Invasive Species: Polygonum caespitosum, Oriental Ladysthumb
Oriental ladysthumb is an invasive annual forb that can reach 6 to 30 in. (15.2 to 76.2 cm) in height and can be either erect or sprawling. Leaves are elongate, narrow, and pointed at the base and tip. Stems have swollen nodes with papery sheaths (ocrea). Ocrea have long, hair-like bristles on the margin. Flowering occurs from June to October, when pink flowers develop at the apex of the stems. Flowers are 1/8 in. (0.3 cm) long and occur in groups. The fruit is a trigonous black achene. Oriental ladysthumb is native to Asia and occurs in disturbed habitats such as along roadsides and in pastures. Plants also inhabit wet areas.
What are invasive species and why should we be concerned about them?
Taxonomy: Scientific and Common Names for This Species
Polygonales > Polygonaceae > Polygonum caespitosum Blume
Synonym(s): Persicaria longiseta, Asiatic smartweed, bristled knotweed, bunchy knotweed
Polygonum caespitosum – USDA PLANTS Profile
Distribution Maps
Oriental ladysthumb – The reported distribution of this invasive species across the United States (Source: Invasive Plant Atlas of the United States)
Up-to-the-minute distribution maps and why they are important
Reporting This Invasive Species
What is the best way and place to report the occurrence of an invasive species?
How to report an invasive species sighting to EDDMapS – Early Detection & Distribution Mapping System
EDDMapS – Report an invasive species to EDDMapS.
Cooperative Extension Offices – Find your local Cooperative Extension office on this map provided by USDA.
How to Identify
This invasive species can be identified by looking for the characteristics described in the paragraphs that follow.
Plant
Oriental ladysthumb is an annual forb that can reach 6 to 30 in. (15.2 to 76.2 cm) in height and can be either erect or sprawling.
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| Leslie J. Mehrhoff, University of Connecticut, bugwood.org | Leslie J. Mehrhoff, University of Connecticut, bugwood.org |
Foliage
Leaves are elongate, narrow, and pointed at the base and tip. Stems have swollen nodes with papery sheaths (ocrea). Ocrea have long, hair-like bristles on the margin.
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| Leslie J. Mehrhoff, University of Connecticut, bugwood.org | Chris Evans, River to River CWMA, bugwood.org |
Flower
Flowering occurs from June to October, when pink flowers develop at the apex of the stems. Flowers are 1/8 in. (0.3 cm) long and occur in groups.
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| Leslie J. Mehrhoff, University of Connecticut, bugwood.org | Leslie J. Mehrhoff, University of Connecticut, bugwood.org |
Fruit
The fruit is a trigonous black achene.
| bugwood.org | bugwood.org |
Native Species That Can Resemble Oriental Ladysthumb
Persicaria hydropiperoides, swamp smartweed – Bugwood.org
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| Ohio State Weed Lab Archive, The Ohio State University, bugwood.org | Joseph M. DiTomaso, University of California – Davis, bugwood.org |
Polygonum pensylvanicum , Pennsylvania smartweed – Bugwood.org
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| Dan Tenaglia, Missouriplants.com, bugwood.org | Dan Tenaglia, Missouriplants.com, bugwood.org |
Additional Images for Oriental Ladysthumb
Oriental ladysthumb – Images at Invasive.org
Learning Resources for Oriental Ladysthumb
Additional Information, Biology, Control and Management Resources
Control and management recommendations vary according to individual circumstances. Location, habitat, weather, and a variety of other conditions are factors that help determine the best treatment choice. To find the safest and most effective treatment for your situation, consult your state’s land-grant institution. If you will use chemicals as part of the control process, always refer to the product label.
United States Land-Grant University System – Find your land-grant university’s college of agriculture, Cooperative Extension office, or other related partner on this map provided by USDA.
Fire Effects Information System – US Forest Service
Invasive Plant Atlas of New England – University of Connecticut
Weed of the Week – US Forest Service