Polygonum caespitosum var. longisetum (deBruyn) A.N.Steward

Polygonum caespitosum var. longisetum (deBruyn) A.N.Steward
Bristly Lady's Thumb, Bunchy Knotweed, Long-bristled Smartweed, Oriental Lady's Thumb

Category
Forb/Herb

Description

Stem

The stems can be erect or prostrate, freely branched, reddish in color and swollen at the nodes.

Leaves

Thin, dark green leaves are alternately arranged and lanceolate to elliptic in shape. They measure 0.75 to 3 inches (2 to 7.5 cm) long and 0.5 to 1.25 inches (1 to 3 cm) wide. Foliage is mostly glabrous, but older leaves can sometimes have hairs on the margins and veins of the lower leaf surface.

Flowers

Flowers are clustered in terminal spikes at the ends of stems. Individual flowers are small, 0.75 to 1.5 inches (2 to 3.5 cm) in length and 0.2 inches (0.5 cm) across, and are dark pink to red in color. The flowers appear from July to October.

Fruit

The black, smooth, shiny acheneâ€™s are 0.07 to 0.1 inches (0.02 to 0.25 cm) in size and are dispersed mechanically. The roots are fibrous with a shallow taproot.

Images

Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
More images of Polygonum caespitosum

Life History

Polygonum caespitosum is a slender herbaceous annual in the Buckwheat family, native to Asia. It thrives in moist habitats and dominates the substrate, nutrients, water and sunlight to the detriment of native species. It is a moderately invasive plant.

Habitat

Roadsides, damp or wet places.

Origin and Distribution

Oriental Ladysthumb is prevalent in the eastern half of the United States as far west as New Mexico, Iowa and Nebraska.

Management Recommendations

Current literature suggests Polygonum caespitosum is restricted to disturbed areas and is not invasive in undisturbed habitat. Consequently, one method of management is to maintain a healthy natural community.

Mechanical Control

The best control method is to pull plants manually. This is especially effective after a good soaking rain. Frequent mowing where appropriate is helpful.

Chemical Control

This species can be effectively controlled using any of several readily available herbicides such as glyphosate. Use herbicides approved for aquatic application; follow label and state requirements.