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Polygonum douglasii
Polygonum douglasii (Douglas' Knotweed)
Polygonaceae (Buckwheat Family)

Foothills, montane, subalpine. Meadows, woodlands, disturbed areas. Summer, fall.
Colorado Trail near Roaring Fork Road, August 20, 2017.

Polygonum douglasii    Polygonum douglasii

Polygonum douglasii (Douglas' Knotweed)
Polygonaceae (Buckwheat Family)

Foothills, montane, subalpine. Meadows, woodlands, disturbed areas. Summer, fall.
Colorado Trail near Roaring Fork Road, August 20, 2017.

Polygonum douglasii is an annual that grows erect from 2 to 30 inches with a number of branches. It is a common, wide-spread plant (see the map below), but because of its slender habit, it is easily overlooked  --  especially when not flowering. It definitely was the white flowers that called my attention to this specimen.

The Polygonum genus was named by Linnaeus in 1753. "Polygonum" is Latin for "many" "knees", referring to the many swollen stem/leaf joints common to this genus.

Edward Greene named and described this species in 1885 from a specimen collected in 1868 in Nevada by Sereno Watson. David Douglas (of Douglas Fir fame) was highly regarded for his prowess as a plant collector. Click to read more about Douglas.

polygonum douglasii

Polygonum douglasii (Douglas' Knotweed)
Polygonaceae (Buckwheat Family)

Foothills, montane, subalpine. Meadows, woodlands, disturbed areas. Summer, fall.
Colorado Trail near Roaring Fork Road, August 20, 2017.

The corolla of Polygonum douglasii is multi-colored, containing various amounts of white, green, tan, and red.

The green of the mid-rib commonly spreads (as in these photographs) into intriguing leaf-like shapes.

The top arrow at left points to the single, 3-4 millimeter long, shiny, black seed.

The bottom arrow points to one of the swollen joints and to the long (6-12 mm) sheath (the "ocrea") which covers the joint.

Polygonum engelmannii is similar to P. douglasii, but has shorter seeds and shorter ocreas.

Polygonum douglasii

Polygonum douglasii (Douglas' Knotweed)
Polygonaceae (Buckwheat Family)

Foothills, montane, subalpine. Meadows, woodlands, disturbed areas. Summer, fall.
Colorado Trail near Roaring Fork Road, August 20, 2017.

Stems are 4-angled, erect, and often purple.

Leaves are usually glabrous and they vary, as in this photograph, from linear to oblanceolate to narrowly oblong.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Polygonum douglasii

Range map for Polygonum douglasii