[Knotweeds and Smartweeds: The Genera Bistorta, Fallopia, Persicaria and Polygonum in the Cascade Mountains of Oregon and Washington]

Cascade Knotweed, Cascades Polygonum

Polygonum cascadense

Cascades knotweed as seen along the Cone Peak Trail #3408, Willamette National Forest......July 17, 2023. Note that the stem leaves strongly overlap and that flowers can be seen much of the upper length of the stem.

Characteristics:

Cascades polygonum is a low, spreading annual with thin, angled, erect stems which may be single or several branched and that may arise from 5-12 cm high. The numerous leaves are narrowly oblanceolate to obovate, from 5-20 mm wide and 2-5 mm wide. The leaf narrows to a petiole-like, jointed base.

The flowers are found in the leaf axils, with 3-5 flowers per axil. The flowers are found along much of the length of the stem. Flowers are 5-lobed, the lobes oblong and from 2-2.5 mm long, white, with pink or green mid-stripes. 8 stamens and 3 stigmas are present per flower.

Habitat:

Cascades polygonum is found on dry, rocky slopes.

Range:

An Oregon plant, it is found in the Cascades from Lane County south to Klamath County.

In the Columbia River Gorge, it may be found between the elevations of 0'-800' from near Cascade Locks, OR east to adjacent to Dog Mt..

Cascades polygonum? as seen along the Eagle Creek Trail.......October 18, 2011 .Note that the stem leaves strongly overlap and that flowers can be seen much of the upper length of the stem.

What appears to be cascade knotweed as seen on basal cliffs along the Eagle Creek Trail, Columbia River Gorge..........August 2, 2012.

Cascade Knotweed, Cascades Polygonum: Polygonum cascadense

Cascades Polygonum?.....7/14/90.

Paul Slichter