Polygonaceae

Douglas' knotweed

Polygonum douglasii Greene

Family: Polygonaceae
Genus: Polygonum

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Douglas' knotweed (Polygonum douglasii) — FlowerPhoto: Alissa Iverson, CC BY 4.0, from iNaturalist

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Common names

By language (3)

English: Douglas' knotweed
nv: Kétłʼáhí
Ukrainian: Гірчак гірський

Synonyms

Polygonum douglasii var. douglasii
Polygonum douglasii var. latifolium (Engelm.) Greene
Polygonum montanum (Small) Greene
Polygonum tenue var. commune Engelm.
Polygonum tenue var. latifolium Engelm.

Flowers

In flower: July to October (from 41 flowering iNaturalist observations worldwide)

Characteristics

Growth habit: Forb/herb
Lifespan: Annual
In the US and Canada: Canada: native, Lower 48 states: native

Photos

FlowerPhoto: Alissa Iverson, CC BY 4.0, from iNaturalist
FlowerPhoto: Alissa Iverson, CC BY 4.0, from iNaturalist
FlowerPhoto: Daughter Dad, CC BY 4.0, from iNaturalist
FlowerPhoto: Bobby McCabe, CC BY 4.0, from iNaturalist
Photo: Matt Lavin, CC BY-SA 2.0, from Wikimedia Commons
Photo: Eric Schmidt, CC BY 4.0, from iNaturalist
Photo: Rob Foster, CC BY 4.0, from iNaturalist
Photo: Matt Lavin, CC BY-SA 2.0, from Wikimedia Commons
Photo: Dominic Gentilcore, CC BY 4.0, from iNaturalist
Photo: Matt Lavin from Bozeman, Montana, USA, CC BY-SA 2.0, from Wikimedia Commons
Photo: Steve Matson, CC BY 4.0, from iNaturalist
Photo: Matt Lavin from Bozeman, Montana, USA, CC BY-SA 2.0, from Wikimedia Commons

More in Polygonum

Sources: classification, synonyms from World Flora Online Plant List (2026-06, CC0 1.0); common names, popularity from Wikidata (2026-10-26, CC0 1.0); common names, US characteristics from USDA PLANTS Database (2025-05-29, CC0 1.0). About our plant data.