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Horsetops Cirsium muticum

Other Common Name(s):

Phonetic Spelling
SIR-see-um mu-tee-kum
Description

Swamp Thistle is a native biennial plant in the Asteraceae (daisy) family that is native to central and eastern Canada and the United States. Its name comes from the Greek kersion which means thistle.  The specific epithet comes from the Latin word muticus, meaning blunt referring to its phyllaries.  The plant has tall branching stems that contain purple to pink flowers on spineless bracts. The plant often grows 2 to 5 feet tall (sometimes as high as 8 feet depending on the moisture level) with clasping leaves that are 10 inches long and 4 inches across. It is found in wet soil in meadows, prairies, marshes, swamps, bogs, and open woods.

Swamp thistle prefers full sun, wet to moist conditions and grows best in sandy soil although partial sun and other soil types are tolerated. It is propagated via seed, but expect it to take two years until it flowers. It forms a rosette of leaves the first year and sends up a flowering stem the second year with a solitary flower or a cluster of flowers. This thistle has fewer spines than some and is much easier to control than other thistles.

The thistle is a high-value nectar plant for bees and butterflies and the songbirds eat the seeds and use the tufts of the seeds for their nests. The seeds are rich in oil, an important food source for seed-eating birds. It is the host plant for the Swamp Metalmark butterfly (Calephelis muticum), and the Painted Lady Butterfly (Vanessa cardui) as well as moths, beetles, grasshoppers, and weevils. Flowers are also attractive to hummingbirds. Members of this genus support the following specialized bees: Thistle Long-horned bee Melissodes desponsus, plus Osmia (Helicosmia) chalybea and Osmia (Helicosmia) texana.

Swamp thistle is a great option in the wetlands of your meadow garden or naturalized area when looking for native host plants for the Swamp Metalmark butterfly or the Painted Lady butterfly. They are used to make decorative arrangements. If you want to plant a thistle in your gardens, this is the one to plant because they are easier to control than other thistles. They are non-invasive in North Carolina.

Quick ID Hints:

  • In a wetland habitat, the bracts are spineless and contain a mesh of cob-webby hairs.
  • White densely wooly underside of the leaves.

Insects, Diseases, and Other Plant Problems:  No significant problems.

 

See this plant in the following landscape:
Cultivars / Varieties:
Tags:
#full sun tolerant#biennial#moth caterpillar host#nectar plant#seedheads#wetlands#specialized bees#NC native#deer resistant#spines#native garden#prickly#wind dispersed seeds#pollinator plant#wildflower garden#larval host plant#wet soils tolerant#bird friendly#butterfly friendly#bee friendly#weed#moth friendly#wildlife friendly
 
Cultivars / Varieties:
Tags:
#full sun tolerant#biennial#moth caterpillar host#nectar plant#seedheads#wetlands#specialized bees#NC native#deer resistant#spines#native garden#prickly#wind dispersed seeds#pollinator plant#wildflower garden#larval host plant#wet soils tolerant#bird friendly#butterfly friendly#bee friendly#weed#moth friendly#wildlife friendly
  • Attributes:
    Genus:
    Cirsium
    Species:
    muticum
    Family:
    Asteraceae
    Life Cycle:
    Biennial
    Recommended Propagation Strategy:
    Seed
    Country Or Region Of Origin:
    Central and eastern Canada and United States
    Distribution:
    Prairies of southeastern Saskatchewan across southern Canada to Newfoundland and south in the United States from North Dakota and Maine to southeastern Texas and northern Florida.
    Wildlife Value:
    Members of the genus Cirsium support the following specialized bees: Melissodes (Heliomelissodes) desponsus, Osmia (Helicosmia) chalybea and Osmia (Helicosmia) texana. Birds eat the seeds.
    Particularly Resistant To (Insects/Diseases/Other Problems):
    Tolerant of wet soils and are not often visited by deer.
  • Whole Plant Traits:
    Plant Type:
    Native Plant
    Weed
    Wildflower
    Habit/Form:
    Erect
    Growth Rate:
    Medium
    Maintenance:
    Low
    Texture:
    Coarse
    Appendage:
    Prickles
    Spines
  • Cultural Conditions:
    Light:
    Full sun (6 or more hours of direct sunlight a day)
    Soil Texture:
    Sand
    Soil pH:
    Acid (<6.0)
    Alkaline (>8.0)
    Neutral (6.0-8.0)
    Soil Drainage:
    Moist
    Occasionally Wet
    Available Space To Plant:
    12 inches-3 feet
    NC Region:
    Coastal
    Mountains
    Piedmont
    USDA Plant Hardiness Zone:
    2a, 2b, 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
  • Fruit:
    Fruit Color:
    Cream/Tan
    Fruit Value To Gardener:
    Showy
    Display/Harvest Time:
    Fall
    Fruit Type:
    Achene
    Fruit Length:
    < 1 inch
    Fruit Width:
    < 1 inch
    Fruit Description:
    Seeds are produced singly in a flat, dark brown fruit about 1/10 of an inch long. Seeds produce a feathery pappus (similar to dandelion ‘seeds’) which help disperse the seeds.
  • Flowers:
    Flower Color:
    Pink
    Purple/Lavender
    Flower Inflorescence:
    Head
    Flower Value To Gardener:
    Good Cut
    Showy
    Flower Bloom Time:
    Fall
    Summer
    Flower Shape:
    Dome
    Flower Size:
    1-3 inches
    Flower Description:
    Purple to pink flower heads are a dense cluster of numerous disk florets up to 2.5 inches wide on a hollow flowering stem. The sticky bracts are not tipped with spines. Blooms late summer to fall.
  • Leaves:
    Leaf Color:
    Green
    Leaf Feel:
    Prickly
    Leaf Type:
    Simple
    Leaf Arrangement:
    Alternate
    Rosulate
    Leaf Shape:
    Elliptical
    Obovate
    Ovate
    Pinnatifid
    Leaf Margin:
    Lobed
    Hairs Present:
    Yes
    Leaf Length:
    > 6 inches
    Leaf Width:
    3-6 inches
    Leaf Description:
    Rosette of long-stalked, deeply incised leaves up to 16 inches long and 4 inches across growing alternately on the stem. They are pinnately cut into broad prickly segments with spiny tips. The leaves become gradually smaller in size as they grow up the stems. The top of the leaves are green but the underside is whitened from a dense coating of white hairs when the leaves are young. These hairs thin when older and the underside of the leaf becomes pale green.
  • Stem:
    Stem Color:
    Green
    Stem Is Aromatic:
    No
    Stem Cross Section:
    Round
    Stem Surface:
    Hairy (pubescent)
    Stem Description:
    Green finely grooved longitudinally.
  • Landscape:
    Landscape Location:
    Meadow
    Naturalized Area
    Landscape Theme:
    Pollinator Garden
    Attracts:
    Butterflies
    Moths
    Pollinators
    Songbirds
    Specialized Bees
    Problems:
    Spines/Thorns
    Weedy