Polygonum douglasii is a species of flowering plant in the knotweed family known by the common name Douglas's knotweed. It is native to much of northern and western North America, where it can be found in many types of habitat, including disturbed areas.
The plant is variable in morphology and the subspecies are often difficult to distinguish. In general, plants in this complex are annual herbs growing erect to maximum heights anywhere between 3 and 80 centimeters with thin, angular stems. High-elevation plants are smaller and may be decumbent in form. The leaves are linear or widely lance-shaped, sometimes falling away to leave the plant mostly naked in flowering, or reduced to tiny scales at the stem tips. The flowers are a few millimeters long, pink to white in color, sometimes remaining closed or opening together in a clusterlike inflorescence.
- Flora of North America
- Costea, M. & F. J. Tardif. (2005). Taxonomy of the Polygonum douglasii (Polygonaceae) complex with a new species from Oregon. Brittonia 57:1 1-27.
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