Persicaria longiseta
(Bruijn) Kitag.
Common Name:
Oriental lady's thumb
Synonyms and Other Names:
Smartweed; Asiatic smartweed; Bristled knotweed; Bunchy knotweed; Long-bristled smartweed
Identification:
A summer annual weed of horticultural, agronomic, and nursery crops that may reach 3 1/2 feet in height. Seedlings: Cotyledons are elliptic to lanceolate in outline, whit hairs along the margins. First true leaves are alternate, lanceolate in outline, and hairy on the upper surfaces. Roots: Fibrous roots with a shallow taproot. Fruit: A black achene. Leaves: Arranged alternately along the stem, lanceolate to elliptic in outline, approximately 3/4 to 3 inches long and 1/2 to 1 1/4 inches wide. Older leaves are usually only slightly hairy. Leaves taper to short petioles, which have an ocrea that encircles the stem. Leaves often, but not always, have a purple spot in the middle of the leaf. Flowers: Flowers are clustered in terminal spikes at the ends of stems. Individual flowers are small and are dark pink to red in color.
The elliptic to lanceolate leaves with a purple spotted 'lady's thumb' print in the middle and distinctive ocrea with stiff hairs are all characteristics that help to distinguish tufted knotweed from other similar weeds.
Size:
3.5 feet
Native Range:
Native to Eastern Asia in China, Japan, India, Malaysia and Korea
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This map only depicts Great Lakes introductions.
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Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Persicaria longiseta are found here.
Table last updated 12/18/2020
† Populations may not be currently present.
Ecology:
Grows in moist soil and can grow in low light situations. It is often found in poor soils and can tolerate a wide range of pH (4.8 to 8). It can be found on ridge tops, open woods, trails, and roadsides near damp or wet places.
Means of Introduction:
Unknown.
Status:
Introduced – Naturalized
Great Lakes Impacts:
Remarks:
Pennsylvania Smartweed (Polygonum pensylvanicum) is very similar in appearance and growth habit, but does not have hairs on the ocrea like that of tufted knotweed. Ladys thumb (Polygonum persicaria) is also similar in appearance and growth habit, but has hairs on the ocrea that are much shorter (2 mm), and also has generally smaller leaves and dark pink to red flowers.
Synonyms: Persicaria longiseta; Polygonum longisetum
References
(click for full reference list)
Author:
Cao, L.
Contributing Agencies:
Revision Date:
10/21/2008
Citation for this information:
Cao, L., 2025, Persicaria longiseta (Bruijn) Kitag.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/GreatLakes/FactSheet.aspx?Species_ID=2735, Revision Date: 10/21/2008, Access Date: 1/15/2025
This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.