Invasive Species: Centaurea nigra, Black Knapweed
Black knapweed is an invasive perennial plant that can grow from 1 to 3 ft. (0.3 to 0.9 m) tall. Leaves, near the base, are petiolate, oblanceolate, shallowly dentate, and 2 to 10 in. (5 to 25 cm) long. As leaves move up the stem, they become smaller, sessile, linear, and entire. Flowering occurs from June to October, when purple (rarely white) flowers appear in heads at the tips of the branches. Bracts that subtend the flower head are dark brown to black with numerous wiry lobes along the margins. Black knapweed is native to Europe and was first found in the United States in 1895 in Pullman, Washington. Preferred habitat includes roadsides, waste places, fields, and clearings.
What are invasive species and why should we be concerned about them?
Taxonomy: Scientific and Common Names for This Species
Asterales > Asteraceae > Centaurea nigra L.
Synonym(s): black knapweed
Centaurea nigra – USDA PLANTS Profile
Distribution Maps
Black knapweed – The reported distribution of this invasive species across the United States. (Source: Invasive Plant Atlas of the United States)
Up-to-the-minute distribution maps and why they are important.
Reporting This Invasive Species
What is the best way and place to report the occurrence of an invasive species?
How to report an invasive species sighting to EDDMapS – Early Detection & Distribution Mapping System
EDDMapS – Report an invasive species to EDDMapS
Cooperative Extension Offices – Find your local Cooperative Extension office on this map provided by USDA
How to Identify
This invasive species can be identified by looking for the characteristics described in the paragraphs that follow.
Plant
Black knapweed is an invasive perennial plant that can grow from 1 to 3 ft. (0.3 to 0.9 m) tall.
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| Cindy Roche, bugwood.org |
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Foliage
Leaves, near the base, are petiolate, oblanceolate, shallowly dentate, and 2 to 10 in. (5 to 25 cm) long. As leaves move up the stem, they become smaller, sessile, linear, and entire.
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| Bruce Ackley, Ohio State University, bugwood.org | Bruce Ackley, Ohio State University, bugwood.org |
Flower
Flowering occurs from June to October, when purple (rarely white) flowers appear in heads at the tips of the branches. Bracts that subtend the flower head are dark brown to black with numerous wiry lobes along the margins.
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| Cindy Roche, bugwood.org | Joseph M. DiTomaso, University of Californis-Davis, bugwood.org |
Fruit
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| Bruce Ackley, Ohio State University, bugwood.org | Bruce Ackley, The Ohio State University,bugwood.org |
Native Centaurea Species That Resemble Black Knapweed
Centaurea americana, American star-thistle – Images at invasive.org
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| Karan A. Rawlins, University of Georgia, bugwood.org | Karan A. Rawlins, University of Georgia, bugwood.org |
Vernonia gigantea, tall ironweed – Images at invasive.org
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| Theodore Webster, USDA Agricultural Research Service, bugwood.org |
Bruce Ackley, The Ohio State University, bugwood.org |
Additional Images for Black Knapweed
Black knapweed – Images at Invasive.org
Learning Resources for Black Knapweed
Additional Information, Biology, Control and Management Resources
Control and management recommendations vary according to individual circumstances. Location, habitat, weather, and a variety of other conditions are factors that help determine the best treatment choice. To find the safest and most effective treatment for your situation, consult your state’s land-grant institution. If you will use chemicals as part of the control process, always refer to the product label.
United States Land-Grant University System – Find your land-grant university’s College of Agriculture, Cooperative Extension Service, or other related partner on this map provided by USDA.
Invasive.org – Center For Invasive Species and Ecosystem Health
Noxious Weeds – King County
Jepson Herbarium – University of California
Noxious Weed Control – ODA Plant Division