Bringing Back Wisconsin Native Thistles

Bee pollinating a native thistle 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 are a valuable resource for public land managers, native seed producers, and landowners as they take steps to conserve and protect a beautiful and important group of native plants

Native thistles are a favorite of many of our native Bumble Bee species including: Two-spotted, Black and Gold, Northern Amber, Yellow Spotted, Brown Belted and Common Eastern Bumble Bees.

Native Thistles Are Disappearing

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.

Bringing Thistles Back

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.

4 Wisconsin Native Thistles

Field Thistle, Cirsium discolor Field Thistle
Benefits: Bees, Birds, Butterflies
Height: 6 feet
Bloom Time: Fall
Sun: Full Sun, Part Sun
Zones: 3, 4, 5
Soil: Loam
Moisture: Dry, Medium
Color: Purple
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.
Flodman's Thistle, Cirsium flodmanii Flodman's Thistle
Benefits: Bees
Height: 1-2 feet
Bloom Time: Summer
Sun: Full Sun
Zones: 2, 3, 4, 5
Soil : Loam
Moisture: Medium, Moist, Wet
Color: Purple
Description: Flodmans 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.
Swamp Thistle, Cirsium muticum Swamp Thistle
Benefits: Bees, Birds
Height: 7 feet
Bloom Time: Late Summer/Early Fall
Sun: Full Sun, Part Sun
Zones: 2, 3, 4, 5
Soil : Loam
Moisture: Moist, Wet
Color: Purple
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.
Tall Thistle, Cirsium altissimum Tall Thistle
Benefits: Bees, Birds, Butterflies
Height: 7 feet
Bloom Time: Late Summer, Early Fall
Sun: Full Sun, Part Sun
Zones: 3, 4, 5
Soil: Loam
Moisture: Medium
Color: Purple
Description: Tall Thistle, Cirsium altissimum, is a native and non-invasice 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.

Further Information:   

Wisconsin Bee Identification Guide
Spring Wild Bees of Wisconsin
Bumble Bees of Wisconsin
Wild Native Bee Nest Boxes