Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Amaranthus palmeri
(Palmer amaranth)

Vélez-Gavilán J, 2019. Amaranthus palmeri (Palmer amaranth). Invasive Species Compendium. Wallingford, UK: CABI. DOI:10.1079/ISC.4649.20203482869

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Datasheet

Amaranthus palmeri (Palmer amaranth)

Summary

  • Last modified
  • 14 August 2020
  • Datasheet Type(s)
  • Invasive Species
  • Host Plant
  • Preferred Scientific Name
  • Amaranthus palmeri
  • Preferred Common Name
  • Palmer amaranth
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • Amaranthus palmeri is an annual herbaceous plant that is spreading rapidly beyond its native range in North America. It is considered the most invasive species of the dioecious amaranths and is ranked as one of the most troublesome weeds...

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Pictures

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PictureTitleCaptionCopyright
Amaranthus palmeri (Palmer amaranth); habit, showing inflorescences. Delaware, USA. August 2012.
TitleHabit
CaptionAmaranthus palmeri (Palmer amaranth); habit, showing inflorescences. Delaware, USA. August 2012.
Copyright©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); habit, showing inflorescences. Delaware, USA. August 2012.
HabitAmaranthus palmeri (Palmer amaranth); habit, showing inflorescences. Delaware, USA. August 2012.©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); seeding habit. Will produce seeds at any height. It can be spread by mechanical-human use, so care should be taken to clean equipment before using sagain in a non-infested field. USA. August 2012.
TitleSeeding habit
CaptionAmaranthus palmeri (Palmer amaranth); seeding habit. Will produce seeds at any height. It can be spread by mechanical-human use, so care should be taken to clean equipment before using sagain in a non-infested field. USA. August 2012.
Copyright©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); seeding habit. Will produce seeds at any height. It can be spread by mechanical-human use, so care should be taken to clean equipment before using sagain in a non-infested field. USA. August 2012.
Seeding habitAmaranthus palmeri (Palmer amaranth); seeding habit. Will produce seeds at any height. It can be spread by mechanical-human use, so care should be taken to clean equipment before using sagain in a non-infested field. USA. August 2012.©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); habit, as an invasive in a soya bean crop. If not addressed, each plant can produce 500,000 seeds. This field contains millions of potential seeds. Delaware, USA. August 2012.
TitleHabit
CaptionAmaranthus palmeri (Palmer amaranth); habit, as an invasive in a soya bean crop. If not addressed, each plant can produce 500,000 seeds. This field contains millions of potential seeds. Delaware, USA. August 2012.
Copyright©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); habit, as an invasive in a soya bean crop. If not addressed, each plant can produce 500,000 seeds. This field contains millions of potential seeds. Delaware, USA. August 2012.
HabitAmaranthus palmeri (Palmer amaranth); habit, as an invasive in a soya bean crop. If not addressed, each plant can produce 500,000 seeds. This field contains millions of potential seeds. Delaware, USA. August 2012.©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); Leaves. USA. August 2012.
TitleLeaves
CaptionAmaranthus palmeri (Palmer amaranth); Leaves. USA. August 2012.
Copyright©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); Leaves. USA. August 2012.
LeavesAmaranthus palmeri (Palmer amaranth); Leaves. USA. August 2012.©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); habit, showing the distinctive pale-white ‘watermark’ on the leaves. Delaware, USA. August 2012.
TitleLeaves
CaptionAmaranthus palmeri (Palmer amaranth); habit, showing the distinctive pale-white ‘watermark’ on the leaves. Delaware, USA. August 2012.
Copyright©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); habit, showing the distinctive pale-white ‘watermark’ on the leaves. Delaware, USA. August 2012.
LeavesAmaranthus palmeri (Palmer amaranth); habit, showing the distinctive pale-white ‘watermark’ on the leaves. Delaware, USA. August 2012.©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); inflorescence. Las Cruces, southern New Mexico, USA. June 2006.
TitleInflorescence
CaptionAmaranthus palmeri (Palmer amaranth); inflorescence. Las Cruces, southern New Mexico, USA. June 2006.
CopyrightPublic Domain - Released by Patrick Alexander/via flickr - CC0 1.0
Amaranthus palmeri (Palmer amaranth); inflorescence. Las Cruces, southern New Mexico, USA. June 2006.
InflorescenceAmaranthus palmeri (Palmer amaranth); inflorescence. Las Cruces, southern New Mexico, USA. June 2006.Public Domain - Released by Patrick Alexander/via flickr - CC0 1.0
Amaranthus palmeri (Palmer amaranth); habit, with field worker, Mark VanGessel, for scale. Delaware, USA. August 2012.
TitleHabit
CaptionAmaranthus palmeri (Palmer amaranth); habit, with field worker, Mark VanGessel, for scale. Delaware, USA. August 2012.
Copyright©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); habit, with field worker, Mark VanGessel, for scale. Delaware, USA. August 2012.
HabitAmaranthus palmeri (Palmer amaranth); habit, with field worker, Mark VanGessel, for scale. Delaware, USA. August 2012.©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); habit, showing stems and flowers in hand. Delaware, USA. August 2012.
TitleHabit
CaptionAmaranthus palmeri (Palmer amaranth); habit, showing stems and flowers in hand. Delaware, USA. August 2012.
Copyright©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); habit, showing stems and flowers in hand. Delaware, USA. August 2012.
HabitAmaranthus palmeri (Palmer amaranth); habit, showing stems and flowers in hand. Delaware, USA. August 2012.©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); root system. Delaware, USA. August 2012.
TitleRoots
CaptionAmaranthus palmeri (Palmer amaranth); root system. Delaware, USA. August 2012.
Copyright©University of Delaware Carvel REC/via flickr - CC BY 2.0
Amaranthus palmeri (Palmer amaranth); root system. Delaware, USA. August 2012.
RootsAmaranthus palmeri (Palmer amaranth); root system. Delaware, USA. August 2012.©University of Delaware Carvel REC/via flickr - CC BY 2.0

Identity

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Preferred Scientific Name

  • Amaranthus palmeri S. Watson

Preferred Common Name

  • Palmer amaranth

Other Scientific Names

  • Amaranthus palmeri var. glomeratus Uline & W.L.Bray

International Common Names

  • English: carelessweed; dioecious amaranth; Palmer’s pigweed; pigweed
  • Spanish: quelite; quelite de aguas
  • French: amarante de Palmer
  • German: Palmer-Fuchsschwanz; Palmer-Amaranth

Local Common Names

  • Argentina: bledo
  • Mexico: quintonil tropical
  • Netherlands: tweehuizige amarant
  • Sweden: kvarnamarant

EPPO code

  • AMAPA (Amaranthus palmeri)

Summary of Invasiveness

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Amaranthus palmeri is an annual herbaceous plant that is spreading rapidly beyond its native range in North America. It is considered the most invasive species of the dioecious amaranths and is ranked as one of the most troublesome weeds of various crops in the United States. The seeds are accidentally dispersed mainly though agriculture and the crop trade. This species is reported as causing serious impacts to the growth and yield of various crops, cotton, maize, soybean and sweet potatoes being among the most affected. A. palmeri is reported as invasive in the USA, Argentina and Brazil, due to the negative impact it has on agriculture. Although the native habitat of A. palmeri is arid desert areas of the southwest USA and the north of Mexico, it is spreading fast into higher latitudes and milder climates. Its success is attributed to a combination of high fecundity, fast and season-long germination, fast initial growth, high rates of photosynthesis, phenotypic plasticity, the vast amount of seeds produced per plant (up to 600,000), the ability to produce a large biomass and the development of herbicide resistance, including to the widely used glyphosate. The range of A. palmeri is also expected to expand due to climate change that will create suitable conditions for its establishment.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Caryophyllales
  •                         Family: Amaranthaceae
  •                             Genus: Amaranthus
  •                                 Species: Amaranthus palmeri

Notes on Taxonomy and Nomenclature

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The genus Amaranthus consists of about 75 species, mostly from tropical, sub-tropical and warm temperate zones (Ward et al., 2013; Flora of North America Editorial Committee, 2019). The genus name is derived from the combination of two Greek words "amarantos," meaning "unfading, undecaying" and “anthos” for “flower” or "never failing flowers", as a description of the Amaranthus species' showy bracts (Steckel, 2007). Three subgenera are recognised: Acnida, Amaranthus, and Albersia (Flora of North America Editorial Committee, 2019). The dioecious species are included in the subgenus Acnida, all native to North America (Steckel, 2007).

Description

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The following description is from Flora of North America Editorial Committee (2019) and World Flora Online (2019):

Dioecious plants, glabrous or nearly so. Stems erect, branched, usually (0.3-)0.5-1.5(-3) m; proximal branches often ascending. Leaves: long-petiolate; blade obovate or rhombic-obovate to elliptic proximally, sometimes lanceolate distally, 1.5-7 × 1-3.5 cm, base broadly to narrowly cuneate, margins entire, plane, apex subobtuse to acute, usually with terminal mucro. Inflorescences terminal, linear spikes to panicles, usually drooping, occasionally erect, especially when young, with few axillary clusters, uninterrupted or interrupted in proximal part of plant. Bracts: of pistillate flowers with long-excurrent midrib, 4-6 mm, longer than tepals, apex acuminate or mucronulate; of staminate flowers, 4 mm, equalling or longer than outer tepals, apex long-acuminate. Pistillate flowers: tepals 1.7-3.8 mm, apex acuminate, mucronulate; style branches spreading; stigmas 2(-3). Staminate flowers: tepals 5, unequal, 2-4 mm, apex acute; inner tepals with prominent midrib excurrent as rigid spine, apex long-acuminate or mucronulate; stamens 5. Utricles tan to brown, occasionally reddish brown, obovoid to subglobose, 1.5-2 mm, shorter than tepals, at maturity walls thin, almost smooth or indistinctly rugose. Seeds dark reddish brown to brown, 1-1.2 mm diam., shiny. 

Plant Type

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Annual
Broadleaved
Herbaceous
Seed propagated
Vegetatively propagated

Distribution

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Amaranthus palmeri is an annual herb native to northwestern Mexico, the south of California into New Mexico and Texas in the United States (Ward et al., 2013). It is cited as native for all of the USA (USDA-NRCS, 2019). According to Acevedo-Rodríguez and Strong (2012), A. palmeri is native to North America and the West Indies (Cuba and Hispaniola). This reference perhaps takes into consideration the presence of the species in the Dominican Republic in 1929 (Missouri Botanical Garden, 2019); nevertheless most of the references worldwide consider the species to be native only to North America.

A. palmeri is reported in Asia, Africa, North America, the Caribbean, South America and Europe (Anastasiu et al., 2011; Acevedo-Rodríguez and Strong, 2012; De Andrade et al., 2015; Iamonico and Monki, 2017; Encyclopedia of Life, 2019; EPPO, 2019; EPPO, 2020; Euro+Med, 2019;  GRIIS, 2019; Missouri Botanical Garden, 2019; USDA-ARS, 2019).

Although some references cite the species as being present in Australia, this is probably a recording error as the only reference to A. palmeri there are three specimens from the United States deposited at the Northern Territory Herbarium (Atlas of Living Australia, 2019).

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: 12 May 2022
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes

Africa

BotswanaPresent
EgyptPresentIntroducedNaturalizedCasual alien at Sinai
EthiopiaPresentIntroduced
SenegalPresentIntroduced
South AfricaPresentIntroduced2017In cotton, maize and alfalfa fields
TunisiaPresent, Few occurrencesIntroduced2002Casual alien

Asia

ChinaPresent, Localized
IndiaPresentIntroducedNo evidence of impact
-MaharashtraPresentIntroduced
IsraelPresent
JapanPresent
-HonshuPresent
-KyushuPresent
JordanPresentIntroduced
PalestinePresentIntroduced
South KoreaPresentIntroducedNo evidence of impact
TurkeyPresentIntroducedNaturalized

Europe

AustriaPresent, Transient under eradication
BelarusAbsent, Unconfirmed presence record(s)
BelgiumPresent, Few occurrencesIntroduced1952NaturalizedCasual alien
CyprusPresent
CzechiaPresentIntroducedNo evidence of impact
DenmarkPresent, Few occurrencesIntroducedBornholm. No evidence of impact
FinlandPresent, Few occurrencesIntroducedAhvenanmaa. No evidence of impact
FranceAbsent, Formerly present
GermanyPresent, Few occurrencesIntroducedNo evidence of impact
GreecePresentIntroducedNaturalizedNo evidence of impact
ItalyPresent, Few occurrencesIntroduced
LatviaPresentIntroducedNo evidence of impact
LiechtensteinPresent, Few occurrencesIntroduced
LithuaniaPresent, Few occurrencesIntroducedNaturalizedNo evidence of impact
LuxembourgPresent, Transient under eradication
MoldovaPresent, Few occurrencesIntroduced
NetherlandsPresent, Few occurrencesIntroducedCasual alien
NorwayPresent, Few occurrencesIntroducedCasual alien
PolandPresent, Few occurrencesIntroduced
PortugalPresent
-MadeiraPresent
RomaniaPresentIntroduced1966NaturalizedAccidental introduction from shipping (no details given). Cereal trade
RussiaPresent, Few occurrencesIntroducedNo evidence of impact
SlovakiaPresentIntroducedNo evidence of impact
SpainPresentIntroduced2007NaturalizedSeen for the first time in Lleida, Cataluna at the margin of a maize field. Previously recorded at the port of Sevilla and in Palos de la Frontera (Huelva) in the vicinity of industrial premises where seeds and plant products are processed
SwedenPresent, Transient under eradication
UkrainePresentIntroducedNo evidence of impact
United KingdomPresent, Transient under eradication

North America

CanadaPresentIntroduced
-OntarioPresentInvasive
CubaPresentNative
Dominican RepublicPresentIntroduced1929La Vega. Common weed, spreading into pinelands etc
MexicoPresentNativeAguascalientes, Baja California, Baja California Sur, Chihuahua, Coahuila, Colima, Durango. Guerrero, Hidalgo, Jalisco, M?xico, Michoac?n, Morelos, Nuevo Le?n, Oaxaca, Puebla, Quer?taro, San Luis Potos?, Sinaloa, Sonora, Tamaulipas, Tlaxcala, Veracruz, Zacatecas
United StatesPresentNativeInvasiveNative to the southwest of USA from California to Texas and introduced elsewhere. Invasive weed mainly of agricultural lands
-AlabamaPresent
-ArizonaPresent
-ArkansasPresent
-CaliforniaPresent
-ColoradoPresent
-FloridaPresent
-GeorgiaPresent
-IllinoisPresent
-IndianaPresent
-IowaPresentIntroduced2016InvasiveAs a contaminant in Conservation Reserve Program seeding mixes
-KansasPresentIntroduced
-KentuckyPresent
-LouisianaPresent
-MarylandPresentIntroduced
-MassachusettsPresent
-MichiganPresent
-MinnesotaPresent
-MississippiPresent
-MissouriPresent
-NebraskaPresent
-NevadaPresent
-New JerseyPresentIntroduced
-New MexicoPresent
-New YorkPresent
-North CarolinaPresent
-North DakotaPresent
-OhioPresent
-OklahomaPresent
-PennsylvaniaPresent
-South CarolinaPresent
-South DakotaPresent
-TennesseePresent
-TexasPresent
-UtahPresent
-VirginiaPresent
-West VirginiaPresent
-WisconsinPresent

Oceania

AustraliaAbsent, Unconfirmed presence record(s)

South America

ArgentinaPresentIntroduced2011InvasiveCordoba
BrazilPresentIntroduced2014InvasiveIn fields used to cultivate cotton, soybean and corn
-Mato GrossoPresentIntroduced2014InvasiveIn fields used to cultivate cotton, soybean and corn
UruguayPresentIntroduced

History of Introduction and Spread

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Amaranthus palmeri is an annual herb native to arid and desert habitats of northern Mexico and the southwest of the USA (Ward et al., 2013). It is an opportunistic weed with the ability to outcompete other species partly due to being able to germinate throughout the season, a rapid growth rate and prolific seed production (Ehleringer, 1983). A. palmeri has spread worldwide from its native range since the early 20th century, mainly through accidental seed dispersal related to agricultural activities (Ward et al., 2013; EPPO, 2019). Other means of spread reported for the species are through water flow, including irrigation, via animals, strong winds and hurricanes (Menges,1987).

A. palmeri is believed to have arrived in Europe as a contaminant of grains and oil seed rape by the 1950s (EPPO, 2019; Alien plants of Belgium, 2019). Its arrival in South America by the first part of the 2000s is also related to crop production (De Andrade et al., 2015). Although native to areas with high temperatures and low precipitation, its phenotypic plasticity has allowed A. palmeri to spread into areas of lower temperatures and higher altitudes (Ward et al., 2013). Climate change models predict future increases in temperatures can expand the range of the species northward into portions of Canada and Europe (Kistner and Hatfield, 2018).

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Brazil 2014 Crop production (pathway cause) Yes No De Andrade et al. (2015) As a contaminant
Dominican Republic 1929 No No Missouri Botanical Garden (2019)
Argentina USA 2011 Crop production (pathway cause) Yes No Morichetti et al. (2013) As a contaminant
Romania 1966 Yes No Anastasiu et al. (2011) Accidental introduction, from shipping (no details given). Cereal trade
Spain 2007 Crop production (pathway cause) Yes No EPPO (2019) As a contaminant
Tunisia 2002 No No Iamonico and Mokni (2017)
Belgium 1952 Crop production (pathway cause) Yes No Alien plants of Belgium (2019) As a contaminant
South Africa 2017 Yes No CropLife (2019) Although means of introduction is unknown it is reported from agricultural fields

Risk of Introduction

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Amaranthus palmeri has a very high risk of unintentional introduction through crop production and trade (Ward et al., 2013). It is a successful weedy species that has become a problem of crop fields and waste lands. The resistance of some biotypes to various herbicides has been an important factor for the spread of A. palmeriis. Its range is also predicted to expand as a result of climate change (Kistner and Hatfield, 2018). Major crop producing countries with climates suitable for the establishment of A. palmeri are Australia, Nigeria, Ethiopia and Tanzania. Madagascar is also susceptible, as are countries of central and eastern Asia, the Middle East and the Caribbean.

Habitat

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Amaranthus palmeri is an annual herb native to desert and arid regions of southwestern USA and northern Mexico. It is also reported in rural areas, streambanks, disturbed areas, abandoned plots, drainage and irrigation channels, roadsides, railroads, areas used for livestock, public gardens and cultivated fields (Ward et al., 2013; Iamonico and Mokni, 2017; Encyclopedia of Life, 2019). A. palmeri can be found at altitudes of 100 to 1000 m (Encyclopedia of Life, 2019).

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial ManagedCultivated / agricultural land Present, no further details Harmful (pest or invasive)
Terrestrial ManagedCultivated / agricultural land Present, no further details Natural
Terrestrial ManagedManaged forests, plantations and orchards Present, no further details Harmful (pest or invasive)
Terrestrial ManagedManaged forests, plantations and orchards Present, no further details Natural
Terrestrial ManagedDisturbed areas Present, no further details Natural
Terrestrial ManagedRail / roadsides Present, no further details Natural
Terrestrial ManagedUrban / peri-urban areas Present, no further details Natural
Terrestrial Natural / Semi-naturalDeserts Present, no further details Natural
Terrestrial Natural / Semi-naturalArid regions Present, no further details Natural

Hosts/Species Affected

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Amaranthus palmeri is a very competitive weed found in fields of many crops, including cotton (Gossypium spp.), maize (Zea mays), soybean (Glycine max), peanut (Arachis hypogaea), sweet potato (Ipomoea batatas) and various vegetables (Ward et al., 2013). It is also reported to occur in orchards of citrus species, pecan (Carya illinoinensis), mango fruit (Mangifera indica) and apple (Malus domestica) (Mohseni-Moghadam et al., 2013; Ward et al., 2013). In the United States, A. palmeri has been ranked as one of the most troublesome weeds of various crops, especially cotton, maize and soybean (Ward et al., 2013). This species significantly affects the growth and yield of crops due to its resistance to glyphosate and other herbicides, its continual plant emergence, fast growth, prolific seed production and large biomass (Wise et al., 2009; Ward et al., 2013; Cahoon et al., 2015; EPPO, 2019). A. palmeri can also suppress the growth of crops through allelopathy (EPPO, 2019).

Host Plants and Other Plants Affected

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Growth Stages

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Flowering stage, Fruiting stage, Post-harvest, Pre-emergence, Seedling stage, Vegetative growing stage

Biology and Ecology

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Genetics

The chromosome number reported for A palmeri is n = 17 (Reveal and Spellenberg, 1976). This species can produce seeds both sexually and apomictically (Ribeiro et al., 2014). Hybridization is widely reported in the genus, but hybrids with A. palmeri have been reported to be nonviable or sterile (Steinau et al., 2003; Ward et al., 2013).

A. palmeri has high genetic diversity and is capable of developing herbicide resistance over a period of a few years (Chandi et al., 2013; Ward et al., 2013). Biotypes with glyphosate resistance are becoming more common (Ward et al., 2013). Some populations have also developed resistance to multiple herbicides. Considering that A. palmeri is originally from arid and desert habitats, its wide distribution is indicative of the phenotypic plasticity of the species (Ward et al., 2013).

Reproductive Biology

A. palmeri is an annual species with a high reproductive potential. This species is dioecious, produces vast quantities of wind-carried pollen and has prolific seed production that surpasses 600,000 seeds per plant (Ward et al., 2013; EPPO, 2019). Flowering can occur throughout the year although most of it occurs during the summer months. Although A. palmeri reproduces mainly by seed, cuttings are reported to root easily (PFAF, 2019). Seed production via apomixis has been reported by Ribeiro et al. (2014). Seeds germinate best under natural light (Ward et al., 2013). The base temperature for germination is 17°C, although germination can occur at 5-35°C (Steinmaus et al., 2000). Maximum seed germination is at temperatures near 30°C, declining with higher temperatures (Guo and Al-Khatib, 2003; EPPO, 2019). Seeds need a shallow disposition in the soil to germinate, which can occur within one to two days (Ward et al., 2013; EPPO, 2019). About 75-85% of the seeds produced each year are lost either to predation or over low temperatures during the winter. About 90% of the seeds will germinate during the next year and 10% over a four-year period (Barber et al., 2015). The seeds have been reported to be viable after 12 years of burial in the soil, although more than half of the seeds will lose viability after 18 months (EPPO, 2019).

Physiology and Phenology

A. palmeri is a C4 summer annual species that grows best in open sunny places, warm temperatures and is drought tolerant (Ehleringer, 1983; Ward et al., 2013). It is also considered an opportunistic species as seed will germinate within a day in response to intermittent rainfall, with the seedlings having a fast growth rate (Berger et al., 2015). The leaves exhibit diaheliotropic movements, which helps the species to have high photosynthetic capacity.

Although A. palmeri is not shade tolerant, the species has shown morphological acclimation to shading (Jha et al., 2008).  Light availability affects germination as plants growing in the shade produce seeds with a lower germination success than plants growing in full sun (Ward et al., 2013).

Longevity

A. palmeri is an annual species (Ward et al., 2013).

Environmental Requirements

A. palmeri can grow in almost any soil, but prefers well drained ones. It can grow in acid, neutral and basic (alkaline) soils. It will not grow well in the shade. It is drought tolerant but prefers moist soils (PFAF, 2019).

Climate

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ClimateStatusDescriptionRemark
Aw - Tropical wet and dry savanna climate Tolerated < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
BS - Steppe climate Preferred > 430mm and < 860mm annual precipitation
BW - Desert climate Preferred < 430mm annual precipitation
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)
Cf - Warm temperate climate, wet all year Tolerated Warm average temp. > 10°C, Cold average temp. > 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)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
60 41

Air Temperature

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Parameter Lower limit Upper limit
Absolute minimum temperature (ºC) 5
Mean annual temperature (ºC) 16 35

Rainfall

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ParameterLower limitUpper limitDescription
Mean annual rainfall1251400mm; lower/upper limits

Rainfall Regime

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Bimodal
Summer
Uniform
Winter

Soil Tolerances

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Soil drainage

  • free

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Lygus lineolaris Herbivore Fruits|pods; Plants|Growing point; Plants|Leaves; Plants|Seedlings; Plants|Seeds; Plants|Stems not specific N
Polymerus basalis Herbivore Fruits|pods; Plants|Growing point; Plants|Leaves; Plants|Seedlings; Plants|Seeds; Plants|Stems not specific N
Rotylenchulus reniformis Parasite Plants|Roots not specific N
Solenopsis invicta Herbivore Plants|Seeds not specific N

Notes on Natural Enemies

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Amaranthus palmeri is reported as the host of several insects including Aufeius impressicollis, Taylorilygus pallidulus [Taylorilygus apicalis], Polymerus basalis and Lygus lineolaris (Snodgrass et al., 1984; Wheeler Jr, 1988; Jones and Allen, 2012; Encyclopedia of Life, 2019). Some ant species that forage the seeds include Pheidole ridicula, P. absurda and Solenopsis invicta (Ward et al., 2013; Encyclopedia of Life, 2019). Various rodents and birds, including Charadrius vociferus and ducks, consume the seeds (Ward et al., 2013). Nematodes affecting A. palmeri include Meloidogyne incognita, M. arenaria and Rotylenchulis reniformis (Ward et al., 2013).

Means of Movement and Dispersal

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Natural Dispersal

The small seeds of A. palmeri are predominantly gravity-dispersed, but can also spread through water (Ward et al., 2013; EPPO, 2019). Although the seeds have no wind dispersal adaptations, strong winds and hurricanes are reported as dispersing the species over some areas of Texas (Menges, 1987). 

Vector Transmission (Biotic)

Small mammals, such as rodents, as well as birds are reported as seed dispersers of A. palmeri (Ward et al., 2013). The seeds retain a high percent of viability after being consumed by birds (De Vlaming and Proctor, 1968).

Accidental Introduction

A. palmeri has been reported as spreading through agricultural practices (Ward et al., 2013). The species is also reported as being dispersed through seed mixes used for habitat restoration (Murphy et al., 2017).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Animal productionManure used for livestock Yes Ward et al. (2013)
Crop productionSeeds accidentally dispersed by agricultural practices Yes Yes Ward et al. (2013)
Digestion and excretionSeeds consumed by small mammals and birds Yes EPPO (2019)
DisturbanceOften found in agricultural plots and disturbed sites Yes Ward et al. (2013)
Flooding and other natural disastersSeed dispersion by strong winds and hurricanes reported Yes Menges (1987)
Habitat restoration and improvementAccidentally dispersed by seed mixes used for habitat restoration Yes Yes Murphy et al. (2017)
HitchhikerMoved unintentionally with crop products, machinery, clothing Yes Yes Ward et al. (2013); EPPO (2019)
Interconnected waterwaysMoved via water and channels used for irrigation Yes Menges (1987); EPPO (2019)
Off-site preservation Seeds preserved at USDA-ARS facilities Yes Yes USDA-ARS (2019)
People foragingLeaves used as a vegetable and meal made from ground seed Yes Yes Ward et al. (2013)

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Bulk freight or cargoTransported accidentally with crop products Yes Ward et al. (2013)
Clothing, footwear and possessionsPossible from agriculture fields Yes Yes CropLife (2019)
Containers and packaging - woodPossible in packages used to transport crops. Yes Yes Ward et al. (2013)
Debris and waste associated with human activitiesSeeds in soil, manure and waste associated with agricultural practices Yes Ward et al. (2013)
GermplasmPreserved at USDA-ARS facilities Yes Yes USDA-ARS (2019)
Machinery and equipmentIn machinery used for crop production Yes Yes Ward et al. (2013)
Mulch, straw, baskets and sod Yes
LivestockSeeds used for cattle due to high protein content Yes Kindscher et al. (2018)
Plants or parts of plantsAs a contaminant of grains Yes Yes EPPO (2019)
Soil, sand and gravelFrom agricultural practices Yes Ward et al. (2013)
Land vehiclesFrom agricultural practices Yes Ward et al. (2013)
WaterSeeds can be dispersed by water Yes Ward et al. (2013)
WindStrong winds and hurricane dispersal of the seeds Yes Yes Menges (1987)

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
True seeds (inc. grain) weeds/seeds Yes Pest or symptoms usually visible to the naked eye

Impact Summary

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CategoryImpact
Cultural/amenity Positive and negative
Economic/livelihood Negative
Environment (generally) Positive and negative
Human health Positive and negative

Economic Impact

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Amaranthus palmeri is reported as one of the most competitive weeds of crops in the United States (Morgan et al., 2001; Norsworthy et al., 2008; Webster and Gray, 2015). Crop yield reduction is reported for soybean up to 68% with A. palmeri density of 10 plants/m of row length (Klingaman and Oliver, 1994), and for cotton of up to 92% at 0.9 plants/m2 (Rowland et al., 1999). Maize yield has been reported to be reduced 11-91% with A. palmeri densities of 0.5 to 9 plants/m row (Massinga et al., 2001). For sweet potato, crop yields have been reduced 36 to 81% at densities of 0.5 to 6.5 A. palmeri plants/m row (Meyers et al., 2010). A. palmeri also interferes with the mechanical harvest of crops (Norsworthy et al., 2008). 

Control of large infestations of A. palmeri can be very costly to landowners. For example, in Georgia, USA, cotton growers have spent more than 110 million US dollars annually in the control of A. palmeri (Webster and Gray, 2015).  A. palmeri is also an important host of the tarnished plant bug (Lygus lineolaris), which is a major pest of cotton in the United States (Steckel, 2007). 

Environmental Impact

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Impact on Habitats

There is almost no information about the impact of A. palmeri on natural habitats; the information available is on its effects over cultivated land (Peterson, 1999; Wise et al., 2009; Ward et al., 2013; Berger et al., 2015; Cahoon et al., 2015). A. palmeri outcompetes other species by a combination of various advantageous characteristics, such as resistance to glyphosate and other herbicides, high photosynthetic rate, its continued emergence and fast growth, prolific seed production, large biomass produced and the release of allelopathic compounds.

Impact on Biodiversity

The aggressiveness and rapid growth of A palmeri enable it to outcompete other species and reduce native plant diversity, which at the same time can affect wildlife and pollinators (University of Arizona Cooperative Extension, 2019).

Social Impact

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Amaranthus palmeri is reported as causing allergies (PFAF, 2019). Although this species can be used as forage it can be poisonous to livestock due to the high concentrations of nitrates present (Schmutz et al., 1974; Burrows and Tyrl, 2013). Nitrate poisoning may be lethal or sublethal, depending on levels in the plant. At sublethal levels, abortion, depression of lactation, digestive disturbances, myocardial degeneration and renal disease may occur (Kingsbury, 1964; Bryson and DeFelice, 2010). According to Burrows and Tyrl (2013), deaths are usually limited to ruminants especially cattle, with pigs tending to develop only symptoms of sublethal poisoning. Poisoning may occur when livestock graze pastures containing an abundance of Amaranthus. The presence of oxalates in A. palmeri can also be harmful to livestock (Saunders and Becker, 1984). It is therefore advisable not to graze livestock in areas predominantly infested with A. palmeri. The genus Amaranth is listed in the Cornell University list of plants poisonous to livestock with nitrate listed as the primary poison (Cornell University, 2019).

Risk and Impact Factors

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Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Has a broad native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Pioneering in disturbed areas
  • Fast growing
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
  • Reproduces asexually
  • Has high genetic variability
Impact outcomes
  • Negatively impacts agriculture
  • Negatively impacts human health
  • Negatively impacts animal health
  • Negatively impacts livelihoods
  • Reduced native biodiversity
  • Damages animal/plant products
  • Negatively impacts trade/international relations
Impact mechanisms
  • Allelopathic
  • Causes allergic responses
  • Competition - monopolizing resources
  • Hybridization
  • Poisoning
  • Pollen swamping
  • Rapid growth
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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Economic Value

There are no reports of any economic uses for A. palmeri.

Social Benefit

Amaranthus palmeri is used by indigenous populations in the United States, including the Cocopa, Navajo, Pima, Yuma and Mohave (Steckel, 2007; Ward et al., 2013). Consumption of A. palmeri seed is recommended because of its high protein and fat content (Kindscher et al., 2018). The leaves are cooked and used as a vegetable and the seeds are ground into meal for food by the Navajo and Yuma tribes (Sauer, 1957). Seeds can also be fed to cattle (Kindscher et al., 2018) although the high levels of nitrates in the adult plant can be poisonous to livestock, especially cattle and pigs (Burrows and Tyrl, 2013).

Environmental Services

No specific environmental services are reported for A. palmeri, other than seeds being consumed by animals and being used as forage (Burrows and Tyrl, 2013; Ward et al., 2013).

Uses List

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Animal feed, fodder, forage

  • Fodder/animal feed
  • Forage

Human food and beverage

  • Cereal
  • Flour/starch
  • Vegetable

Materials

  • Dyestuffs
  • Poisonous to mammals

Similarities to Other Species/Conditions

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Amaranthus palmeri is similar to A. tuberculatus, A. retroflexus and A. hybridus, all native species of North America. A. palmeri leaves sometimes have a whitish v-shaped mark on the lamina. A. retroflexus and A. hybridus have puberulous stems and leaves, while A. palmeri and A. tuberculatus have glabrous stems and leaves. The petiole of A. palmeri is longer than the leaf. The female spikes of A. palmeri are taller and pricklier than A. tuberculatus, A. retroflexus and A. hybridus (Minnesota Department of Agriculture, 2019).

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.

SPS Measures

There are several reports of the dispersal of A. palmeri to areas or countries through contaminated grains or agricultural practices (Ward et al., 2013; De Andrade et al., 2015; EPPO, 2019). Improved sanitary measures need to be implemented, including cleaning machinery to prevent seed dispersal between fields. Soil movement between fields should also be avoided. At higher spatial scales, the implementation of coordinated screening efforts at multiple stages in the feed machinery transport chains is needed to detect contamination by seeds of A. palmeri (Davis et al., 2015; EPPO, 2019). For plots where the species is detected, all equipment and machinery should be treated as if contaminated and properly sanitized (CropLife, 2019). This includes cleaning footwear and clothing. 

Early Warning Systems

Various countries are making available early warning documentation to educate the general public about the implications of an invasion of A. palmeri. These publications usually give information on how to recognise the species, how to alert the local authorities about its presence and provide instructions on the eradication means available (De Andrade et al., 2015; Barber et al., 2015). The government of Uruguay has also created a video with information about the species and a means to report its presence via the internet (Ministerio de Agricultura, Ganadería y Pesca, 2019). The use of drones to scan cultivated lands and one-kilometre radius around the farms is being recommended in South Africa to identify areas infested by A. palmeri (CropLife, 2019).

Rapid Response

A. palmeri is reported as being dispersed in seed mixes used for habitat restoration. A qPCR assay has been developed to detect the presence of this species in a mix of Amaranthus spp. seeds (Murphy et al., 2017). The implementation of scouting programmes to detect the presence of the species in agricultural land, including drainage systems, before fully reproductive is recommended. Vegetative stages should be removed completely before the plants set seed (CropLife, 2019).

Public Awareness

Central and local government agencies and institutions have published several reports to create awareness about the problems that A. palmeri presents to agriculture. The public is advised to monitor their properties, to report the presence of the species and to immediately put in place proposed measures to eliminate the species (Ward et al., 2013; Barber et al., 2015; De Andrade et al., 2015).

Eradication

The implementation of Zero Tolerance areas is recommended for the total eradication of A. palmeri (Barber et al., 2015; Crow et al., 2015; CropLife, 2019; EPPO, 2019). This should be followed up for 4-5 years to be successful. The main objective is to completely eliminate the species seedbank.

To eradicate the species, a combination of various methods, including using herbicides, manual and mechanical removal, implementing sanitary procedures, using cover crops, tillage and applying crop rotations is proposed. After harvest, agricultural plots should be inspected for the presence ofA. palmeri. Before the start of the next season, a pre-emergence herbicide should be applied to plots and adjacent fields (CropLife, 2019).

Cultural Control and Sanitary Measures

Some cultural and sanitary measures recommended for the eradication of A. palmeri include: crop rotations, alternating herbicide usage; reducing the space between the planted crops and using crop varieties with a high reproductive rate. The cleaning of vehicles and machinery before entering the plots is also recommended; setting up appropriate planting dates for crops and carefully hand weeding the existing A. palmeri plants is also suggested (EPPO, 2019).

Physical/Mechanical Control

Manual control is recommended in the absence of herbicides, when the plants have not reached the reproductive stage and before using machinery. It is important to avoid the use of machinery in areas where plants of A. palmeri are already producing seeds (EPPO, 2019). Deep tillage in autumn followed by a cover crop is also recommended as germination and seedling establishment of A. palmeri is significantly reduced when the seeds are buried at depths of 5 cm or more in the soil (EPPO, 2019). 

Chemical Control

The resistance of A. palmeri to glyphosate is a major concern for crop producers worldwide, as this herbicide is widely used for general weed control  agricultural fields (Ward et al., 2013). To control herbicide-resistant A. palmeri the rotation of herbicides having different modes of action and using a combination of multiple herbicides is recommended (Chandi et al., 2013; Ward et al., 2013; Jhala et al., 2014).

Various preemergence (PRE) and postemergence (POST) herbicides are recommended for use on A. palmeri (Ward et al., 2013; Cahoon et al., 2015; Wiggins et al., 2015). For example, for cotton fields, residual herbicides such as linuron, diuron or flumioxazin activated through precipitation or irrigation are used. For the control of emerged plants in cotton fields, glufosinate in combination with fluometuron is proposed. For infestations of maize fields, the use of glufosinate with atrazine is recommended. For soybeans, fomesafen and lactofen are used for A, palmeri plants that are less than 8 cm tall. The PRE herbicide application of combinations such as S-metolachlor + flumioxazin or flumioxazin + pyroxasulfone, followed by fomesafen is also recommended. Glufosinate is also used in soybean fields.

Recommended POST herbicide treatments include: glyphosate + S-metolachlor + mesotrione + atrazine, thiencarbazone-methyl + tembotrione + atrazine, and glyphosate + atrazine (Wiggins et al., 2015).  Dicamba is also used for the control of A. palmeri (Cahoon et al., 2015).

Gaps in Knowledge/Research Needs

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Proposed research include: the effects of light quality on growth response of A. palmeri; the effects of shading on fecundity and seed dormancy (Jha et al., 2008); mechanisms that regulate the persistence of the species in the soil seedbank (Webster and Grey, 2015); and models of potential pollen movement to help in herbicide resistance management programmes (Ward et al., 2013). More information is also needed on the effects of A. palmeri in natural habitats.

References

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Jhala, A. J., Sandell, L. D., Rana, N., Kruger, G. R., Knezevic, S. Z., 2014. Confirmation and control of triazine and 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide-resistant Palmer amaranth (Amaranthus palmeri) in Nebraska. Weed Technology, 28(1), 28-38. doi: 10.1614/WT-D-13-00090.1

Jones, G. D., Allen, K. C., 2012. Using Amaranthus palmeri pollen to mark captured tarnished plant bugs. Palynology, 36(2), 153. doi: 10.1080/01916122.2012.662178

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Wise, A. M., Grey, T. L., Prostko, E. P., Vencill, W. K., Webster, T. M., 2009. Establishing the geographical distribution and level of acetolactate synthase resistance of Palmer amaranth (Amaranthus palmeri) accessions in Georgia. Weed Technology, 23(2), 214-220. doi: 10.1614/WT-08-098.1

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Distribution References

Acevedo-Rodríguez P, Strong M T, 2012. Catalogue of the Seed Plants of the West Indies. Washington, DC, USA: Smithsonian Institution. 1192 pp. http://botany.si.edu/Antilles/WestIndies/catalog.htm

Ali A, Abdalla O, Bruton B, Fish W, Sikora E, Zhang S, Taylor M, 2012. Occurrence of viruses infecting watermelon, other cucurbits, and weeds in the parts of Southern United States. Plant Health Progress. PHP-2012-0824-01-RS. http://www.plantmanagementnetwork.org/php/elements/sum.aspx?id=10469&photo=5779

Alien plants of Belgium, 2019. Manual of the alien plants of Belgium. In: Manual of the alien plants of Belgium. Belgium: National Botanic Garden of Belgium. http://alienplantsbelgium.be/

Anastasiu P, Negrean G, Samoilǎ C, Memedemin D, Cogǎlniceanu D, 2011. A comparative analysis of alien plant species along the Romanian Black Sea coastal area. The role of harbours. Journal of Coastal Conservation. 15 (4), 595-606.

CropLife, 2019. Plan for eradication of the Palmer amaranth (Amaranthus palmeri) in the Republic of South Africa., Centurion, South Africa: CropLife. 17 pp. https://www.grainsa.co.za/upload/Plan-for-eradication-of-the-Palmer-Amaranth-in-SA.pdf

De Andrade Jr ER , Cavenaghi AL, Guimarães SC, 2015. Circular Técnica, Rondonópolis, Brazil: Instituto Mato-grossense do Algodão (IMAmt). 8 pp.

Encyclopedia of Life, 2019. Encyclopedia of Life. In: Encyclopedia of Life. http://www.eol.org

EPPO, 2019. EPPO Global database. In: EPPO Global database. Paris, France: EPPO. https://gd.eppo.int/

EPPO, 2022. EPPO Global database. In: EPPO Global database, Paris, France: EPPO. 1 pp. https://gd.eppo.int/

Euro+Med, 2019. Euro+Med PlantBase - the information resource for Euro-Mediterranean plant diversity. In: Euro+Med PlantBase - the information resource for Euro-Mediterranean plant diversity. http://ww2.bgbm.org/EuroPlusMed

GRIIS, 2019. Global Register of Introduced and Invasive Species., http://www.griis.org/

Iamonico D, El-Mokni R, 2017. Amaranthus palmeri, a second record for Africa and notes on A. sonoriensis nom. nov. Bothalia - African Biodiversity & Conservation. 47 (1), Art.#2100. DOI:10.4102/abc.v47i1.2100

Kistner E J, Hatfield J L, 2018. Potential geographic distribution of Palmer amaranth under current and future climates. Agricultural and Environmental Letters. 3 (1), 170044. DOI:10.2134/ael2017.12.0044

Missouri Botanical Garden, 2019. Tropicos database. In: Tropicos database. St. Louis, Missouri, USA: Missouri Botanical Garden. http://www.tropicos.org/

Murphy B P, Plewa D E, Phillippi E, Bissonnette S M, Tranel P J, 2017. A quantitative assay for Amaranthus palmeri identification. Pest Management Science. 73 (11), 2221-2224. DOI:10.1002/ps.4632

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. http://www.nature.com/articles/ncomms14435

USDA-ARS, 2019. Germplasm Resources Information Network (GRIN). Online Database. In: Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysimple.aspx

USDA-NRCS, 2019. The PLANTS Database. In: The PLANTS Database. Greensboro, North Carolina, USA: National Plant Data Team. https://plants.sc.egov.usda.gov

Contributors

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08/09/2019 Original text by:

Jeanine Vélez-Gavilán,  University of Puerto Rico at Mayagüez, Puerto Rico

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