Centaurea nigra, Black Knapweed

Gardens & Landscapes, Invasive Species, Extension Master Gardener December 16, 2015 Print Friendly and PDF

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.

black knapweed  
Cindy Roche, bugwood.org

 

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.

black knapweed black knapweed
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.

black knapweed black knapweed
Cindy Roche,   bugwood.org Joseph M. DiTomaso, University of Californis-Davis, bugwood.org

Fruit

 

brown knapweed black knapweed
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

American star-thistle (Centaurea americana) American star-thistle (Centaurea americana)
Karan A. Rawlins, University of Georgia,  bugwood.org Karan A. Rawlins, University of Georgia,  bugwood.org

 

Vernonia gigantea, tall ironweed - Images at invasive.org

giant ironweed (Vernonia gigantea ssp. gigantea) tall ironweed
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


 

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.