Centaurea jacea, Brown Knapweed

Gardens & Landscapes, Invasive Species, Extension Master Gardener December 15, 2015 Print Friendly and PDF

Invasive Species: Centaurea jacea, Brown Knapweed

Brown knapweed is an invasive perennial plant that grows 1 to 3 ft (0.3 to 0.9 m) tall and invades dry fields, roadsides, and meadows. The basal leaves are oblanceolate to elliptic and 2 to 10 in. (5 to 25 cm) long. Leaves become smaller and more linear as they move up the stem. Flowering occurs from June to September, when magenta flowers appear in 1 to 1¼ in. (2.5 to 3.2 cm) wide, solitary heads at the tips of the branches. Brown knapweed produces small, light brown, plumeless seeds, about 12 per head. Brown knapweed is native to Europe.

What are invasive species and why should we be concerned about them? 


Taxonomy: Scientific and Common Names for This Species

Asterales > Asteraceae > Centaurea jacea L.

Synonym(s): brown knapweed

Centaurea jacea - USDA PLANTS Profile

Distribution Maps

Brown 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

Brown knapweed is an invasive perennial plant that grows 1 to 3 ft (0.3 to 0.9 m) tall.

brown knapweed brown knapweed
Cindy Roche, bugwood.org Bruce Ackley, Ohio State University, bugwood.org

Foliage

The basal leaves are oblanceolate to elliptic and 2 to 10 in. (5 to 25 cm) long. Leaves become smaller and more linear as they move up the stem.

brown knapweed brown knapweed
Bruce Ackley, Ohio State University,   ugwood.org Bruce Ackley, Ohio State University,   bugwood.org

Flower

Flowering occurs from June to September, when magenta flowers appear in 1 to 1¼ in. (2.5 to 3.2 cm) wide, solitary heads at the tips of the branches.

brown knapweed brown knapweed
Cindy Roche,  bugwood.org Bruce Ackley, Ohio State University,   bugwood.org

Fruit

Brown knapweed produces small, light brown, plumeless seeds, about 12 per head.

brown knapweed brown knapweed
Bruce Ackley, Ohio State University,   bugwood.org Bruce Ackley, Ohio State University,   bugwood.org

Native Centaurea Species That Resemble Brown 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

tall ironweed tall ironweed

Bruce Ackley, The Ohio State University,
bugwood.org

Bruce Ackley, The Ohio State University,
bugwood.org

 

Additional Images for Brown Knapweed

Brown knapweed - Images at Invasive.org

 

Learning Resources for Brown Knapweed

Centaurea jacea Identification Card - US Fish & Wildlife Service

Centaurea jacea Fact Sheet - US Fish & Wildlife Service

 

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.

Weed of the Week - USDA Forest Service

Centaurea jacea - Flora of North America

Connecticut Wildflowers - Connecticut Botanical Society

Centaurea jacea - BUGWOOD Wiki

Invasive.org - Center for Invasive Species and Ecosystem Health

Jepson Herbarium - University of California


 

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