Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Persicaria punctata
(dotted smartweed)



Persicaria punctata (dotted smartweed)


  • Last modified
  • 20 November 2019
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Persicaria punctata
  • Preferred Common Name
  • dotted smartweed
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • P. persicaria is a species of knotweed native to the Americas. It has been introduced, presumably accidentally, to New Zealand, Pakistan and Hawaii, where it is found in shallow water, shores, marshes, swamps, the borders of ponds and sma...

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Preferred Scientific Name

  • Persicaria punctata (Elliott) Small

Preferred Common Name

  • dotted smartweed

Other Scientific Names

  • Persicaria persicarioides (Kunth) Small
  • Persicaria punctate var. eciliata Small
  • Polygonum acre Kunth
  • Polygonum epilobioides Wedd.
  • Polygonum punctatum Elliot
  • Polygonum punctatum var. aquatile (Mart.) Fassett
  • Polygonum punctatum var. confertiflorum (Meisn.) Fassett
  • Polygonum punctatum var. ellipticum Fassett
  • Polygonum punctatum var. leptostachyum (Meisn.) Small
  • Polygonum punctatum var. parviflorum Fassett
  • Polygonum punctatum var. parvum Vict. & J. Rousseau
  • Polygonum punctatum var. punctatum Elliott

Local Common Names

  • English: arse-smart; tar-weed; turkey-troop; water smartweed
  • French: piment-vache; renouee ponctuee
  • Spanish: ananash; barbasco; hierba del bicho; padilla; yerba caiman; yerba de sap
  • Brazil: erva-de-bicho-pontuada

Summary of Invasiveness

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P. persicaria is a species of knotweed native to the Americas. It has been introduced, presumably accidentally, to New Zealand, Pakistan and Hawaii, where it is found in shallow water, shores, marshes, swamps, the borders of ponds and small streams, drainage ditches and floodplain forests.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Polygonales
  •                         Family: Polygonaceae
  •                             Genus: Persicaria
  •                                 Species: Persicaria punctata

Notes on Taxonomy and Nomenclature

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Missouri Botanical Garden (2014) listed three varieties: Persicaria punctata var. robustior (Small) Small, Persicaria punctata var. eciliata Small and Persicaria punctata var. tacubayana Nieuwl.

Fassett (1949) proposed a complicated classification for Persicaria punctata comprising 12 varieties in North and South America. He also identified numerous specimens that he considered to be morphologically intermediate between various varieties. Dalci (1972, cited in Flora of North America, 2013) documented a wide range of phenotypic and genotypic variation throughout the range of P. punctata and extensive overlap in many of the features used by Fassett to distinguish varieties. Consequently, recognition of varieties does not seem warranted (Flora of North America, 2013).


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Slightly modified from Flora of North America (2013):

Plants are annual or perennial, 15-120 cm; roots also often arising from proximal nodes; rhizomes often present.

Stems are ascending to erect, branched, without noticeable ribs, glabrous, glandular-punctata. 

Leaves are ochre brown, cylindric, (4-)9-18 mm, chartaceous, base inflated, margins truncate, ciliate with bristles 2-11 mm, surface glabrous or strigose, glandular-punctata; petiole 0.1-1 cm, glandular-punctata, leaves sometimes sessile; blade without dark triangular or lunate blotch adaxially, lanceolate to lanceolate-ovate or subrhombic, 4-10(-15) by 0.6-2.4 cm, base tapered or cuneate, margins antrorsely strigose, apex acute to acuminate, faces glabrous or scabrous along midveins, glandular-punctata. 

Inflorescences are mostly terminal, sometimes also axillary, erect, interrupted, 50-200 by 4-8 mm; peduncle 30-60 mm, glabrous, glandular-punctata; ocreolae mostly not overlapping, margins mostly ciliate with bristles to 2 mm. Pedicels ascending, 1-4 mm. 

Flowers 2-6 per ocreate fascicle, homostylous; perianth greenish proximally, white distally, rarely tinged pink, glandular-punctata with punctae ± uniformly distributed, scarcely accrescent; tepals 5, connate ca. 1/ 3 their length, obovate, 3-3.5 mm, veins prominent or not, not anchor-shaped, margins entire, apex obtuse to rounded; stamens 6-8, included; anthers pink or red, elliptic to ovate; styles 2-3, connate proximally. 

Achenes included or apex exerted, brownish black, usually 3-gonous, rarely biconvex, (1.8-)2.2-3.2 by 1.5-2.2 mm, shiny, smooth.

Plant Type

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Seed propagated


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P. punctata is native to most of the Americas, from Canada to Chile and including the Caribbean. It is found in all but 13 of the mainland US states and in most Canadian provinces. It is also native to many South and Central American countries. In Illinois, it is described by Illinois Wildflowers (2013) as one of the more common smartweeds in wetland areas.

P. punctata has been introduced to New Zealand, Pakistan and Hawaii, where it is found in shallow water, shores, marshes, swamps, the borders of ponds and small streams, drainage ditches and floodplain forests.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Last updated: 10 Feb 2022
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes


PakistanPresent, Few occurrencesIntroducedReported from N.W.F province from Akbarpur, B. L. Burtt 1045, 1052 (E). Seems to be a rare species.

North America

CanadaPresentPresent based on regional distribution.
-British ColumbiaPresentNative
-New BrunswickPresentNative
-Nova ScotiaPresentNative
-Prince Edward IslandPresentNative
Cayman IslandsPresentNative
Costa RicaPresentNative
El SalvadorPresentNative
Puerto RicoPresentNative
Saint LuciaPresentNative
Saint Vincent and the GrenadinesPresentNative
United StatesPresentNative
-District of ColumbiaPresentNative
-HawaiiPresentIntroduced1909As: Polygonum punctatum
-New HampshirePresentNative
-New JerseyPresentNative
-New MexicoPresentNative
-New YorkPresentNative
-North CarolinaPresentNative
-North DakotaPresentNative
-Rhode IslandPresentNative
-South CarolinaPresentNative
-South DakotaPresentNative
-West VirginiaPresentNative


New ZealandPresent, WidespreadIntroducedInvasive

South America

French GuianaPresentNative

History of Introduction and Spread

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There is little or no information on how P. punctata was introduced to New Zealand and Pakistan. The first record of it in New Zealand was in 1976 (Webb et al., 1988).


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P. punctata grows in shallow water, shores, marshes, swamps, the borders of ponds and small streams, drainage ditches and floodplain forests (Illinois Wildflowers, 2013). This plant is often found along the edge of stagnant or slow-moving water, and appears to favour degraded wetlands. It grows at altitudes of 0-1500 m above sea level (Flora of North America, 2013). In Illinois, USA, P. punctata occurring in flood-prone areas of woodlands. In New Zealand, it is found in wet places such as swamps, ditches, lakesides and streamsides (Webb et al, 2013); similarly, in Hawaii it is found ‘naturalized along streambeds, wet areas, in running or standing water, and in disturbed wet forest’ (Wagner et al., 1999, cited in PIER, 2013).

Biology and Ecology

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Little has been reported on the biology or ecology of P. punctata, but the species is similar in appearance and habitat to the cosmopolitan species P. hydropiper, whose biology may be similar.


2n = 44 (Flora of North America, 2013).


In North America P. punctata is described by Flora of North America (2013) as annual or perennial, but there seems to be no information on how long plants can live for.

Activity patterns

In the United States, P. punctata flowers between June and November (Flora of North America, 2013).

Population size and structure

Illinois wildflowers (2013) reported that P. persicata ‘often forms colonies of varying size in wet areas’.

Associated species

According to Illinois Wildflowers (2013), short-tongued Halictid bees, various kinds of wasps, Syrphid flies and other kinds of flies, and the occasional beetle, including ladybirds, are attracted to the nectar of P. punctata. Halictid bees also collect pollen.


Environmental requirements

P. punctata seems to require moist soil or even shallow standing water (Flora of North America, 2013). 

Notes on Natural Enemies

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At least in Illinois, USA, caterpillars of the butterflies Lycaena hyllus (bronze copper) and Lycaena helloides (purple copper) feed on the foliage, as do the caterpillars of several moth species and the adults of the leaf beetle Gastrophysa polygoni (Illinois Wildflowers, 2013). The same source lists the larvae of the moths Lithocodia carneola, L. synochitis, Orthonoma centrostrigaria, O. obstipata, Acronicta oblinita, Pyrrhia experimens, Dipteryia rosmani, Xanthotype sospeta, Haematopis grataria and Nomophila neararctica as herbivores that feed on the foliage of  Persicaria species.

Means of Movement and Dispersal

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Natural dispersal (non-biotic)

P. punctata has no means of vegetative spread and the seeds are not adapted for dispersal other than by floating in water.

Vector transmission (biotic)

The seeds may be transported by mud on the feet of water birds, or possibly scattered by birds feeding on the seeds.

Accidental introduction

Presumably its introductions to countries well outside its native range were accidental, so further accidental introductions are always possible. 


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In the countries to which it has been introduced P. punctata seems to have had little impact so far, and is seen simply as another the introduced weedy species in wetland areas.

Risk and Impact Factors

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  • Proved invasive outside its native range
  • Has a broad native range
  • Tolerant of shade
  • Fast growing
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
  • Has high genetic variability


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Social benefit

The Chippewa, Houma, and Iroquois people of North America prepared decoctions from the leaves, flowers and roots of P. punctata for use as analgesics as well as gastrointestinal, orthopedic and psychological aids (Moerman, 1998, cited in Flora of North America, 2013).

In parts of Brazil the plant is used as a herb to treat intestinal disorders. De Almeida Alves et al. (2001) extracted the compound polygodial from aerial parts of the plant and found that it had strong fungitoxic activity. Since this compound also has antibiotic, anti-inflammatory and anti-hyperalgesic properties, it may account for the effects attributed to this species by folk medicine.

Environmental services

The seeds are eaten by many species of ducks, seed-eating rails and various songbirds, and may be a minor source of food to muskrats (Illinois Wildflowers, 2013). According to Hickman (2013), the species is planted as waterfowl food.


Similarities to Other Species/Conditions

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P. punctata and its close relatives P. robustior and P. glabra are unique among native North American smartweeds in possessing complex glands called valvate chambers in their epidermises.

P. punctata is confused most often with P. hydropiper (Flora of North America, 2013). Fassett (1949) noted that P. punctata shares with P. hydropiper the characteristic features of glandular dots on the perianth. However, P. punctata has smooth and shining rather than roughened and dull achenes and a strong tendency to longer internodes, less drooping spikes and less red colouring in the perianth.

Webb et al. (1988) experienced some slight difficulties with identifying the New Zealand material of P. punctata:  ‘Characters of the New Zealand plants put them closer to P. punctata than any other species, judging from descriptions in eFloras and from specimens. However, in the few American specimens examined, the fruits are smooth instead of being finely granular as in New Zealand plants, although they are more or less glossy in both cases. Otherwise, the tallness and robustness of the New Zealand plants mean that they also resemble descriptions of the American P. robustius (small) fern. Both species are related to the Old World P. hydropiper. Within New Zealand, North Island plants have deep green leaves, whereas South Island plants have yellowish green leaves, but the greater size of vegetative parts still distinguishes them all from P. hydropiper. Also, the only moderately peppery taste, the more or less tubular and appressed upper ochreae, white perianth, and obviously shining fruits usually distinguish P. punctatum from P. hydropiper.’

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Physical/mechanical control

Individual plants of P. punctata could be pulled or dug up, but this would not be recommended for large areas.

Biological control

The caterpillars of several moth species feed on Persicaria species in its native North America (see Notes on Natural Enemies; Illinois Wildflowers, 2013). However, P. punctata has not become a serious enough weed in its introduced range to warrant biological control yet.

Chemical control

Species of Persicaria can be controlled with glyphosate, 2,4-D, aminopyralid, clopyralid, dicamba, triclopyr or imazapyr, but all these compounds will adversely affect other plant species, including desirable species (DiTomaso et al., 2013).

Gaps in Knowledge/Research Needs

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There seems to be very little published information on the biology, ecology and associated species of P. punctata. More information on longevity of plants and seeds, environmental preferences and reproduction would be very useful.


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Alves TMde A; Ribeiro FL; Kloos H; Zani CL, 2001. Polygodial, the fungitoxic component from the Brazilian medicinal plant Polygonum punctatum. Memórias do Instituto Oswaldo Cruz, 96(6):831-833.

Dalci M, 1972. The taxonomy of section Persicaria (Tourn. in the genus Polygonum (Tourn. (Polygonaceae) in the United States east of the Rocky Mountains. dissertation. Nebraska, USA: University of Nebraska.

DiTomaso JM; Kyser GB, 2013. Lady's thumb and pale smartweed. Weed control in natural areas in the western United States. California, USA: Weed Research and Information Centre, University of California, 544 pp.

Fassett NC, 1949. The variation of Polygonum punctatum. Brittonia, 6(4):369-393.

Flora of North America, 2013. Flora of North America. FNA.

Flora of Pakistan Editorial Committee, 2013. Flora of Pakistan, eFloras website. St. Louis, Missouri and Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria.

GBIF, 2015. Global Biodiversity Information Facility.

Hickman JC, 2013. Polygonaceae: Buckwheat Family. Treatment from the Jepson Manual.

Homeopathic Materia Medica, 2013. Polygonum punctatum. International Academy of Classical Homeopathy.

Illinois Wildflowers, 2013. Water Smartweed: Persicaria punctate. Wetland Wildflowers.

Invasiveorg, 2013. Dotted smartweed: Persicaria punctata (Ell.) Small. Invasive and Exotic Species of North America.

ITIS, 2013. Integrated Taxonomic Information System (ITIS). Washington, DC, USA: Smithsonian Institution/NMNH.

Justice OL, 1941. A study of dormancy in seeds of Polygonum. Agricultural Experiment Station. Memoir, No. 235. 43 pp.

Missouri Botanical Garden, 2014. Tropicos database. St. Louis, Missouri, USA: Missouri Botanical Garden.

Moerman DE, 1998. Native American Ethnobotany. Oregon, USA: Timber Press, 927 pp.

New Zealand History online, 2012. US forces in New Zealand.

PIER, 2013. Pacific Islands Ecosystems at Risk. Honolulu, Hawaii, USA: HEAR, University of Hawaii.

Swearingen JM, 2013. Survey of invasive plants occurring on National Park Service lands, 2000-2007.

Timson J, 1996. Polygonum hydropiper L. Journal of Ecology, 54:815-821.

USDA-ARS, 2013. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory.

USDA-NRCS, 2013. The PLANTS Database. Baton Rouge, USA: National Plant Data Center.

Wagner WI; Herbst DR; Sohmer SH, 1999. Manual of the Flowering Plants of Hawaii, revised edition. Honolulu, Hawaii, USA: University of Hawaii Press.

Webb CJ; Sykes WR; Garnock-Jones PJ, 1988. Flora of New Zealand Volume IV. Naturalised Pteridophytes, Gymnosperms and Dicotyledons. Christchurch, New Zealand: DSIR Botany Division, 1365 pp.

Distribution References

CABI, Undated. CABI Compendium: Status inferred from regional distribution. Wallingford, UK: CABI

Flora of North America, 2013. Flora of North America., FNA.

Flora of Pakistan Editorial Committee, 2013. Flora of Pakistan. In: eFloras website, St. Louis, Missouri; Cambridge, Massachusetts, USA: Missouri Botanical Garden and Harvard University Herbaria.

GBIF, 2014. GBIF data portal., Copenhagen, Denmark: Global Biodiversity Information Facility (GBIF).

PIER, 2013. Pacific Islands Ecosystems at Risk., Honolulu, Hawaii, USA: HEAR, University of Hawaii.

Seebens H, Blackburn T M, Dyer E E, Genovesi P, Hulme P E, Jeschke J M, Pagad S, Pyšek P, Winter M, Arianoutsou M, Bacher S, Blasius B, Brundu G, Capinha C, Celesti-Grapow L, Dawson W, Dullinger S, Fuentes N, Jäger H, Kartesz J, Kenis M, Kreft H, Kühn I, Lenzner B, Liebhold A, Mosena A (et al), 2017. No saturation in the accumulation of alien species worldwide. Nature Communications. 8 (2), 14435.

USDA-ARS, 2013. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory.

USDA-NRCS, 2013. The PLANTS Database. Greensboro, North Carolina, USA: National Plant Data Team.

Webb CJ, Sykes WR, Garnock-Jones PJ, 1988. Flora of New Zealand. Naturalised Pteridophytes, Gymnosperms and Dicotyledons., IV Christchurch, New Zealand: DSIR Botany Division. 1365 pp.


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Original text by:

Ian Popay, consultant, New Zealand, with the support of Landcare Research.

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