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Brown Knapweed

Centaurea jacea

Please keep in mind that it is illegal to uproot a plant without the landowner's consent and care should be taken at all times not to damage wild plants. Wild plants should never be picked for pleasure and some plants are protected by law.
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Plant Profile

Flowering Months:
Asteraceae (Daisy)
Also in this family:
Alpine Blue Sow-thistle, Alpine Cotula, Alpine Fleabane, Alpine Saw-wort, Annual Ragweed, Annual Sunflower, Argentine Fleabane, Autumn Hawkbit, Autumn Oxeye, Beaked Hawksbeard, Beggarticks, Bilbao Fleabane, Black Knapweed, Black-eyed Susan, Blanketflower, Blue Fleabane, Blue Globe-thistle, Bristly Oxtongue, Broad-leaved Cudweed, Broad-leaved Ragwort, Butterbur, Buttonweed, Cabbage Thistle, Canadian Fleabane, Canadian Goldenrod, Carline Thistle, Chalk Knapweed, Chamois Ragwort, Changing Michaelmas Daisy, Chicory, Chinese Mugwort, Chinese Ragwort, Coltsfoot, Common Blue Sow-thistle, Common Cat's-ear, Common Cudweed, Common Daisy, Common Dandelion, Common Fleabane, Common Goldenrod, Common Groundsel, Common Michaelmas Daisy, Common Mugwort, Common Ragwort, Common Wormwood, Coneflower, Confused Michaelmas Daisy, Corn Chamomile, Corn Marigold, Cornflower, Cotton Thistle, Cottonweed, Creeping Thistle, Daisy Bush, Dwarf Cudweed, Dwarf Thistle, Early Goldenrod, Eastern Groundsel, Eastern Leopardsbane, Elecampane, English Hawkweed, Fen Ragwort, Feverfew, Field Fleawort, Field Wormwood, Fox and Cubs, French Tarragon, Gallant Soldier, Garden Lettuce, Giant Butterbur, Glabrous-headed Hawkweed, Glandular Globe-thistle, Glaucous Michaelmas Daisy, Globe Artichoke, Globe-thistle, Goat's Beard, Golden Ragwort, Golden Samphire, Goldilocks Aster, Grass-leaved Goldenrod, Great Lettuce, Greater Burdock, Greater Knapweed, Grey-headed Hawkweed, Guernsey Fleabane, Hairless Blue Sow-thistle, Hairless Leptinella, Hairy Michaelmas Daisy, Harpur Crewe's Leopardsbane, Hawkweed Oxtongue, Heath Cudweed, Heath Groundsel, Hemp Agrimony, Highland Cudweed, Hoary Mugwort, Hoary Ragwort, Hybrid Knapweed, Intermediate Burdock, Irish Fleabane, Jersey Cudweed, Jerusalem Artichoke, Lance-leaved Hawkweed, Lavender-cotton, Leafless Hawksbeard, Least Lettuce, Leopardplant, Leopardsbane, Leptinella, Lesser Burdock, Lesser Hawkbit, Lesser Sunflower, London Bur-marigold, Magellan Ragwort, Marsh Cudweed, Marsh Hawksbeard, Marsh Ragwort, Marsh Sow-thistle, Marsh Thistle, Meadow Thistle, Melancholy Thistle, Mexican Fleabane, Milk Thistle, Mountain Everlasting, Mouse-ear Hawkweed, Musk Thistle, Narrow-leaved Cudweed, Narrow-leaved Hawkweed, Narrow-leaved Michaelmas Daisy, Narrow-leaved Ragwort, New England Hawkweed, New Zealand Holly, Nipplewort, Nodding Bur-marigold, Northern Hawksbeard, Norwegian Mugwort, Oxeye Daisy, Oxford Ragwort, Pearly Everlasting, Perennial Cornflower, Perennial Ragweed, Perennial Sow-thistle, Perennial Sunflower, Pineapple Mayweed, Plantain-leaved Leopardsbane, Ploughman's Spikenard, Plymouth Thistle, Pontic Blue Sow-thistle, Pot Marigold, Prickly Lettuce, Prickly Sow-thistle, Purple Coltsfoot, Rayed Tansy, Red Star Thistle, Red-seeded Dandelion, Red-tipped Cudweed, Robin's Plantain, Roman Chamomile, Rough Cocklebur, Rough Hawkbit, Rough Hawksbeard, Russian Lettuce, Safflower, Salsify, Saw-wort, Scented Mayweed, Scentless Mayweed, Sea Aster, Sea Mayweed, Sea Wormwood, Seaside Daisy, Shaggy Mouse-ear Hawkweed, Shaggy Soldier, Shasta Daisy, Shetland Mouse-ear Hawkweed, Shrub Ragwort, Sicilian Chamomile, Silver Ragwort, Slender Mugwort, Slender Thistle, Small Cudweed, Small Fleabane, Smooth Cat's-ear, Smooth Hawksbeard, Smooth Sow-thistle, Sneezeweed, Sneezewort, Spear Thistle, Spotted Cat's-ear, Spotted Hawkweed, Sticky Groundsel, Stinking Chamomile, Stinking Hawksbeard, Tall Fleabane, Tall Mouse-ear Hawkweed, Tansy, Thin-leaved Sunflower, Treasureflower, Trifid Bur-marigold, Tuberous Thistle, Tyneside Leopardplant, Viper's Grass, Wall Lettuce, Welsh Groundsel, Welted Thistle, White African Daisy, White Butterbur, White Buttons, Willdenow's Leopardsbane, Winter Heliotrope, Wood Burdock, Wood Ragwort, Woody Fleabane, Woolly Thistle, Yarrow, Yellow Chamomile, Yellow Fox and Cubs, Yellow Oxeye, Yellow Star Thistle, Yellow Thistle, York Groundsel
Life Cycle:
Maximum Size:
120 centimetres tall
Gardens, hedgerows, meadows, roadsides, wasteland, woodland.

Purple, many petals
Pale purple flowers, up to 3cm across. Brown bracts. 5 stamens per flower. Pollinated by bees, flies, butterflies and moths.
An elliptical seed, sometimes tipped by a few bristles. The seeds ripen from August to October. About a dozen seeds are produced per flowerhead.
Oblong to lance-shaped basal leaves, up to 10 inches (25cm) long. The leaves reduce in size as you move up the stem. Stem leaves are stalked and alternate. Basal leaves are stalkless. Very shallowly toothed or not toothed at all. Perennial.
Other Names:
Brownray Knapweed, Brown-rayed Knapweed, Common Knapweed, Hardheads.
Frequency (UK):
Rarely seen  

Similar Species

Other Information


Centaurea jacea, commonly known as brown knapweed, is a species of flowering plant in the aster family. It is native to Europe and Asia, but it has naturalized in many parts of the world, including North America. It is a perennial plant that produces large, showy, pink or purple flowers on tall, stiff stems. The leaves are deeply lobed, and the plant forms clumps of foliage. It is often used in landscaping and gardening, it prefers full sun and well-drained soil to grow well. It can be found in a variety of habitats such as meadows, pastures, roadsides, and waste areas. It is drought tolerant and can be grown in poor soil. It is often used in wildflower meadows, mixed borders, and cottage gardens. However, Brown knapweed can be invasive and crowd out native plants, so it's important to keep an eye on it and control it if necessary.


Brown Knapweed, also known as Centaurea jacea, is a perennial plant species that belongs to the Asteraceae family. It is native to Europe and western Asia but has been introduced to North America, where it is considered an invasive species. Brown Knapweed is commonly found in grasslands, meadows, and disturbed habitats such as roadsides, railroads, and waste areas. It is a competitive species that can rapidly spread and dominate an area, outcompeting native vegetation.

Identification and Characteristics

Brown Knapweed grows up to 3 feet tall and has a branched stem covered in hairs. The leaves are dark green, alternate, and deeply lobed, giving them a fern-like appearance. The flowers are small and clustered in dense, round heads at the end of the branches. The heads are surrounded by bracts with blackish tips, which give the plant its characteristic brown color. The flowers are pink to purple, and they bloom from June to September.

Ecological Impacts

Brown Knapweed is an aggressive invasive species that can cause significant ecological impacts. It outcompetes native vegetation, reducing biodiversity and altering plant community composition. Brown Knapweed is also unpalatable to many herbivores, which can lead to a decrease in wildlife habitat and biodiversity.

Brown Knapweed also has a negative impact on soil quality. It produces allelopathic chemicals that inhibit the growth of other plants, and it can also alter the soil nutrient balance. This can lead to a decline in soil fertility and productivity.

Control and Management

Due to its aggressive nature and negative impacts on ecosystems, Brown Knapweed is considered a noxious weed in many areas. Control and management strategies for Brown Knapweed typically involve a combination of chemical, mechanical, and cultural methods.

Chemical control involves the use of herbicides, which are most effective when applied during the plant's flowering stage. However, this method can have negative impacts on non-target species, and it should be used with caution.

Mechanical control involves manually removing the plant or cutting it down. This method is most effective when done before the plant flowers, as it can prevent seed production and spread.

Cultural control involves promoting healthy native vegetation through practices such as reseeding, mowing, and grazing. This can help to create a more competitive environment for Brown Knapweed, which can reduce its growth and spread.

More Information

In addition to its negative ecological impacts, Brown Knapweed also has economic impacts. It can reduce the productivity of agricultural lands and decrease the value of grazing lands. The presence of Brown Knapweed can also increase the cost of weed management for landowners and managers.

One of the reasons why Brown Knapweed is so successful as an invasive species is because it has a high reproductive capacity. It produces a large number of seeds that can be spread by wind, water, animals, and human activities. Once established, Brown Knapweed can form dense stands that can persist for many years.

Another challenge in controlling Brown Knapweed is that it can hybridize with other Centaurea species, which can create new invasive hybrids with unique characteristics. This highlights the importance of early detection and rapid response to new invasive species, as well as ongoing monitoring and management of established populations.

There are also biological control methods for managing Brown Knapweed, which involve introducing natural enemies of the plant to reduce its population. In North America, several biological control agents have been introduced, including a root-mining weevil (Cyphocleonus achates), a seed head weevil (Larinus minutus), and a seed-feeding fly (Urophora jacea). These natural enemies can help to reduce the seed production and spread of Brown Knapweed, but they are not always effective in controlling the plant.

It is important to note that while biological control methods can be effective, they should be used with caution to avoid unintended impacts on non-target species. Before introducing a biological control agent, thorough testing and monitoring should be done to assess its potential impacts on the environment.

In addition to the control and management of Brown Knapweed, there are also efforts to prevent the introduction and spread of invasive species. This includes regulations and policies that restrict the importation and movement of potentially invasive species, as well as public education and outreach to raise awareness about the impacts of invasive species and how to prevent their spread.

Research has shown that certain management strategies can be more effective than others depending on the characteristics of the invaded ecosystem and the biology of the invasive species. For example, some studies have found that mechanical control methods such as mowing and hand-pulling are more effective in controlling Brown Knapweed in grassland ecosystems than in forested areas.

Another approach to managing Brown Knapweed and other invasive species is through the use of citizen science. Citizen science involves engaging the public in data collection and monitoring efforts, which can help to increase the scale and effectiveness of invasive species management programs. Citizen science projects have been used to monitor Brown Knapweed populations and track the effectiveness of management strategies in various locations.

In addition to the ecological and economic impacts of invasive species, there are also social and cultural impacts to consider. Invasive species can disrupt traditional land management practices, reduce access to natural resources, and affect cultural practices and values. Recognizing and addressing these social and cultural impacts is an important aspect of effective invasive species management.

In conclusion, Brown Knapweed is a highly invasive species that poses significant ecological, economic, social, and cultural challenges. Effective management and control strategies require a comprehensive, collaborative, and adaptive approach that takes into account the characteristics of the invaded ecosystem, the biology of the invasive species, and the social and cultural context of the affected communities. By working together to manage and prevent the spread of invasive species, we can help to protect and preserve the health, biodiversity, and resilience of our ecosystems.