Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Polygonum arenastrum
(common knotweed)

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Datasheet

Polygonum arenastrum (common knotweed)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Polygonum arenastrum
  • Preferred Common Name
  • common knotweed
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • P. arenastrum is an annual species native to Eurasia. It is found in field and row crops, orchards, yards, gardens and turf. It readily invades areas compacted by trampling with foot traffic and is therefore fr...

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Pictures

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PictureTitleCaptionCopyright
Polygonum arenastrum (common knotweed); habit, showing leaves, stems and flowers. New Zealand.
TitleHabit
CaptionPolygonum arenastrum (common knotweed); habit, showing leaves, stems and flowers. New Zealand.
Copyright©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); habit, showing leaves, stems and flowers. New Zealand.
HabitPolygonum arenastrum (common knotweed); habit, showing leaves, stems and flowers. New Zealand.©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); habit. New Zealand.
TitleHabit
CaptionPolygonum arenastrum (common knotweed); habit. New Zealand.
Copyright©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); habit. New Zealand.
HabitPolygonum arenastrum (common knotweed); habit. New Zealand.©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); generala habit. New Zealand. December, 2004.
TitleHabit
CaptionPolygonum arenastrum (common knotweed); generala habit. New Zealand. December, 2004.
Copyright©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); generala habit. New Zealand. December, 2004.
HabitPolygonum arenastrum (common knotweed); generala habit. New Zealand. December, 2004.©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); habit, showing leaves, stems and flowers. New Zealand.
TitleHabit
CaptionPolygonum arenastrum (common knotweed); habit, showing leaves, stems and flowers. New Zealand.
Copyright©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); habit, showing leaves, stems and flowers. New Zealand.
HabitPolygonum arenastrum (common knotweed); habit, showing leaves, stems and flowers. New Zealand.©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); stem and leaves. New Zealand.
TitleStem and leaves
CaptionPolygonum arenastrum (common knotweed); stem and leaves. New Zealand.
Copyright©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); stem and leaves. New Zealand.
Stem and leavesPolygonum arenastrum (common knotweed); stem and leaves. New Zealand.©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); leaves and flowers. New Zealand.
TitleLeaves and flowers
CaptionPolygonum arenastrum (common knotweed); leaves and flowers. New Zealand.
Copyright©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); leaves and flowers. New Zealand.
Leaves and flowersPolygonum arenastrum (common knotweed); leaves and flowers. New Zealand.©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); close-up of flower and leaf. New Zealand.
TitleFower and leaf
CaptionPolygonum arenastrum (common knotweed); close-up of flower and leaf. New Zealand.
Copyright©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); close-up of flower and leaf. New Zealand.
Fower and leafPolygonum arenastrum (common knotweed); close-up of flower and leaf. New Zealand.©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); close-up of flower. New Zealand.
TitleFlower
CaptionPolygonum arenastrum (common knotweed); close-up of flower. New Zealand.
Copyright©Trevor James-2004/Hamilton, New Zealand
Polygonum arenastrum (common knotweed); close-up of flower. New Zealand.
FlowerPolygonum arenastrum (common knotweed); close-up of flower. New Zealand.©Trevor James-2004/Hamilton, New Zealand

Identity

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Preferred Scientific Name

  • Polygonum arenastrum Boreau

Preferred Common Name

  • common knotweed

Other Scientific Names

  • Polygonum acetosellum Klokov
  • Polygonum aequale Lindm.
  • Polygonum arenastrum subsp. calcatum (Lindm.) Wissk.
  • Polygonum arenastrum subsp. microspermum (Jord. Ex Boreau) H.Scholz
  • Polygonum aviculare subsp. aequale (Lindm.) Asch. & Graebn.
  • Polygonum aviculare subsp. calcatum (Lindm.) Thell.
  • Polygonum calcatum Lindm.
  • Polygonum ebracteatum Munshi & Javeid
  • Polygonum microspermum Jod. Ex Boreau
  • Polygonum montereyense Brenckle
  • Polygonum propinquum Ledeb.

International Common Names

  • English: bird grass; box knotweed; doorweed; dooryard knotweed; engelmann's knotweed; equal-leaved knotgrass; matgrass; matweed; ovalleaf knotweed; prairie knotweed; prostrate knotweed; sand wireweed; small leaved wireweed; small-leaved knotgrass; small-leaved knotweed; stonegrass; wiregrass; wireweed
  • Spanish: centidonia; ciennudillos; ciennudos; cordoncillo; corregüela; corregüela de los caminos; hierba de la golondrina; hierba de las calenturas; hierba de los cursos; hierba nudosa; hierba rastrera; hierba terrera; lanceta; lengua de pájaro; pasacaminos; pico de gorrión; polígono macho; sanguinaria; sanguinaria basta; sanguinaria mayor; saucejo; saucillo
  • French: renouée des graviers
  • Arabic: assa-er-rai
  • Chinese: fu di bian xu

Local Common Names

  • Czech Republic: truskavec obecný; truskavec ptací leskloplodý
  • Estonia: harilik linnurohi
  • Italy: poligono dei sabbioni
  • Latvia: maura surene
  • Lithuania: smulkialape takažole
  • Spain: centidònia; cordela; corretjola; herba; herba de cent nusos; odarra; odularra; pé de paxaro
  • Sweden: trampört

Summary of Invasiveness

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P. arenastrum is an annual species native to Eurasia. It is found in field and row crops, orchards, yards, gardens and turf. It readily invades areas compacted by trampling with foot traffic and is therefore frequently found along roadsides, sports fields, vacant lots, gravel parking areas and walkways. This species establishes a taproot, which allows it to survive periods of drought. As a result it can compete with agricultural crops for water and nutrients reducing yields. In California it is reported to have a negative impact on the threatened species Arenaria ursina [Eremogone ursina]. P. arenastrum is considered as an environmental weed in parts of Australia and an agricultural weed in cropping systems in Australia and Canada.

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

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The genus Polygonum belongs to the Polygonaceae family and owes its name to the Greek words poly (many) and gonu (knot), alluding to this plant’s stem formation (Johnson and Smith, 1972). This genus comprises 245 accepted and unresolved species (The Plant List, 2013).

Not unlike other species in the genus, many Polygonum species with a prostrate habit have been subject to several taxonomic classifications. Some authorities regard P. aviculare as a single polymorphic species with several subspecies (including P. arenastrum) (Hilty, 2015), while other authorities identify several distinct species of prostrate knotweed (McNeil, 1981; The Plant List, 2013). Often, agricultural publications use P. arenastrum and its morphologically related species P. aviculare (syn. P. monspeliense) exchangeablyAPG-III accepts each of those as separate species of their own (The Plant List, 2013).

P. arenastrum was first described by Alexandre Boreau in 1857. The Latin ephitet arenastrum means “from the sand” (Johson and Smith, 1972).

Description

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The following text is adapted from the Flora of China Editorial Committee (2015)P. arenastrum has procumbent or ascending stems, 15-30 cm tall, branched from base. Petiole is short, articulate at base. Leaf blade is elliptic or oblanceolate, 0.5-2 cm × 2-5 mm, both surfaces with conspicuous veins, base narrowly cuneate, margin entire, apex usually obtuse; ocrea white, 2-3 mm, membranous, 5-7 veined, lacerate. Flowers 3-5, grow in axillary fascicles; with narrowly ovate bracts and acute apex. Pedicel articulate at apex. Perianth is green, 5-cleft to 1/2, veined, margin white; tepals oblong. Stamens 8; filaments dilated at base. Styles 3, very short; stigmas capitate. Achenes (one-seeded fruit that does not open to release the seed) are included in persistent perianth, dark brown, opaque, narrowly ovoid, trigonous, rarely biconvex, 2-2.5 mm, densely minutely granular striate.

Plant Type

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Herbaceous
Seed propagated

Distribution

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P. arenastrum is an annual species native to Eurasia. This species has established itself throughout most of the USA, Canada, Mexico, Australia and New Zealand. In the African continent, is has been recorded in Zimbabwe and Morocco. 

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.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

AfghanistanPresentNativeGBIF, 2015
ArmeniaPresentGBIF, 2015
ChinaPresentNativeFlora of China Editorial Committee, 2015
IndiaPresentPresent based on regional distribution.
-Jammu and KashmirPresentNativeGBIF, 2015
IranPresentNativeGBIF, 2015
IsraelPresentNativeGBIF, 2015
JapanPresentPresent based on regional distribution.
-HonshuPresentNativeGBIF, 2015
JordanPresentNativeGBIF, 2015
Korea, Republic ofPresentNativeGBIF, 2015
NepalPresent1994NativeGBIF, 2015
TurkeyPresent1999NativeGBIF, 2015

Africa

MoroccoPresent1923GBIF, 2015
ZimbabwePresentIntroducedHyde et al., 2015

North America

CanadaPresentPresent based on regional distribution.
-AlbertaPresent2010IntroducedGBIF, 2015
-British ColumbiaPresent2001IntroducedGBIF, 2015
-ManitobaPresent2003IntroducedDarbyshire, 2003Listed as an agricultural weed
-New BrunswickPresent2003IntroducedDarbyshire, 2003Listed as an agricultural weed
-Newfoundland and LabradorPresent2003IntroducedDarbyshire, 2003Listed as an agricultural weed
-Northwest TerritoriesPresent2003IntroducedDarbyshire, 2003Listed as an agricultural weed
-Nova ScotiaPresent1996IntroducedGBIF, 2015
-NunavutPresent2003IntroducedDarbyshire, 2003Listed as an agricultural weed
-OntarioPresentIntroduced1975GBIF, 2015
-Prince Edward IslandPresent2005IntroducedGBIF, 2015
-QuebecPresentIntroduced1988GBIF, 2015
-SaskatchewanPresent2003IntroducedDarbyshire, 2003Listed as an agricultural weed
-Yukon TerritoryPresent2003IntroducedDarbyshire, 2003Listed as an agricultural weed
MexicoPresent1994Introduced1954GBIF, 2015
USAPresentPresent based on regional distribution.
-CaliforniaPresent1989Introduced1933GBIF, 2015
-ColoradoPresent1997Introduced1932GBIF, 2015
-IllinoisPresentIntroducedHilty, 2015
-MassachusettsPresentIntroduced1924GBIF, 2015
-MichiganPresent1996IntroducedGBIF, 2015
-MissouriPresent2001Introduced1932GBIF, 2015
-OregonPresent1997IntroducedGBIF, 2015
-UtahPresent1999Introduced1916GBIF, 2015
-WashingtonPresent1992IntroducedGBIF, 2015

Europe

AndorraPresent2008NativeGBIF, 2015
AustriaPresent1991NativeGBIF, 2015
CroatiaPresent1997NativeGBIF, 2015
DenmarkPresent1993NativeGBIF, 2015
EstoniaPresent2014NativeGBIF, 2015
FinlandPresentNativeGBIF, 2015
FrancePresent1994NativeGBIF, 2015
GermanyPresent1999NativeGBIF, 2015
GreecePresent1999NativeGBIF, 2015
HungaryPresent2014NativeGBIF, 2015
IrelandPresentNativeGBIF, 2015
ItalyPresentNativeGBIF, 2015
NetherlandsPresentNativeGBIF, 2015
NorwayPresentNativeGBIF, 2015
PolandPresent2006NativeGBIF, 2015
PortugalPresent1996NativeGBIF, 2015
Russian FederationPresentPresent based on regional distribution.
-Russian Far EastPresent2003NativeGBIF, 2015
SlovakiaPresentNativeGBIF, 2015
SloveniaPresent1997NativeGBIF, 2015
SpainPresentNativeGBIF, 2015
SwedenPresentNativeGBIF, 2015
SwitzerlandPresentNativeInfo Flora, 2015
UKPresentNativeGBIF, 2015

Oceania

AustraliaPresentPresent based on regional distribution.
-New South WalesPresent2005Introduced1931GBIF, 2015
-South AustraliaPresentIntroducedQueensland Government, 2015
-TasmaniaPresentIntroducedQueensland Government, 2015
-VictoriaPresentIntroduced Invasive Queensland Government, 2015
-Western AustraliaPresentIntroducedQueensland Government, 2015
New ZealandPresentIntroduced1940NZPCN, New Zealand Plant Conservation Network

Habitat

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P. arenastrum is found from sea level up to 2500 m. This species thrives on areas where other weeds may have difficulty surviving such as trampled and compacted areas. Examples include turf, roadsides, sports fields, vacant lots, gravel parking areas, gardens, agricultural crops, foot paths and dirt roadways. In turf it invades open areas caused by heavy wear (Smith et al., 2008). 

Habitat List

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CategoryHabitatPresenceStatus
Terrestrial-managed
Cultivated / agricultural land Principal habitat
Disturbed areas Principal habitat
Industrial / intensive livestock production systems Principal habitat
Managed grasslands (grazing systems) Present, no further details Natural
Rail / roadsides Principal habitat
Urban / peri-urban areas Principal habitat

Hosts/Species Affected

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Smith et al. (2008) note that P. arenastrum is troublesome in agricultural fields, in particular in alfalfa fields (Medicago sativa), where soil is compacted from wheel traffic. 

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Medicago sativa (lucerne)FabaceaeUnknown

Biology and Ecology

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Genetics

P. arenastrum has a chromosome number of 2n=4x=40 (McNeill, 1981).

Reproductive Biology

P. arenastrum is self-pollinated or pollinated by flower flies (Syrphidae) and small bees, who are attracted to the small flowers (Hilty, 2015). This species propagates by seed, which are produced numerously. According to Smith et al. (2008), the seeds of P. arenastrum, like other species in this genus, are likely to be long-lived. It has been suggested that the seed can remain viable for up to six years in the soil (Hook, 2013).

Physiology and Phenology

The seeds of P. arenastrum germinate from autumn to early summer, when sufficient moisture is available. In temperate climates, it grows slowly and upright before becoming prostrate. In warm weather, however, growth is rapid. Flowers are produced in the spring to summer, in the Northern hemisphere it flowers from May through October (UCIPM, 2014). Seeds develop on the plant low to the ground and seedlings readily survive mowing. (Smith et al., 2008).

During the spring P. arenastrum produces a large tap root which enables its survival during summer droughts.

Longevity

P. arenastrum is an annual or short-lived perennial plant.

Population Size and Structure

This species can form mats of up to one meter in diameter (Smith et al., 2008)

Environmental Requirements

This species occurs on a wide range of soils, but prefers loams and heavy alkaline soils that are slightly moist to dry and where there is little competition from other plants. It can be exposed to saline and polluted soils (such as those of roadsides) and tolerates a considerable amount of trampling (Smith et al., 2015). However, increasing salinity can reduce germination (Burnett and Moore, 2014). P. arenastrum tolerates a wide soil pH range from 5.6 to 8.4 (Burnett and Moore, 2014). It grows in full sun or partial shade.

Climate

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ClimateStatusDescriptionRemark
As - Tropical savanna climate with dry summer Tolerated < 60mm precipitation driest month (in summer) and < (100 - [total annual precipitation{mm}/25])
Aw - Tropical wet and dry savanna climate Tolerated < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
BS - Steppe climate Tolerated > 430mm and < 860mm annual precipitation
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Tolerated Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
Df - Continental climate, wet all year Preferred Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)
Ds - Continental climate with dry summer Tolerated Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Tolerated Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)

Soil Tolerances

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Soil drainage

  • free

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Special soil tolerances

  • infertile
  • saline

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Aphis polygonata Herbivore not specific
Aspidaphis adjuvans Herbivore not specific
Capitophorus hippophaes Herbivore not specific
Chaetocnema concinna Herbivore not specific
Grammia virguncula Herbivore not specific
Haematopis grataria Herbivore not specific
Nomophila nearctica Herbivore not specific
Nycterosea obstipata Herbivore not specific

Notes on Natural Enemies

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According to Hilty (2015), there are a number of insects that feed on the foliage, sap and other parts of Polygonum species. Natural enemies include the brassy flea beetle (Chaetocnema concinna), the aphids Aspidaphis adjuvans, Aphis polygonata and Capitophorus hippophaes and larvae of the moths Grammia virguncula, Haematopis grataria, Nomophila nearctica and Orthonama obstipata [Nycterosea obstipata] (Covell, 1984; Hilty, 2015).

Means of Movement and Dispersal

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Natural Dispersal

P. arenastrum produces a large number of seeds that are naturally shed and disperse locally from the parent plant. Wind and rain splash will also help to disperse seed (Hook, 2013).

Vector Transmission

The seeds of P. arenastrum are dispersed by draught animals, small mammals and birds. In Australia particularly, this species is dispersed by a number of waterfowls such as the grey teal (Anas gracilis), black swan (Cygnus atratus) and Eurasian coot (Fulica atra) (Green et al., 2008). In the USA, the ring-necked pheasant (Phasianus colchicus), mourning dove (Zenaida macroura) and cowbird (Molothrus spp.) to name but a few, will eat and disperse the seeds of this species (Martin et al., 1951). The white-footed mouse (Peromyscus leucopus) and house mouse (Mus musculus) are also known to eat and disperse seeds (Whitaker, 1966) in addition to horses, who will transport seeds in their digestive tract (Wells and Lauenroth, 2007).

Seeds are also known to be dispersed by machinary (Hook, 2013).

Accidental Introduction

There is a risk of propagule dispersal of P. arenastrum through produce contamination. For example, it is possible that seeds may accidentally introduced into a new area when mowing or dumping garden refuse.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Crop productionAccidental Yes Burnett and Moore, 2014
ForageIngested by horses used to transport people in recreational trails Yes Wells and Lauenroth, 2007
Garden waste disposal Yes Burnett and Moore, 2014

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
LivestockSeeds Yes Wells and Lauenroth, 2007
Machinery and equipmentSeeds Yes Burnett and Moore, 2014
Waterrain splash Yes Hook, 2013
Wind Yes Hook, 2013

Impact Summary

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CategoryImpact
Economic/livelihood Negative
Environment (generally) Negative

Economic Impact

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Due to its potential as a seed contaminant, P. arenastrum is considered amongst the world’s most economically important weeds (Wiersema and León, 1999) and is considered one of the top 20 weeds of broadacre cropping systems in Australia (V. Burnett, personal communication, Department of Economic Development, Jobs, Transport and Resources, Australia, 2015).

P. arenastrum is a weed of agricultural crops with seeds germinating during crop establishment (Darbyshire, 2003). It is also a significant resevoir for the parasitic weed dodder (Cuscuta campestris) and other pathogens such as powdery mildew fungi (Erysiphe spp.) (Smith et al., 2008). Therefore P. arenastrum indirectly affects crops such as alfalfa (Medicago sativa), tobacco (Nicotiana tabacum), potato (Solanum tuberosum), lentil (Lens esculenta [Lens culinaris]), parsnip (Pastinaca sativa) onion (Allium cepa) and sugar beet (Beta vulgaris) (Toth et al., 2006).

In addition to this the long, tough branches of P. arenastrum can become tangled in cultivation equipment, causing blockages and interfering with harvesting operations and encouraging seed spread (Burnett and Moore, 2014).

Environmental Impact

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Burnett and Moore (2014) note that P. arenastrum and P. aviculare produce phytotoxic chemicals that can inhibit the establishment of other plant species, especially black medic (Medicago lupulina) and alfalfa (M. sativa). They are also known to affect rhizobium bacteria required for legume nodulation (Burnett and Moore, 2014). In addition to this it competes with crop species for nutrients and water and its large tap root enables it to survive during long periods of drought (Burnett and Moore, 2014). As a result this causes a reduction in crop yields.

P. arenastrum is also reported to be impacting on the broom flat pebble plain complex in California and competing with Arenaria ursina [Eremogone ursina] a species listed as threatened according to the US Fish and Wildlife Service (2015)

Threatened Species

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Threatened SpeciesConservation StatusWhere ThreatenedMechanismReferencesNotes
Eremogone ursina (Bear Valley sandwort)NatureServe NatureServe; USA ESA listing as threatened species USA ESA listing as threatened speciesCaliforniaUS Fish and Wildlife Service, 2007

Risk and Impact Factors

Top of page Invasiveness
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
  • Has high genetic variability
Impact outcomes
  • Negatively impacts agriculture
Impact mechanisms
  • Competition - monopolizing resources
  • Pest and disease transmission
  • Herbivory/grazing/browsing
  • Induces hypersensitivity
  • Interaction with other invasive species
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult/costly to control

Uses

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Social Benefit

P. arenastrum is an edible plant that can be eaten raw or cooked (Bown, 1995). The seeds can be used in the same manner as buckwheat (Fagopyrum esculentum), either whole or dried and ground into flour (Harris, 1968; Facciola, 1990). The leaves are a tea substitute (Facciola, 1990).

The roots of this species contain tannins (Rottsieper, 1946) and blue, green and yellow dyes can be obtained from the whole plant (Johnson and Sowerby, 1862; Grae, 1974).

Moreover, several medicinal uses are known for P. arenastrum. An infusion made from the twigs (including leaves and flowers) can be drank to treat back pain (Peters and Ortiz, 2010). This species is a safe diuretic herb that can be used to treat dysentery and haemorrhoids (Grieve and Leyel, 1980). As an astringent, it can be applied both internally and externally in the treatment of wounds, bleeding (Grieve and Leyel, 1980) as well as varicose veins (Chiej, 1984).

Environmental Services

A number of beneficial insects feed on the flowers of P. arenastrum (Smith et al., 2008). In addition to this Shapiro (2002) found that the butterfly Lycaena helloides, endemic to west North America, breeds almost entirely on P. arenastrum.

Uses List

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Human food and beverage

  • Flour/starch
  • Vegetable

Materials

  • Dyestuffs

Medicinal, pharmaceutical

  • Source of medicine/pharmaceutical
  • Traditional/folklore

Similarities to Other Species/Conditions

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P. arenastrum can be easily confused with P. aviculare. However, McNeil (1981) states that these species differ in flowers and fruits. P. arenastrum typically has the tepals fused for one third to one half of their length, achenes 1.4-2.5 mm long, with two convex and one much narrower, concave, side (P. aviculare sensu stricto: tepals fused for less than one third of length, achenes 2-3.5 mm long, with three concave sides). In addition, P. arenastrum usually has a more prostrate growth habit and smaller leaves, but these and other vegetative traits show extensive phenotypic plasticity in the whole aggregate. P. arenastrum most often occurs in trampled sites and is apparently much less often found as a weed of cultivated fields than P. aviculare sensu stricto (McNeill, 1981). The branch leaves of P. aviculare are half the size of the stem leaves whereas all the leaves of P. arenastrum are a similar size (Burnett and Moore, 2014).

According to Smith et al. (2008), P. argyrocoleon could also be confused with P. arenastrum. The former may be distinguished from the latter by its more erect growth habit (reaching 30 to 50 cm in height) and its long leafless, rose-colored flower spikes and its shiny seed.

It has been suggested that in Australia P. arenastrum can be confused with P. patulum. However this species has a red stem and can grow up to 800 mm in height (Burnett and Moore, 2014).

Moreover, P. arenastrum can be confused with Euphorbia maculata, E. prostrata and E. nutans, weeds of similar growing habit. These are easily distinguishable from P. arenastrum by the white exudate of the Euphorbia

Prevention and Control

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Prevention

Preventing soil compaction is one of the most important management methods for control of P. arenastrum. As stated earlier, this species thrives on compacted soils. Therefore, landscapes should be arranged so that soil is less likely to become compacted. For this purpose, Smith et al. (2008) recommend extending foot and vehicle traffic over a broader area. Moreover, they suggest the use of fences or hedges to reduce traffic, as well as the installation of rock or pavement pathways where traffic cannot be avoided. They also recommend avoiding trampling areas soon after irrigation or rainfall, as well as arranging soccer fields and athletic areas so that heavily used areas such as goals, midfields and sidelines can be rotated.

Further, Smith et al. (2008) recommend preventing seed production by controlling young plants. This will reduce the amount of seed present in the soil in succeeding years.

Control

Cultural Control and Sanitary Measures

Smith et al. (2008) propose mulching as a method of control of P. arenastrum. For this purpose, a variety of mulches can be applied to planting beds and other landscaped areas. Mulching with landscape fabrics (polypropylene or polyester fabric or black polyethylene) can be used to block plant growth. This, however, can only be effective if the fabric is overlapped and no light is allowed to penetrate to the soil (Smith et al., 2008). The use of rock or organic mulches (such as bark or compost) to top synthetic fabrics is also recommended (Smith et al., 2008). If used alone, organic mulches should be 5-10 cm thick. Finer mulch material is not desirable since seeds may easily grow in it. Coarser material will drain readily and reduce seedling establishment. Mulch needs to be replenished each year to maintain cover thickness and to eliminate light penetration to the soil. Aeration of soil may help to provide a better environment for other native plant species to grow (UCIPM, 2014).

Physical/Mechanical Control

According to Smith et al. (2008), P. arenastrum can be removed using common gardening tools. Nevertheless manual removal can be ineffective in particular when plants that grow in heavy soil break off at the base enabling them to regrow (HerbiGuide, 2015). However for control over small areas such as home gardens for example, frequent manual removal together with mulching should be sufficient to control this weed (Smith et al., 2008).

Chemical Control

Smith et al. (2008) suggest a number of pre- and post-emergent herbicides that can be employed in the control of P. arenastrum. Among the pre-emergent herbicides suitable for home use are products containing benfluralin, dithiopyr, oryzalin, pendimethalin, prodiamine and trifluralin. Postemergent herbicides like those containing dicamba (for use in turfgrass only), glyphosate and pelargonic acid will control emerged P. arenastrum. For best results, these herbicides must be used while the weed is young, preferably the early seedling stage, before it becomes more established and hardened off. Young specimens of this species (i.e., smaller than 7 cm in diameter) can be controlled with 2,4-D. Some post-emergent herbicides will only kill the top growth of a plant, making it possible for buds to regrow from the crown of the plant (Smith et al., 2008).

References

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Contributors

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01/10/2015 Original text by:

Diana Quiroz, Naturalis Biodiversity Center, The Netherlands

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