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Perennial Ragweed

Ambrosia psilostachya

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, 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 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:
2 metres tall
Fields, grassland, roadsides, sand dunes, seaside, wasteland, woodland.

Yellow, no petals
Perennial Ragweed produces inconspicuous greenish flowers arranged in a spike-like inflorescence. These flowers, which bloom from late summer to fall, are small and lack the showy petals typical of more ornamental plants. The inflorescence, characterized by its spiky appearance, contributes to the plant's unique and recognisable features. The reproductive strategy of Ambrosia psilostachya relies on wind pollination, with the small flowers allowing for efficient dispersal of pollen. Despite their modest appearance, these flowers play a crucial role in the plant's life cycle and contribute to its ecological impact in its native habitats.
Perennial Ragweed consists of small, dry, and inconspicuous seeds. Encased within a tiny, one-seeded fruit called an achene, these seeds are designed for efficient wind dispersal, aiding in the plant's reproductive strategy. The achenes are often light in weight and equipped with structures that facilitate their transport over distances, contributing to the widespread distribution of the plant in its native habitats. While the fruit may not possess striking visual characteristics, its adaptive features align with the plant's ecological success, allowing for effective seed dispersal and colonisation in a variety of environments, from prairies to open woodlands.
Perennial Ragweed are finely divided and exhibit a feathery appearance, characterised by their delicate, serrated edges. These greyish-green leaves are arranged alternately along the stems of the plant. The intricate leaf structure, reminiscent of ferns, contributes to the plant's distinct visual appeal. The foliage is adapted to capture sunlight efficiently, essential for the photosynthetic processes that sustain the plant. As a native species in the UK, the finely cut leaves of Ambrosia psilostachya play a vital role in its overall aesthetic charm and ecological functionality within various habitats, such as prairies and open woodlands.
Perennial Ragweed is not generally associated with a distinctive or pleasant aroma. In fact, this plant is more renowned for causing hay fever allergies due to its potent pollen rather than for any fragrant qualities. The leaves and other vegetative parts of the plant do not emit a characteristic scent that would be noteworthy. Instead, its significance lies in its ecological role, invasive tendencies, and allergenic potential rather than any aromatic appeal.
Other Names:
Cuman Ragweed, Western Ragweed.
Frequency (UK):
Rarely seen  

Similar Species

Other Information


Ambrosia psilostachya, also known as Western Ragweed, is a species of flowering plant in the sunflower family (Asteraceae). It is native to North America and typically grows in dry to moderately moist areas, such as prairies, fields, and disturbed areas. The plant has small green or yellow flowers, which are not showy and are wind-pollinated. The leaves are deeply lobed and have a rough texture. It is considered a weed in many areas and can cause allergies in sensitive individuals, due to the release of pollen during late summer and fall.


Perennial ragweed, also known as Ambrosia psilostachya, is a plant species that is native to North America. It belongs to the Asteraceae family and is closely related to other species of ragweed, such as common ragweed (Ambrosia artemisiifolia) and western ragweed (Ambrosia tomentosa). Perennial ragweed is a common sight in many parts of North America, and it is known for its invasive nature and its ability to cause allergies in humans.

Physical Characteristics of Perennial Ragweed

Perennial ragweed is a herbaceous plant that typically grows to a height of 3-6 feet. The leaves of the plant are alternate, lanceolate, and deeply divided into three lobes. They are green in color and have a slightly hairy texture. The stem of the plant is also slightly hairy and can be green or reddish in color.

The flowers of the plant are small and inconspicuous, and they are arranged in long, cylindrical spikes at the top of the plant. The spikes are usually 4-8 inches long and contain both male and female flowers. The male flowers are yellowish-green in color and produce large amounts of pollen, while the female flowers are greenish-white in color and produce small, inconspicuous seeds.

Habitat and Distribution

Perennial ragweed is a common plant in North America, and it is found in a variety of habitats, including fields, roadsides, pastures, and disturbed areas. It is especially common in the Great Plains region of the United States, where it is often found in large, dense stands.

The plant is well-adapted to a variety of soil types, but it prefers sandy or loamy soils. It is also able to tolerate drought conditions and is able to grow in areas with low rainfall. Perennial ragweed is able to spread quickly and can form large colonies that can outcompete other plant species.

Allergenic Properties

One of the most significant characteristics of perennial ragweed is its ability to cause allergies in humans. The plant produces large amounts of pollen, which is highly allergenic and can cause symptoms such as sneezing, runny nose, itchy eyes, and asthma. The pollen is released into the air in late summer and early fall, and it can travel long distances, making it a major source of allergies for many people.

In addition to its pollen, perennial ragweed also produces a range of other allergenic compounds, including sesquiterpene lactones, which can cause skin irritation and contact dermatitis.

Management and Control

Because of its invasive nature and its ability to cause allergies, perennial ragweed is considered a nuisance plant by many people. It can be difficult to control, as it spreads quickly and can grow in a variety of conditions.

Several management strategies have been developed to control the spread of perennial ragweed, including the use of herbicides, mowing, and prescribed burning. Biological control methods have also been explored, but these have not been widely implemented.

In addition to these control strategies, it is also important for individuals to take steps to reduce their exposure to perennial ragweed pollen. This can include staying indoors during peak pollen times, wearing a mask when outside, and keeping windows and doors closed to prevent pollen from entering the home.


Perennial ragweed is a common plant in North America that is known for its invasive nature and its ability to cause allergies in humans. While it can be difficult to control, a range of management strategies have been developed to reduce its impact on the environment and on human health. By taking steps to control the spread of this plant and reduce exposure to its pollen, we can help to protect the health and well-being of ourselves and our communities.

More about Perennial Ragweed

Perennial ragweed is an important plant species in its native range, as it provides habitat and food for a variety of insects and animals. However, its invasive nature can cause it to outcompete native plant species, reducing biodiversity and altering local ecosystems.

The impact of perennial ragweed on human health is significant, as it is estimated to be responsible for up to 50% of all cases of hay fever in North America. In addition to causing respiratory symptoms, exposure to perennial ragweed pollen can also exacerbate existing conditions such as asthma and eczema.

The economic impact of perennial ragweed is also significant, as the cost of treating allergies and other health problems associated with the plant is estimated to be in the billions of dollars each year.

While the management and control of perennial ragweed is an important issue, it is also important to remember that the plant is a part of the natural world and has a role to play in local ecosystems. Efforts to control the spread of the plant should be balanced with efforts to preserve native plant species and the wildlife that depend on them.

Perennial ragweed is an important and complex plant species that plays a role in both the natural world and human health. While it can be a nuisance and a source of allergies, efforts to control its spread should be balanced with efforts to preserve local ecosystems and the well-being of humans and other animals.

One interesting aspect of perennial ragweed is its ability to adapt to changing environmental conditions. As a result, the plant is able to thrive in a wide range of habitats and can quickly colonize disturbed areas. This adaptability has made it a successful invasive species in many parts of the world.

Another important consideration in the management of perennial ragweed is the potential for the plant to develop resistance to herbicides. This has been observed in some areas where the plant is heavily managed, and it highlights the importance of using a variety of control strategies to minimize the impact of the plant.

Efforts to control the spread of perennial ragweed are often complicated by the fact that the plant produces a large amount of seed, which can remain viable in the soil for many years. This means that even if the above-ground portion of the plant is removed, the seeds can still germinate and give rise to new plants.

Despite these challenges, there are a number of ongoing efforts to manage the spread of perennial ragweed and reduce its impact on human health and the environment. These efforts involve collaboration between researchers, land managers, and community organizations, and they focus on a variety of strategies, including herbicide treatments, mowing, and the use of biological control agents.

Ultimately, the successful management of perennial ragweed will depend on a combination of effective control strategies, ongoing research into the biology of the plant, and public education and outreach to raise awareness of the importance of minimizing exposure to its allergenic pollen. By working together, we can help to protect the health of our communities and preserve the natural ecosystems that we depend on.

25 Perennial Ragweed Facts

  1. Botanical Name: Ambrosia psilostachya
  2. Habitat: Commonly found in prairies, open woodlands, and along roadsides.
  3. Height: Typically grows between 3 to 7 feet in height.
  4. Leaves: Feathery, finely divided leaves with a grayish-green hue.
  5. Flowers: Produces small, greenish flowers arranged in a spike-like inflorescence.
  6. Blooming Period: Blooms from late summer to fall.
  7. Allergenic Plant: Known to be a potent allergen, causing hay fever symptoms.
  8. Pollination: Relies on wind for pollination, contributing to its wide dispersal.
  9. Invasive Nature: Can be invasive and outcompete native vegetation.
  10. Geographic Distribution: Native to North America, particularly in central and eastern regions.
  11. Root System: Develops a deep and extensive root system.
  12. Medicinal Uses: Some Native American tribes historically used parts of the plant for medicinal purposes.
  13. Wildlife Habitat: Provides habitat and food for various insects and birds.
  14. Lifecycle: A perennial plant, living for more than two years.
  15. Adaptability: Thrives in a range of soil types, including clay and sandy soils.
  16. Ecological Impact: Can alter ecosystems and affect biodiversity in certain regions.
  17. Seed Production: Produces numerous seeds, contributing to its spread.
  18. Identification: Recognized by its tall stature, feathery leaves, and unique inflorescence.
  19. Sunlight Requirements: Prefers full sun but can tolerate partial shade.
  20. Drought Tolerance: Exhibits a degree of drought tolerance once established.
  21. Control Measures: Various methods, including controlled burns and herbicides, are used to manage its growth.
  22. Seasonal Changes: Undergoes noticeable changes in appearance during different seasons.
  23. Human Impact: Human activities and disturbance can contribute to its proliferation.
  24. Conservation Concerns: In some areas, efforts are made to control Ambrosia psilostachya to protect native ecosystems.
  25. Cultural Significance: May have cultural or historical importance in certain communities.

Distribution Map

Reproduced by kind permission of the BSBI.

Click to open an Interactive Map