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Weed Identification

Pennsylvania smartweed

Family

Polygonaceae

Scientific Name

Polygonum pensylvanicum

Other Common Names:

Pennsylvania knotweed
pinweed

Synonyms (former Scientific Names):

Polygonum mexicanum
Polygonum bicorne
Persicaria bicornis
Persicaria mississippiensis
Persicaria pensylvanica
Persicaria longistyla
Polygonum mississippiense
Polygonum longistylum

Habit

An up-right branched plant reaching heights of 1 to 4 feet with a shallow tap root and fibrous secondary roots. This species spreads by seed germinating in the early to late spring.

Leaves

Usually lance shaped with very short stalks and one prominent vein in the center.

Identifying Characteristics

This species has large nodes where each alternate leaf is attached with a papery sheath surrounding the attachment.

Flower Seed Head

Found in a spike-like terminal cluster, flowers are usually pink to white.

Seed Fruit

Achenes house the shiny, black, flat, tear-shaped seeds measuring 3 mm.

Where Found

Throughout the United States this plant is usually not a factor in turf. However, it plagues landscapes, horticultural, and agronomic crops as well as nurseries.

Growth Habit

upright and nonwoody

Thorns or Spines

not present

Approximate Flower Diameter

dime

Dominant Flower Color

pink

Flower Symmetry

radial symmetery

Leaf Hairs

has hairs

Leaf Shape

lance

Leaf Arrangement

alternate

Leaf Margin

entire

Leaf Structure

simple

Leaf Stalk

shorter than leaf

Stem Hairs

has hairs

Stem Cross Section

round or oval

Milky Sap

not present

Root Structure

taproot

Life Cycle

summer annual

Ochrea

present

Plant Type

Herb