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Montana Field Guide

Montana Field Guides

Japanese Knotweed - Polygonum cuspidatum
Other Names:  Fallopia japonica

Noxious Weed: Priority 1B
Non-native Species

Global Rank: GNR
State Rank: SNA
* (see State Rank Reason below)

Agency Status
MNPS Threat Rank:
C-value: 0

External Links

State Rank Reason (see State Rank above)
Part of the Japanese Knotweed Complex
  • Details on Status Ranking and Review
    Japanese Knotweed (Polygonum cuspidatum) Conservation Status Review
    Review Date =
General Description
Dioecious, rhizomatous perennial. Stems erect, branched, 1–2 m. Leaves petiolate; the blades ovate, 8–20 cm long with pointed tips and a truncate base; stipules brown, glabrous, 4–6 mm long. Flowers apparently perfect but functionally unisexual, 5–7 mm long with a tubular base, numerous in stipulate, axillary panicles; pedicels spreading, 3–5 mm long; tepals white to pink. Achene shiny-brown, 2–4 mm long, 3-sided, enclosed by an inflated perianth (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Range Comments
BC to QC south to most of the US; introduced from Asia as a garden ornamental (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 22

(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)



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Citation for data on this website:
Japanese Knotweed — Polygonum cuspidatum.  Montana Field Guide.  .  Retrieved on , from