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Montana Field Guide

Montana Field Guides

Marshpepper Smartweed - Polygonum hydropiper
Other Names:  Marshpepper Knotweed, Mild Water-pepper, Persicaria hydropiper

Non-native Species

Global Rank: GNR
State Rank: SNA
C-value: 1

Agency Status


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General Description
Glandular-punctate annual. Stems erect to prostrate, sometimes rooting at the nodes, branched, 8–80 cm. Leaves short-petiolate; the blades lanceolate to elliptic, 2–8 cm long; stipules brown, 5–15 mm long, papery, sparsely ciliate-margined. Flowers 2–4 mm long, in narrow terminal racemes 1–7 cm long; pedicels 1–3 mm long, ascending; tepals 4 to 5, densely glandular-punctate, green with white or pink margins, 3-veined. Achene 2- to 3-sided, 2–3 mm long, brown with a dull granular surface (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Species Range
Montana Range Range Descriptions


Range Comments
Throughout temperate North America; introduced from Europe (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 19

(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)

Mud along margins of wetlands, streams; plains, valleys. (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).)

The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus bifarius, Bombus flavifrons, Bombus frigidus, Bombus melanopygus, Bombus sylvicola, Bombus occidentalis, Bombus pensylvanicus, Bombus insularis, and Bombus kirbiellus (Macior 1974, Colla and Dumesh 2010).


  • Literature Cited AboveLegend:   View Online Publication
    • Colla, S.R. and S. Dumesh. 2010. The bumble bees of southern Ontario: notes on natural history and distribution. Journal of the Entomological Society of Ontario 141:39-68.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Macior, L.M. 1974. Pollination ecology of the Front Range of the Colorado Rocky Mountains. Melanderia 15: 1-59.
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Citation for data on this website:
Marshpepper Smartweed — Polygonum hydropiper.  Montana Field Guide.  .  Retrieved on , from