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Montana Field Guide

Montana Field Guides

Canada Horseweed - Conyza canadensis
Other Names:  Erigeron canadensis

Native Species

Global Rank: G5
State Rank: S5

Agency Status
MNPS Threat Rank:
C-value: 2

External Links

General Description
Taprooted annual. Stems erect, usually unbranched, 10–100 cm. Herbage glabrate to sparsely hirsute, especially on the leaf margins. Leaves cauline, alternate, linear-oblanceolate, 2–8 cm long, short-petiolate, dentate below. Inflorescence narrow to corymbiform, paniculate, leafy-bracted below. Heads numerous, radiate but apparently discoid; involucres campanulate, 2–5 mm high; phyllaries weakly imbricate in 2 to 4 series, green with a tan center and scarious margins, glabrate, linear-lanceolate; receptacle flat, glabrous. Ray flowers 20 to 30, female, white to pink; ligules up to 1 mm long. Disk flowers perfect, 8 to 25, yellow; corolla 2–3 mm long; tube shorter than the throat; style branch appendages deltoid. Pappus of capillary bristles. Achenes oblong, compressed, ca. 1 mm long, sparsely strigose (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Species Range
Montana Range


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

Observations in Montana Natural Heritage Program Database
Number of Observations: 141

(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)

Disturbed meadows grasslands, roadsides; plains, valleys (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Cope, M.G. 1992. Distribution, habitat selection and survival of transplanted Columbian Sharp-tailed Grouse (Tympanuchus phasianellus columbianus) in the Tobacco Valley, Montana. M.Sc. Thesis. Bozeman, Montana: Montana State University. 60 p.
    • Gobielle, J. 1992. The effects of fire on Merriam's turkey broad habitat in southeastern Montana. M.S. thesis, Montana State University, Bozeman. 61 pp.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Martinka, R.R. 1970. Structural characteristics and ecological relationships of male blue grouse (Dendragapus obscurus (Say)) territories in southwestern Montana. Ph.D Dissertation. Bozeman, MT: Montana State University. 73 p.
    • Rundquist, V.M. 1973. Avian ecology on stock ponds in two vegetational types in north-central Montana. Ph.D. Dissertation. Bozeman, MT: Montana State University. 112 p.
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Citation for data on this website:
Canada Horseweed — Conyza canadensis.  Montana Field Guide.  .  Retrieved on , from