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Montana Field Guide

Montana Field Guides

Western Ragweed - Ambrosia psilostachya

Native Species

Global Rank: G5
State Rank: S4S5

Agency Status
MNPS Threat Rank:
C-value: 4

External Links

General Description
Rhizomatous perennial. Stems erect, simple or branched, 10–50 cm. Herbage strigose, sometimes glandular. Leaves opposite below; blade ovate, 2–8 cm long, once pinnatifid into dentate lobes. Female heads 1-flowered. Male heads cup-shape, 2–3 mm wide, hispid, glandular with 5 to 15 florets, spreading on peduncles up to 1 mm long. Bur 2–3 mm long, ovoid, glandular, hispid (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Species Range
Montana Range


Range Comments
Throughout North America (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 212

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)


  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Fritzen, D.E. 1995. Ecology and behavior of Mule Deer on the Rosebud Coal Mine, Montana. Ph.D. Dissertation. Bozeman, MT: Montana State University. 143 p.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Scow, K.L. 1981. Ecological distribution of small mammals at Sarpy Creek, Montana, with special consideration of the Deer Mouse, Peromyscus maniculatus. M.Sc. Thesis. Bozeman, Montana: Montana State University. 73 p.
  • Web Search Engines for Articles on "Western Ragweed"
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Citation for data on this website:
Western Ragweed — Ambrosia psilostachya.  Montana Field Guide.  .  Retrieved on , from