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Hybrid Knapweed

Centaurea x gerstlaueria

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, Brown Knapweed, 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, 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, Trifid Bur-marigold, Tuberous Thistle, Tyneside Leopardplant, Viper's Grass, Wall Lettuce, Welsh Groundsel, Welted Thistle, 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:
1 metre tall
Fields, gardens, grassland, meadows, roadsides, scrub, wasteland, woodland.

Purple, many petals
Purple brush-like flowers with brown bracts, measuring up to 4cm across.
A seed (achene) with a tuft of bristly hairs at one end (the pappus). In fruit from August to October.
A branched perennial plant with untoothed, lance-shaped leaves. The leaves are alternate along the stems. Hybrid Knapweed is a hybrid between Black Knapweed (Centaurea nigra) and Brown Knapweed (Centaurea jacea).
Other Names:
Centaurea, Gerstlauer's Knapweed.
Frequency (UK):

Similar Species

Other Information


Centaurea x gerstlaueria, commonly known as Gerstlauer's knapweed or Centaurea, is a hybrid plant of the Centaurea genus. It is a cross between Centaurea montana and Centaurea jacea. Gerstlauer's knapweed is a perennial flowering plant that produces large, showy, pink or purple flowers. 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 is drought tolerant and can be grown in poor soil. It is often used in wildflower meadows, mixed borders, and cottage gardens. This plant is a hardy plant and it can tolerate a wide range of growing conditions.


Hybrid Knapweed, also known as Centaurea x gerstlaueria, is a plant species that is native to Europe and Asia, but has also been introduced to North America. It is a hybrid of two different knapweed species, the Spotted Knapweed (Centaurea stoebe) and the Brown Knapweed (Centaurea jacea). The hybridization between these two species has resulted in a plant that is more invasive and aggressive than either of its parent species.

Appearance and Characteristics

Hybrid Knapweed is a herbaceous perennial plant that can grow up to three feet tall. It has a deep taproot and a branched stem with numerous lateral branches. The leaves are lance-shaped and covered with fine hairs, giving them a grayish-green appearance. The flowers are pink or purple in color and have a cone-shaped center that is surrounded by spiky bracts. The plant blooms from June to September and produces large amounts of seeds that can remain viable in the soil for up to five years.

Invasive Species

Hybrid Knapweed is considered an invasive species in North America, where it has been introduced. It is particularly problematic in the western United States, where it has invaded rangelands, pastures, and disturbed areas. The plant is able to outcompete native vegetation, reduce biodiversity, and decrease forage availability for livestock and wildlife. Additionally, the plant has a negative impact on the soil, altering its chemistry and reducing its fertility.

Control and Management

Due to its aggressive nature, control and management of Hybrid Knapweed can be difficult. The plant has a deep taproot that makes mechanical removal challenging, as any small fragment of the root left behind can regrow into a new plant. Chemical control methods, such as herbicides, are often used to manage large infestations of the plant. However, care must be taken to avoid damaging non-target species and to ensure that the herbicide is applied correctly and safely.

In addition to chemical control, biological control methods have also been employed to manage Hybrid Knapweed. Several species of insects, such as the Knapweed Root Weevil and the Knapweed Gall Fly, have been introduced as biological control agents in North America. These insects feed on the plant's roots and stems, reducing its ability to grow and reproduce.

More Information

In addition to its negative impact on the environment and agriculture, Hybrid Knapweed can also have economic consequences. The plant can reduce the value of rangeland and pasture, as it decreases the availability of forage for livestock. It can also increase management costs for landowners, as control and management efforts can be time-consuming and expensive.

Prevention is the best strategy for managing Hybrid Knapweed. Measures such as monitoring and early detection of new infestations, implementing quarantine measures, and preventing the introduction and spread of the plant through equipment and vehicles can be effective in preventing the establishment of new populations.

It is also important to raise public awareness about the negative impacts of invasive species and encourage the use of native plant species in landscaping and restoration efforts. Education and outreach programs can help promote responsible land management practices and prevent the unintentional spread of invasive species.

Hybrid Knapweed is not only invasive in North America but also in other parts of the world, such as Australia, New Zealand, and South Africa. It is listed as a noxious weed in several states in the US and is regulated under various laws and regulations, including the Federal Noxious Weed Act.

Efforts to control and manage Hybrid Knapweed have been ongoing for several decades, and research into new control methods and technologies continues. Some recent studies have explored the potential of using fungal pathogens and biochar as alternative control methods. Biochar is a form of charcoal that is produced by heating organic materials in the absence of oxygen. It has been shown to have potential as a soil amendment that can suppress weed growth, including Hybrid Knapweed.

While effective control and management of Hybrid Knapweed can be challenging, it is important to continue efforts to prevent the spread of the plant and mitigate its impact on native ecosystems and agriculture. This requires a collaborative and integrated approach that involves government agencies, landowners, researchers, and the public. By working together, we can reduce the spread and impact of invasive species like Hybrid Knapweed and preserve the health and productivity of our natural resources.

In addition to the ecological and economic impacts of Hybrid Knapweed, there are also potential health risks associated with the plant. The spiky bracts that surround the flowers can cause skin irritation and are a potential hazard for animals that graze on the plant. The plant may also be toxic to some livestock species, such as horses and cattle, and can cause neurological symptoms and even death in severe cases.

To reduce the risk of skin irritation or other health issues, it is recommended to wear gloves and protective clothing when handling the plant. Livestock producers should be aware of the potential toxicity of the plant and take steps to prevent their animals from grazing on infested areas.

As with any invasive species, prevention is the best strategy for minimizing the impact of Hybrid Knapweed. This includes taking steps to prevent the introduction and spread of the plant, such as cleaning equipment and vehicles before moving them between locations, using certified weed-free forage and hay, and avoiding the purchase and planting of potentially invasive plant species.

In conclusion, Hybrid Knapweed is a highly invasive plant species that poses a significant threat to native ecosystems, agriculture, and potentially human and animal health. Effective control and management strategies, including prevention, chemical and biological control methods, public education and outreach, and research into new control methods, are essential to reduce the spread and impact of the plant and preserve the health and productivity of our natural resources.