Fact Sheets


Ambrosia psilostachya DC.

Family :

Famille :


Synonym(s) :

Synonyme(s) :

Common Name(s) :

Nom(s) commun(s) :

Perennial ragweed

  • Perennial ragweed (Ambrosia psilostachya) burs

  • Perennial ragweed (Ambrosia psilostachya) burs

  • Perennial ragweed (Ambrosia psilostachya) bur

  • Perennial ragweed (Ambrosia psilostachya) bur wall partially removed showing achene

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Regulation :

Remarques Réglementation:

  • Quarantine lists of countries e.g. India *may be updated without notice

Regulation Notes:

On quarantine lists of countries e.g. India*.

*Quarantine lists of countries may be updated without notice.

Distribution :

Répartition :

This species is native to North America (USDA-ARS 2017). It was introduced to some parts of Africa, Australia, Europe and Brazil (USDA-ARS 2017). In the United States, it is widespread, especially in central and mid-western states (USDA NRCS 2017).

Habitat and Crop Association :

Habitat et Cultures Associées :

Perennial ragweed occurs in dry sandy or rocky soils, abandoned fields, open prairie, forest openings, vacant lots, roadsides, railway embankments and other disturbed areas (Basset and Crompton 1975; Darbyshire 2003).

Economic Use, cultivation area, and Weed Association :

Utilisation économique, zone de culture et association de mauvaises herbes :

Duration of Life Cycle :

Durée du cycle vital:


Dispersal Unit Type :

Type d’unité de dispersion :

Achene within a bur

General Information


This species does not generally occur in production fields but can form large patches in disturbed areas from creeping rootstock. It is similar in appearance to common ragweed but is distinguished by a perennial habit and horizontal creeping root system, as opposed to an annual habit and tap-root system (Basset and Crompton 1975).


Ambrosia psilostachya plant (Joseph M. DiTomaso, University of California – Davis, Bugwood.org)



  • Bur


    • Bur length: 2.4 – 4.6 mm (average: 3.3 mm); width: 1.8 – 3.2 mm (average: 2.6 mm)


    • Bur and achene are both egg-shaped
    • Bur has a short, thick peg at the top of the wide end

    Surface Texture

    • Bur is woody and smooth with a ring of warts or tubercles near the wide end; may be absent in some burs


    • Bur is dull, light brown to grey-brown
  • Achene

    Surface Texture

    • Achene surface is smooth


    • Achene is slightly shiny, medium brown

Identification Tips


Additional Botany Information


Similar Species


Similar species are based on a study of seed morphology of various species, and those with similar dispersal units are identified. The study is limited by physical specimen and literature availability at the time of examination, and possibly impacted by the subjectivity of the authors based on their knowledge and experience. Providing similar species information for seed identification is to make users aware of similarities that could possibly result in misidentification.

Ambrosia artemisiifolia (common ragweed)

Common ragweed burs are a similar egg shape and greyish colour as perennial ragweed.

Common ragweed burs are generally smaller (average length: 2.9 mm; average width: 2.1 mm) have thin spines in a ring around the wide end and a thicker, pointed spike at the top of the wide end. Many common ragweed burs have purple streaks.

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Bassett, I.J. and Crompton, C.W. 1975. The Biology of Canadian weeds. 11. Ambrosia artemisiifolia L. and A. psilostachya DC. Canadian Journal of Plant Science 55: 463-476.

Darbyshire, S. J. 2003. Inventory of Canadian Agricultural Weeds. Agriculture and Agri-Food Canada, Research Branch. Ottawa, ON.

Flora of North America (FNA) Editorial Committee, eds. 1993+. Flora of North America North of Mexico [Online]. 22+ vols. New York and Oxford.  Accessed December 29, 2022.

Global Biodiversity Information Facility (GBIF) Secretariat. 2022. https://doi.org/10.15468/39omei Accessed via https://www.gbif.org/species/3110686 Accessed December 29, 2022.

U.S. Department of Agriculture-Agricultural Research Services (USDA-ARS). 2017. Germplasm Resources Information Network (GRIN), https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch Accessed April 25, 2017.

U.S. Department of Agriculture-Natural Resources Conservation Service (USDA-NRCS). 2017. The PLANTS Database. National Plant Data Team, Greensboro, NC USA. https://plants.usda.gov/home Accessed April 25, 2017.



Jennifer Neudorf, Angela Salzl, Ruojing Wang, Karen Castro, Katrina Entwistle

Canadian Food Inspection Agency