty of
habitat loss due to agriculture, urbanization, and the development of cities and roads. Most significantly,
they have suffered from the invasion of non-native thistles as indiscriminate weed control efforts often
eradicate native thistles along with their problematic relatives. Many of our policies and activities are
heralding the potential end of these beautiful plants. A number of native thistle species are now threatened
with extinction.
Our contempt for thistles causes serious problems for pollinators.
Native thistles deserve to be returned to their rightful place in the landscape. Xerces’ new publication
Thistles: A Conservation Practitioner’s Guide provides the information necessary to do this. The
guide includes a comprehensive discussion of thistle taxonomy, highlights the value of native thistles for
pollinators and other wildlife, and provides a detailed account of the conservation status of native thistles.
Given the significance of the invasion of non-native thistles and the ramifications of the non-native species
on their native counterparts, Xerces provides a brief history of the arrival, spread, and efforts to control
one of the most invasive thistles in North America, Canada thistle. Finally, the guide provides a section on
the production of native thistle seed for use in restoration projects.
This section on propagation and seed
production is based on multiple years of actual native thistle seed production by the Xerces Society
Pollinator Conservation Program in partnership with a group of fantastic native seed companies.
Wisconsin Native Thistles
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Field Thistle
Benefits: Bees, Birds, Butterflies
Height: 6 feet
Bloom Time: Fall
Sun: Full Sun, Part Sun
Zones: 3-8
Soil: Loam
Moisture: Dry, Medium
Color: Purple
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Description: Field Thistle, Cirsium discolor, also called Pasture
Thistle is biennial or short-lived perennial plant initially forms a low rosette of spiny basal leaves up to 1
foot across. Flower heads with little or no scent occur individually on erect flowering stems in the upper
part of the plant. These flower heads are about 2" across and light pink (rarely white), consisting of
numerous disk florets.
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Flodman's Thistle
Benefits: Bees
Height: 1-2 feet
Bloom Time: Summer
Sun: Full Sun
Zones: 3-9
Soil : Loam
Moisture: Medium, Moist, Wet
Color: Purple
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Description: Flodman's Thistle, Cirsium flodmanii, is a
non-aggressive, native thistle. This showy thistle has beautiful magenta colored flower heads and is
favored by the American Goldfinch. This plant is an indicator of remnant prairie. Leaves are alternate and
deeply lobed, about 6 inches long. Flower heads are reddish purple to rose, 1 to 2 inches wide, single or a
few at the end of branching stems at the top of the plant.
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Swamp Thistle
Benefits: Bees, Birds
Height: 7 feet
Bloom Time: Late Summer/Early Fall
Sun: Full Sun, Part Sun
Zones: 2-9
Soil : Loam
Moisture: Moist, Wet
Color: Purple
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Description: Swamp Thistle, Cirsium muticum, is a native and
non-invasive thistle that produces vibrant purple to pink flowers and is weakly armed compared to other
thistles. It is biennial but will re-seed in appropriate habitat. It is best grown in full sun to moderate shade
on wet soils. The deep purple to pink flower heads rarely more than 1½ inches wide.
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Tall Thistle
Benefits: Bees, Birds, Butterflies
Height: 7 feet
Bloom Time: Late Summer, Early Fall
Sun: Full Sun, Part Sun
Zones: 3-9
Soil: Loam
Moisture: Medium
Color: Purple
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Description: Tall Thistle, Cirsium altissimum, is a native and
non-invasive thistle that is a biennial or short-lived perennial. The central stem and side stems are light
green to reddish brown, terete with several longitudinal ridges, and pubescent-woolly. The alternate
leaves are up to 9 inches long and 3 inches across. The upper stems terminate in individual flower heads
spanning about 2 inches across. Each flower head has a multitude of small disk florets that are pink to
purplish pink.
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