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Polygonum ramosissimum - bushy knotweed

Scientific Family
Polygonaceae
Synonyms
Cnopos ramosissimum, Polygonum atlanticum, P. exsertum, P. interior, P.latum, P. leptocarpum, P. patulum, P. stevensii, P.triangulum
Other common names
yellow flower knotweed
tall knotweed
yellow knotweed
Plant type
Forbs and Subshrubs
Origin
Native
Lifecycle
Annual
Height
To about 3 feet
Riparian
Yes

Annual with mostly erect stems; often much branched above with yellowish-green or bluish-green foliage. Narrow leaves have jagged brown sheaths at their bases. Small clusters of greenish or yellowish flowers grow at the leaf bases on a spike-like stalk.

Stems mostly erect; leaves erect, narrow, reduced upward, tip pointed, sheath at base; flowers in small spike-like clusters scattered along stems at leaf bases, petals, sepals greenish, yellowish, margins greenish-yellow or yellow, rarely pink or white.

Habitat

Usually moist habitats. Sometimes found in saline areas or coastal marshes but more widespread inland.

Plant Community
Riparian
Low elevation
5000
High elevation
7000

Flower Characteristics

2 to 5 small flowers grow in erect clusters from the upper leaf axils (between the leaf and stem). Each flower is 5-parted, 1/8 inch long, with a deep lobe. The petals and petal-like sepals are joined at the base with the outer 3 longer than the inner 2.

Flower color
Greenish, yellowish, rarely pink or white
Flower shape
Regular
Tubular
No
First bloom month
July
Last bloom month
September
Flower clusters
Elongated

Leaf and Stem Characteristics

Stems are smooth often growing to about 3 feet but may be as tall as 6 feet. Leaves are flat and narrow with thickened joints or nodes at the base. Branch leaves are much smaller than those on the stem. A sheath (ocrea) is found at the base of the leaf.

Leaf type
Simple
Leaf color
Yellowish-green, bluish-green
Leaf shape
Narrow
Leaf margin
Smooth
Leaf attachment
Alternate
Leaves clasp
No
Leaf hairs
None
Spines
No

Fruit and Seed Characteristics

Fruit is about 1/8 inch, dry, oval, 3-angled, smooth to rough, shiny or dull, sometimes with small rounded projections on its surface. Fruit is enclosed in or longer than the petals and sepals. Late season fruits are common and larger growing to 3/4 inch.

Fruit type
Achene
Fruit color
Dark brown to black

Each fruit produces 1 seed. The fruit does not split open to release the seed when mature.