Presented by The Friends of the Wildflower Garden
Thistles Comparison
Wild Thistles found in Minnesota
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WILD THISTLE COMPARISON: There are seven recognized thistles found in Minnesota. Three are non-native and one is not common. Eloise Butler included 4 of these thistles on her list of indigenous plants of the Eloise Butler Wildflower Garden. Of those 4 only Field and Swamp Thistle are still present, but Canada Thistle arrived. She listed C. undulatum, as one of the 4. That species is currently named Wavy-leaved thistle and is not currently known to be in Minnesota. However, the U of M Herbarium states that it is easily confused with C. flodmanii, Flodman's Thistle, which is common in 2/3rds of the state. Also, the C. pumilum, Pasture Thistle, in Minnesota is now classed as var. hillii. (Hill's Thistle).
Below the descriptive keys are photos of the flower head and leaf, the two most easily distinguished characteristics. Several have links to a more complete photo and info sheet.
| Name | Canada Thistle | Field Thistle | Swamp Thistle | Pasture Thistle (Hill's Thistle) | Flodman's Thistle | Bull Thistle | Tall Thistle |
| Species | C. arvense | C. discolor | C. muticum | C. pumilum var. hillii | C. flodmanii | C. vulgare | C. altissimum |
| E.B. List | No | Yes | Yes | Yes | Yes | No | No |
| Height | 1 to 4' | 2 to 7' | 2 to 7' | 1 to 3' | 1 to 3-1/2' | 2 to 6" | 3 to 10' |
| Longevity | Perennial | Biennial | Biennial | Biennial to perennial | Perennial | Biennial | Biennial |
| Stems | Erect, ridged, little hair, occasional branching near top. No wings. | Erect, white hair overall, branching in upper half. No wings. | Erect. Some hair on lower section otherwise smooth, no wings, much branched. | Erect, few, if any, branches, spiny, no wings | Stout, erect, dense white fuzz, usually un branched. no wings. | Erect, dense white hair, small wings descending from leaf to leaf with spines. | Erect, widely branched and hairy, ridged, no wings. Tallest of the thistles. |
| Leaves | Lanceolate, deep indents but not to rib; base touches stem or clasps, spines on margins pointing in many directions, upper surface smooth, lower whitish with fine hair | Lanceolate, deeply divided to rib, spiny, upper surface smooth, lower whitish with fine hair | Lanceolate to oblong, deeply divided, soft spines, if any, on tips of lobes, green topside, light green under with fine whitish hair which depletes with age. Basal leaves of rosette very large, to 16" long. | Lance-like, lobes shallow, not cut to central rib, covered with rough hair and spines on the lobes, green on underside, leaves well spaced; basal leaves persistent. | Lanceolate, pinnately-divided, but not down to the central rib; coarse teeth, triangular lobes with spines on the tips; dark green above and whitish fuzz on underside | Lanceolate, lobed with spines on lobes, small teeth on lobes, upper surface with rough short hair, underside light green with woolly hair. | Lanceolate, shallow lobes,if any, not cut deeply, spiny teeth on margin, smooth on top, underside with dense white hair. Stalkless or very short stalks. |
| Flower | Pinkish, 1/2" wide; phyllaries short, green to purple, tightly appressed with slightly spreading sharp pointed purple tips. Fragrant | Pinkish, to 1-1/2" wide; phyllaries dark green with white vertical stripe and each with slender spine, resemble fish scales, ascending leaf bracts looking like small leaves at base of head. Not fragrant | Purple to pink, to 1-1/2" wide; phyllaries elongated, deep green, light color vertical stripe, with white-woolly webbing, not spiny. Sticky from resin. Ascending leafy bracts looking like small leaves | Pink to purple, to 1-3" wide, on a stalk well above leaves; phyllaries elongated triangles, dark green to purplish, with light green vertical central rib, with sharp purple tips that curl outward. Flower fragrant | Purple to rose, - 1 to 2" wide, rounded base; phyllaries elongated, medium green with long white center vertical stripe and with a short sharp spine. | Purple, to 1-1/2" wide; phyllaries green with sharp tips that curl outward. Cobwebby hair among phyllaries. At least 1 leafy bract below. | Pink to purple, to 1-1/4" wide; phyllaries dark green with lighter green vertical stripe and each with a slender spine, but shorter than Field Thistle. Resemble fish scales. Leafy ascending bracts at base of flower head. Some cobwebby hairs among the phyllaries. |
| Flower Position | Single & small clusters branching from upper stem | Single on erect stems branching from upper stem | Cluster of 2 to 5 heads | Solitary usually, or one per stem if branched. | Single or loose cluster of heads | Single or small open cluster, branching from upper stem | Single or many heads on a leafy stalk. |
| Bloom time | Early to mid summer | Late Summer | Late summer to fall | Early to late summer | Early to Late summer | Early to late summer | Late Summer to fall |
| Seed | Dry achene, brownish white pappus | Dry achene, whitish pappus | Dry achene with feathery pappus | Dry achene with feathery pappus | Dry achene with feathery pappus, slimy when wet | Dry achene with long white pappus | Dry achene with feathery pappus |
| Habitat | Sun, wide range of moist soils. Forms clumps | Sun, loamy soils, medium moisture, open fields | Wet places | Sunny prairie and sandy soil | Moist poorly drained areas | Full sun, variety of soils, disturbed sites | Sun, dry to moderate soil conditions, loamy soil, waste places. |
| Minnesota Native Status | Non-native, invasive | Native | Native | Native, Special concern list | Native | Non-native, invasive if allowed to reseed | Native |
| Distribution in Minnesota | Common | Common | Common | Not common | Common in 2/3rds of state | Common | Found in 1/3rd of state |
C. arvense
C. discolor
C. muticum
C. altissimum
(Hill's Thistle)
C. pumilum var. hillii
C. flodmanii
C. vulgare