Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Trapa natans
(waterchestnut)

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Datasheet

Trapa natans (waterchestnut)

Summary

  • Last modified
  • 08 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Trapa natans
  • Preferred Common Name
  • waterchestnut
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • T. natans is a productive, annual, floating-leaved plant which has been cultivated globally for the nutritious nut it produces (

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Pictures

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PictureTitleCaptionCopyright
Farmer harvesting his crop of T. natans in India.
TitleWater chestnut crop being harvested
CaptionFarmer harvesting his crop of T. natans in India.
Copyright©Chris Parker/Bristol, UK
Farmer harvesting his crop of T. natans in India.
Water chestnut crop being harvestedFarmer harvesting his crop of T. natans in India.©Chris Parker/Bristol, UK
Trapa natans plants with fruit being indicated by observer in India.
TitlePlants in hand
CaptionTrapa natans plants with fruit being indicated by observer in India.
Copyright©Chris Parker/Bristol, UK
Trapa natans plants with fruit being indicated by observer in India.
Plants in handTrapa natans plants with fruit being indicated by observer in India.©Chris Parker/Bristol, UK

Identity

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Preferred Scientific Name

  • Trapa natans L. (1753)

Preferred Common Name

  • waterchestnut

Other Scientific Names

  • Trapa natans var. quadrispinosa Makino (1820)
  • Trapa quadrispinosa Roxb. (1820)

International Common Names

  • English: watercaltrop
  • Spanish: castagna de agua
  • French: noix aquatique

Local Common Names

  • Germany: Wassernuss
  • Italy: castana d'acqua; tribolo acquatico
  • Netherlands: waternoot
  • Sweden: vattennoet

EPPO code

  • TRPNA (Trapa natans)

Summary of Invasiveness

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T. natans is a productive, annual, floating-leaved plant which has been cultivated globally for the nutritious nut it produces (Hummel and Kiviat, 2004). It is an extremely important food crop in China and India and is protected in Europe (Hummel and Kiviat, 2004), but in its introduced range, it grows in thick stands that displace native vegetation and affect water quality. Thick beds of water chestnut can cause significant declines in dissolved oxygen that negatively affect sensitive fauna (Hummel and Findlay, 2006). The nearly impenetrable mats are of virtually no use to wildlife and interfere with boating, fishing and swimming, while the large, spiny nuts can cause injuries to swimmers (ISSG, 2005). T. natans sets abundant seed, making it difficult to eradicate once it is introduced (Les and Mehrhoff, 1999).

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Myrtales
  •                         Family: Trapaceae
  •                             Genus: Trapa
  •                                 Species: Trapa natans

Notes on Taxonomy and Nomenclature

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The genus Trapa L. has been reported as having extremely confusing morphology worldwide; it has previously been classified as one polymorphic group or as one genus having up to around 20 different species (Takano and Kadono, 2005). The genus Trapa is presently placed in the monogeneric family Trapaceae (Missouri Botanical Garden, 2010), otherwise sometimes in the family Lythraceae (USDA-ARS, 2008), though it has also been placed in Hydrocaryaceae (Hummel and Kiviat, 2004) or in the family Onagraceae (Hsuan Keng, 1978). Most botanists recognize two species in the Trapa genus: T. bicornis and T. natans. T. natans is an important food crop; many regional varieties are grown in different parts of the world. Official accounts recognize two: T. natans var. natans L. and var. bispinosa (ITIS, 2007). In general, European lines are early flowering, but have lower yield, Asian lines have higher rosette densities and small fruits, while the Chinese and Indian lines have higher yields due to their large fruits (Lalith et al., 2007; Pshennikova, 2007).


           

Description

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T. natans is an herbaceous, floating-leaf aquatic species that often grows in water around 60 cm deep (PFAF, 2000). The floating leaves are arranged in a rosette, with leathery upper leaves up to 5 cm wide and broadly rhomboid, triangular, deltoid or broadly ovate (Hummel and Kiviat, 2004). The leaves are sharply serrate, with conspicuous venation and short, stiff hairs. The species also produces submersed leaves that are strikingly morphologically different (Bitonti et al., 1996). The submersed leaves are alternate, finely divided, and can grow up to 15 cm long (Mehrhoff et al., 2003). The petioles of the floating leaves have a spongy floating section that allows for the flotation of the leaf rosette, and each stem may produce several rosettes (Hummel and Kiviat, 2004). The plant also has white flowers with four 8 mm-long petals and four green sepals. The fruit is a single-seeded horned nut-like structure, sometimes referred to as a "turbinate drupe" that develops underwater and is approximately 3 cm wide (Mehrhoff et al., 2003). Single flowers are produced in axils of floating leaves (Hummel and Kiviat, 2004). The stem of the plant is flexible, from 1 to 5 m long, nodes of the stem have slender linear roots, while the plant is anchored in the sediment by the lower roots that emerged from the propagating seed hull (Hummel and Kiviat, 2004).

Plant Type

Top of page Annual
Broadleaved
Herbaceous
Seed propagated
Vegetatively propagated

Distribution

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The genus Trapa is cultivated worldwide for the harvest of its large, nutritious nut. It currently occupies a wide yet discontinuous native range across Europe, Asia, and Africa, and has been introduced to North America and Australia. It was more widespread in Tertiary times than it is currently (Ithaka Harbors Inc, 2008). The variety T. natans var. natans, with its four-spined nutis widely distributed in Eurasia, Africa and the northeastern United States, whereas T. natans var. bispinosa (also known as T. bicornis, T. bicornuta, or T. japonica) a two-spined variety, grows in China, Japan, India and Southeast Asia (Hummel and Kiviat, 2004). It is preferentially associated with low-energy, high-nutrient systems (USDA-NRCS, 2008).

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

BangladeshPresentNativeThe Bayscience Foundation, 2008
ChinaUnconfirmed recordCAB Abstracts; GBIF, 2008
-FujianPresentNativeThe Bayscience Foundation, 2008
-GuangdongPresentNativeThe Bayscience Foundation, 2008
-GuizhouPresentNativeThe Bayscience Foundation, 2008
-HainanPresentNativeThe Bayscience Foundation, 2008
-HubeiPresentNativeThe Bayscience Foundation, 2008
-HunanPresentNativeThe Bayscience Foundation, 2008
-SichuanPresentNativeThe Bayscience Foundation, 2008
-TibetPresentNativeThe Bayscience Foundation, 2008
-XinjiangPresentNativeThe Bayscience Foundation, 2008
-YunnanPresentNativeThe Bayscience Foundation, 2008
Georgia (Republic of)PresentNative Not invasive ISSG, 2007
IndiaPresentNative Invasive ISSG, 2007Northwest India
IndonesiaPresentNativeThe Bayscience Foundation, 2008
JapanPresentNative Invasive ISSG, 2007
LaosThe Bayscience Foundation, 2008
PakistanPresentNative Not invasive ISSG, 2007
PhilippinesPresentNativeThe Bayscience Foundation, 2008
TaiwanPresentGBIF, 2008
ThailandPresentGBIF, 2008
TurkeyPresentNative Not invasive ISSG, 2007Present in Northwest Turkey
VietnamPresentNative Not invasive ISSG, 2007

Africa

AlgeriaPresentNative Not invasive ISSG, 2007
AngolaPresentNative Not invasive ISSG, 2007
BotswanaPresentNative Not invasive ISSG, 2007
Burkina FasoPresentIntroduced Invasive ISSG, IUCN SSC Invasive Species Specialist Group; GBIF, 2008
Guinea-BissauPresentNative Not invasive ISSG, 2007Present in Cacheu
MalawiPresentNative Not invasive ISSG, 2007
MozambiquePresentNative Not invasive ISSG, 2007
NamibiaPresentNative Not invasive ISSG, 2007
NigerThe Bayscience Foundation, 2008
NigeriaPresentGBIF, 2008
South AfricaPresentNative Not invasive ISSG, 2007Present in Natal
TanzaniaPresentNative Not invasive ISSG, 2007
TunisiaPresentNative Not invasive ISSG, 2007
UgandaPresentNative Not invasive ISSG, 2007
ZambiaPresentNative Not invasive ISSG, 2007
ZimbabwePresentNative Not invasive ISSG, 2007

North America

CanadaPresentPresent based on regional distribution.
-QuebecPresentIntroduced Invasive O'Neill, 2006
USAPresent
-ConnecticutPresentIntroduced1999 Invasive O'Neill, 2006
-DelawarePresentIntroduced Invasive USDA-NRCS, 2008
-MarylandPresentIntroduced Invasive O'Neill, 2006
-MassachusettsPresentO'Neill, 2006
-New JerseyPresentIntroduced Invasive USDA-NRCS, 2008
-New YorkUnconfirmed recordCAB Abstracts; O'Neill, 2006
-PennsylvaniaPresentIntroduced Invasive O'Neill, 2006
-VermontPresentIntroduced Invasive O'Neill, 2006
-VirginiaEradicatedIntroduced Invasive ISSG, 2007

Europe

AlbaniaPresentNative Not invasive ISSG, 2007
AustriaPresentNative Not invasive ISSG, 2007
BelarusPresentNative Not invasive ISSG, 2007
BelgiumPresentISSG, 2007
Bosnia-HercegovinaPresentNative Not invasive ISSG, 2007
BulgariaPresentNative Not invasive ISSG, 2007
Czech RepublicPresentNative Not invasive ISSG, 2007
DenmarkPresentGBIF, 2008
FinlandPresentGBIF, 2008
FrancePresentNative Not invasive ISSG, 2007
GermanyPresentNative Not invasive ISSG, 2007
GreecePresentNative Not invasive ISSG, 2007
HungaryPresentNative Not invasive ISSG, 2007
ItalyUnconfirmed recordCAB Abstracts; ISSG, 2007
LatviaPresentNativeGBIF, 2008
NetherlandsPresentGBIF, 2008
PolandPresentISSG, 2007
RomaniaPresentNative Not invasive ISSG, 2007
Russian FederationPresentNativeThe Bayscience Foundation, 2008
SwedenPresentGBIF, 2008
SwitzerlandPresentNative Not invasive ISSG, 2007
UkrainePresentNative Not invasive ISSG, 2007

Oceania

AustraliaPresentIntroducedISSG, 2007

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Connecticut 1999
Massachusetts Europe 1879 Aquaculture (pathway cause) ,
Botanical gardens and zoos (pathway cause)
Les and Mehrhoff (1999)
New York 1884 Aquaculture (pathway cause) ,
Botanical gardens and zoos (pathway cause)
Vermont 1940s Hitchhiker (pathway cause)Les and Mehrhoff (1999)

Risk of Introduction

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T. natans has largely been spread as a result of intentional plantings. There have been many reports of escape from cultivation, and the species was originally introduced as an ornamental (Les and Mehrhoff, 1999). T. natans remains well-established in the North Eastern United States to this day (Hummel and Kiviat, 2004). The plant annually produces nuts that sink to the sediment and germinate. The rough spines of the fruit make it generally unpalatable to wildlife, reducing the likelihood of the species being spread this way. Instead, seeds disperse passively, being carried by water currents as they drop to the sediment surface (Boylen et al., 2006). The spines of the fruit also allow it to spread over longer distances as a hitchhiker, when it clings to boats and gear (Hummel and Kiviat, 2004).

Habitat

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T. natans is found world-wide in full sun and low-energy, nutrient-rich fresh waters (Hummel and Kiviat, 2004). It is commonly found in waters with alkalinity ranging from 12 to 128 mg/L of calcium carbonate (O’Neill, 2006), and dislikes calcium-rich waters (PFAF, 2000). Mixed reports exist on the depths of water typically inhabited by T. natans. Some sources report the plant can grow in water up to 5 m deep (Pemberton, 2002), others report that T. natans can be found in depths ranging from 0.3 to 3.6 m (Hummel and Kiviat, 2004), whereas others report a maximum depth of 0.6 m (PFAF, 2000). Hummel and Kiviat (2004) report that the species is found most abundantly in water around 2 m deep and in soft substrate. It also prefers slightly acidic water (PFAF, 2000), although germination can occur in water with pH ranging from 4.2 to 8.3 (Hummel and Kiviat, 2004). The species is disturbance-tolerant; it has been shown that sewage inputs create favourable conditions of increased alkalinity for the plant, and that increased nitrogen is correlated with increased petiole and fruit biomass. T. natans does not tolerate salinity; its seeds will not germinate when NaCl concentrations exceed 0.1% (Hummel and Kiviat, 2004).

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial
Freshwater
 
Irrigation channels Present, no further details Harmful (pest or invasive)
Irrigation channels Present, no further details Productive/non-natural
Lakes Principal habitat Harmful (pest or invasive)
Lakes Principal habitat Productive/non-natural
Reservoirs Principal habitat Harmful (pest or invasive)
Reservoirs Principal habitat Productive/non-natural
Rivers / streams Principal habitat Harmful (pest or invasive)
Rivers / streams Principal habitat Productive/non-natural
Ponds Principal habitat Harmful (pest or invasive)
Ponds Principal habitat Productive/non-natural

Hosts/Species Affected

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Where conditions are favourable, T. natans can cover almost 100% of the water surface and shade up to 95% of sunlight (Hummel and Kiviat, 2004). Thus, the effects of the species on native vegetation in its adventive range are significant. Water chestnut is considered an invasive, destructive species, and has been implicated in the loss of many other plant and animal species. In the Hudson River, for instance, the plant has replaced water celery (Vallisneria americana ), clasping pondweed (Potamogeton perfoliatus .) nonindigenous Eurasian watermilfoil (Myriophyllum spicatum .). However, the shelter created by the rosettes is beneficial for duckweeds (Lemna minor , Spirodela polyrhiza. and Wolffia spp.) and filamentous algae. Other emergent species that grow above the waterline, including cattail (Typha angustifolia ), pickerelweed (Pontederia cordata), and spatterdock (Nuphar advena ) are unaffected by the presence of T. natans (Hummel and Kiviat, 2004).

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Myriophyllum spicatum (spiked watermilfoil)HaloragidaceaeWild host
Potamogeton perfoliatusPotamogetonaceaeWild host
Vallisneria americana (Vallisneria)HydrocharitaceaeWild host

Growth Stages

Top of page Flowering stage, Fruiting stage, Pre-emergence, Seedling stage, Vegetative growing stage

Biology and Ecology

Top of page Genetics 

The taxonomy of the genus Trapa is confusing, it has been varyingly considered as part of one polymorphic group, or as a genus with approximately 20 species. Enzyme electrophoresis indicates, for example, three distinct lineages in the Japanese Trapa. The analysis indicates that two varieties of Trapa have different chromosome numbers (2n = 96 and 2n = 48). However, the authors recognize that despite the distinct genetic differences, the species T. natans and T. bispinosa may be a polymorphism of the same single species (Takano and Kadono, 2005). A different study identified genotypic variation as an important factor affecting organogenesis in more than 18 different T. natans genotypes drawn from all over the world (Aminul Hoque et al., 2007). However, the current tendency is to consider the family Trapaceae as a single monogeneric group containing two species that exhibit high genetic and morphological variation. Missouri Botanical Garden (2010) refers to a study showing chromosome numbers of 44, 46, 48, 90 and 96-97).

 
Reproductive Biology
 

T. natans is an annual species that produces single, bisexual flowers on stalks produced from the centre of the floating rosettes. The flower has a two-chambered ovary, four stamens, four petals, and four sepals that eventually become the spines of the fruit (GBIF, 2008). The flowers are generally pollinated by insects, but self-pollination may occur before the flower opens (Hummel and Kiviat, 2004). Once fertilized, the flower stalks droop downward, allowing the ovary to develop underwater into a nut-like barbed fruit (GBIF, 2008). The seed has two unequal cotyledons, one of which is large and starchy. Each seed produces 10 to 15 rosettes, and each rosette can give rise to up to 20 seeds (O’Neill, 2006). Seeds can remain dormant in the sediments for up to 10 years but do not tolerate dessication (Hummel and Kiviat, 2004). Vegetative reproduction is also very important to the growth and spread of the plant. The plant produces ramets that can break off and move away from the rest of the clone and survive to produce seeds. This attribute allows for extremely rapid clonal expansion, for example, a 10-fold increase was documented in 1 year in Lake Champlain (Groth et al., 1996). In fact, it has been suggested that this annual plant might act as a perennial in parts of its exotic range, mainly through rapid proliferation from clonal fragments year to year (Groth et al., 1996).

Physiology and Phenology


In spring (May in the Northeastern USA), stems bearing leaf rosettes elongate toward the surface of the water. The rosettes flourish and remain green until autumn. The plant begins to flower in early summer, and can continue to flower through to autumn (June to September in its North American range). The fruits mature mid-summer through autumn, after which they sink to the sediment when the plant begins to senesce. The plant quickly decomposes, but the seeds can stay dormant for up to 10 years. The nut overwinters in the sediment, but when water temperature rises to 12 ºC, the terminal pore begins to rot, and around 1 month later, the seed germinates (Hummel and Kiviat, 2004).

 
Associations
 

T. natans is an extremely widespread species and its worldwide distribution means it has a great many associates.

 
Environmental Requirements
 

In its alien range, T. natans can grow in any freshwater setting (Swearingen et al., 2002) and is found typically in water from 0.3 to 3.6 m deep (Hummel and Kiviat, 2004). It is restricted to low-energy systems and favours nutrient-rich waters with pH from 6.7 to 8.2 and alkalinity from 12 to 128 mg/L calcium carbonate (O’Neill, 2006).

 

Climate

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ClimateStatusDescriptionRemark
A - Tropical/Megathermal climate Tolerated Average temp. of coolest month > 18°C, > 1500mm precipitation annually
Am - Tropical monsoon climate Tolerated Tropical monsoon climate ( < 60mm precipitation driest month but > (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])
B - Dry (arid and semi-arid) Tolerated < 860mm precipitation annually
C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
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 Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
D - Continental/Microthermal climate Tolerated Continental/Microthermal climate (Average temp. of coldest month < 0°C, mean warmest month > 10°C)
Ds - Continental climate with dry summer Tolerated Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)

Soil Tolerances

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Soil drainage

  • seasonally waterlogged

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Aix sponsa Herbivore
Anser fabalis Herbivore
Athelia rolfsii Pathogen Whole plant not specific
Bagous Herbivore
Bagous rufimanus Herbivore Fruits/pods/Stems not specific
Bagous tersus Herbivore Leaves
Bagous trapae Herbivore Stems
Bagous vicinus Herbivore
Bipolaris tetramera Pathogen Leaves
Botryotinia fuckeliana Pathogen Whole plant not specific
Castor canadensis Herbivore Fruits/pods/Leaves
Cercospora Pathogen Leaves not specific
Chironomus Herbivore Leaves
Galerucella birmanica Herbivore Leaves
Galerucella nymphaeae Herbivore Leaves not specific
Galerucella singhara Herbivore Leaves
Lymnaea auricularia Herbivore Leaves not specific
Macrosteles purpurata Herbivore Leaves not specific
Nanophyes Herbivore Leaves
Nanophyes japonica Herbivore Leaves
Nanophyes rufipes Herbivore
Nymphula Herbivore Leaves
Nymphula crisonalis Herbivore Leaves
Nymphula gangeticalis Herbivore Leaves
Nymphula interruptalis Herbivore Inflorescence/Leaves not specific
Nymphula responsalis Herbivore Inflorescence/Leaves not specific
Odocoileus virginianus Herbivore Leaves
Ondatra zibethicus Herbivore
Parapoynx vittalis Herbivore Leaves not specific
Rattus norvegicus Herbivore
Rhopalosiphum nymphaeae Herbivore Leaves not specific
Sciurus carolinensis Herbivore Fruits/pods/Leaves
Sclerotium hydrophilum Pathogen Leaves
Spodoptera litura Herbivore Leaves not specific
Tamias striatus Herbivore
Tamiasciurus hudsonicus Herbivore

Notes on Natural Enemies

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Many natural enemies in the native range of T. natans have been documented by Pemberton (1999). The plant is native to the Old World, and many enemies (insects, fungi, viruses) are found throughout its native range. Of the currently explored enemies, he reports that the most common and damaging species in Asia is the weevil Galerucella birmanica which causes complete defoliation of entire populations and is also somewhat host-specific (oligophagous). Hummel and Kiviat (2004) report observations on natural enemies in the plant’s alien range. T. natans is productive and is occasionally a nuisance in its native range, therefore, natural enemies are extremely important to keep populations in check. A major reason behind why the plant is so problematic in its introduced range is precisely because of release from predation (O’Neill, 2006).

Means of Movement and Dispersal

Top of page Natural Dispersal
 

T. natans disperses primarily through water flow. The nuts are 20% heavier than the surrounding water, and as the nuts sink downward, water currents carry them a short distance away from the parent plant. Additionally, when ramets break, groups of rosettes can detach from the clone and float a long distance to establish a new population much further away from the parent plant (Hummel and Kiviat, 2004).

 
Vector Transmission
 

Humans may be the primary vector of transmission. T. natans has been historically valued as an ornamental; its escape from ornamental and botanical gardens that probably explains the invasion of the plant in the New World (Les and Mehrhoff, 1999). Although still available from online distributors, current educational efforts aim to decrease the probability that this plant will be intentionally introduced, and hopefully cut down on accidental release in areas where this plant has been declared a noxious weed. Les and Mehrhoff (1999) report observations of nuts attached to the feathers of geese, although they hypothesize that due to the size and weight of the nuts (6 g), it is unlikely that they would remain attached during prolonged flight, so although waterfowl may be a possible vector of transmission, dispersal in this manner probably only occurs over short distances.

 
Accidental Introduction
 

Humans can serve as a transmissive vector: the nuts have spines that allow the seed to move as a hitchhiker on boats and attached equipment (Les and Mehrhoff, 1999). This factor has contributed to the spread of T. natans in its alien range from the Hudson River to Lake Champlain via interconnected waterways (Les and Mehrhoff, 1999).

 
Intentional Introduction
 

T. natans was intentionally introduced into its alien range around the end of the nineteenth century (Les and Mehrhoff, 1999). The species remains an attractive water garden plant as well as a valuable food crop, and it is possible that intentional introduction will help expand this species’ range further.

 

Impact Summary

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

Economic Impact

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T. natans is an economic asset in its native range as it is an important food crop and a staple in many areas. However, in its introduced range, the plant is a significant nuisance. The economic cost of T. natans in the northeastern United States is not well documented (Pemberton, 2002), but we do know that from 1982 to 2001, $4.3 million dollars were spent on the control of T. natans in the Lake Champlain basin alone (Naylor, 2003). The largest control program, which takes place in Vermont, USA, was estimated to cost $500,000 in the year 2000 (Pemberton, 2002).

Environmental Impact

Top of page Impact on Habitat
 

T. natans can have severe impacts on the environment. When compared to areas vegetated by native species, areas under T. natans beds experienced higher variation in (varying) dissolved oxygen (DO) levels. In a study on the Hudson River, dangerously low DO values (below 5 mg/L) occurred 51% of the time, and levels below 2.5 mg/L occurred 30% of the time, while DO below 5 mg/L never occurred in native Vallisneria beds (Caraco and Cole, 2002). These observed low levels can be lethal to fish, and consequently cause the migration of small fish from under the canopy to the edges of the beds, which in turn can cause the congregation of game fish at the edges of the beds (O’Neill, 2006).

 

Where the plant is very abundant, up to 50 rosettes can grow within 1 square metre, covering the water with up to three layers of leaves (Pemberton, 2002). The high density growth of which T. natans is capable can result in a decrease in light penetration. In one study that occurred in the Hudson River, only 0.5% of incident light reached a depth of 0.2 metres underneath large beds of T. natans (Caraco and Cole, 2002). Yet other studies report the species’ general ability to intercept 95% of incident light (Hummel and Kiviat, 2004).

 
Impact on Biodiversity
 

Due to the species’ ability to shade out other submersed vegetation, it is generally considered a threat to biodiversity in its introduced range. The species also has an effect on epiphyton communities. In its native range, epiphyton development was shown to be significantly higher on submerged plants than on T. natans, while taxonomic composition of epiphytic algae, but not macroinvertebrates, was higher on T. natans (Cattaneo et al., 1998).

 

Social Impact

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This plant can cause substantial nuisance to recreational users by impeding navigation and tangling fishing line. This species has little nutritional benefit for fish or waterfowl, and can have detrimental effect on native game species that utilize the area. Additionally, the sharp spines present on the nuts can result in puncture wounds to swimmers (O’Neill, 2006). The plant may have played a role in the drowning deaths of a woman and two children in 2001 on the Hudson River (Hummel and Kiviat, 2004). Some people eat the chestnuts raw and ingest the giant intestinal fluke Fasciolopsis buski that is known to cause fasciolopsiasis, and the beds are known to be good breeding grounds for mosquitoes (Hummel and Kiviat, 2004). However, there is evidence that the T. natans nuts have been consumed by humans as early as 8000 BC. Currently the nut is valued worldwide for both its nutritional value as well as its medicinal properties.

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Benefits from human association (i.e. it is a human commensal)
  • 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
  • Altered trophic level
  • Conflict
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Increases vulnerability to invasions
  • Modification of natural benthic communities
  • Modification of nutrient regime
  • Monoculture formation
  • Negatively impacts cultural/traditional practices
  • Negatively impacts livelihoods
  • Negatively impacts aquaculture/fisheries
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
  • Transportation disruption
Impact mechanisms
  • Competition - monopolizing resources
  • Competition - shading
  • Competition - smothering
  • Competition
  • Rapid growth
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately
  • Difficult/costly to control

Uses

Top of page Economic Value

T. natans
has long been consumed by humans across the globe (Hummel and Kiviat, 2004). The nuts have a high moisture content and are valued for quenching thirst as well as being used as a source of flour that forms the base for many different food products (Hummel and Kiviat, 2004). Nuts are composed of 15% protein, 7.5% fat, 52% starch, 3% sugar and 22.5% water (Hummel and Kiviat, 2004). Singhara nut plants (related subspecies) are highly productive and are capable of high yields (typically 260-370 g/m2 and up to 550 g/m2) (Hummel and Kiviat, 2004). As well as being an important food source, the nut has also been recommended for use as paper pulp, fertilizer, fish food, compost and biofuel (Hummel and Kiviat, 2004).

 
Social Benefit
 

The plant is used medicinally to treat rabies, poisonous animal bites, diarrhea, amoebic dysentery and other complications (Hummel and Kiviat, 2004).T. natans has also been used in a herbal mixture that has proven to provide relief from the symptoms associated with recurrent herpes genitalis and labialis (Hijikata et al., 2007).The rind of the fruit has been discovered to have antibacterial activity, and is primarily effective against gram negative bacteria (Parekh and Chanda, 2007).

Environmental Services

 

While being widely reported as productive, and as a nuisance in its invasive range, T. natans is capable of some environmental services. The plant is able to fix a large quantity of nitrogen and phosphorus (Marion and Paillisson, 2003). This attribute conveys a certain amount of potential for the plant to be used as a tool to reduce eutrophication, however, the vegetation must be removed annually prior to its decay and subsequent release of sequestered nutrients (Hummell and Kiviat, 2004). Water chestnut may also be used in environmental reclamation, as it is capable of accumulating heavy metals, although not at levels as high as other species commonly used in this capacity (Hummel and Kiviat, 2004).

 

Uses List

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Animal feed, fodder, forage

  • Fishmeal

Environmental

  • Landscape improvement
  • Revegetation
  • Wildlife habitat

Fuels

  • Biofuels

General

  • Botanical garden/zoo
  • Ritual uses
  • Sociocultural value

Human food and beverage

  • Flour/starch
  • Nuts
  • Sugar

Materials

  • Chemicals
  • Essential oils
  • Fertilizer
  • Fibre

Medicinal, pharmaceutical

  • Source of medicine/pharmaceutical
  • Traditional/folklore

Detection and Inspection

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The distinct floating rosette makes this aquatic species easier than most to detect soon after invasion. 

Similarities to Other Species/Conditions

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T. natans is unlikely to be readily confused with native plants in its adventive range. The distinctive floating rosette of leathery green leaves and the production of large horned nuts means it is highly morphologically distinct from other floating-leaf species. The two most commonly recognized varieties are distinguished based on the number of spines. The Eurasian/European varieties always have four spines, whereas the Asian varieties (Trapa natans var. bispinosa) have two spines.

Prevention and Control

Top of page Prevention 

Since T. natans remains valued for its nutritional and cultural uses, and since it is still a plant of botanical interest, educational programs must be directed to educate the public about the dangers this plant poses outside of its native range. Teaching users how to clean equipment in a way that decreases the chance of transmission is one way to lessen the impact of human-mediated transport. Several of the United States have legislated the regulation of the purchase, transportation, and introduction of this species.

Rapid response 

It is much easier and more effective to attempt to control this plant early in its introduction timeline. Small populations are effectively controlled by hand pulling, preferably prior to the production of the propagating nuts. If the infestation is allowed to persist, it will probably grow quickly. It has been reported that this species is capable of increasing its biomass by ten times in a single year (Groth et al., 1996). Large infestations must be controlled by mechanical harvesters or herbicides and can be quite costly (O’Neill, 2006). 

Public awareness

Numerous educational campaigns have been directed at informing the public about the danger of aquatic invasive species in states of the USA in which T. natans is particularly problematic commonly distribute informational materials about its identity as well as instructions on how to report new invasions. Other educational campaigns have been directed toward informing the public about how to clean equipment in order to prevent the movement of invasive species.

Eradication

It has been reported that this species was eradicated from the state of Virginia, USA (ISSG, 2007).

Control

Cultural control and sanitary measures 


Nuts, though large and not as portable as propagules of other aquatic invasive species can remain dormant for up to 10 years, so it is extremely important to decrease the instances of accidental introduction by addressing humans as vectors. Additionally, since the plant is capable of producing ramets and engaging in vegetative clonal expansion via plant fragments, establishing guidelines on how to properly clean equipment, dispose of water, and identify target plants will probably decrease instances of accidental transportation and release.

Physical/mechanical control

Since the seeds of T. natans can remain dormant for up to 10 years, annual control efforts for at least that long must be undertaken in order for there to be a chance of eradication (O’Neill, 2006). Large beds must be mechanically harvested, but this will provide relief for only one growing season (O’Neill, 2006). Smaller areas of infestation can be addressed with hand pulling, although care must be exercised that all parts of the plant be removed, lest fragments remain to mature and produce fruits (Hummel and Kiviat, 2004). Ultrasound has also been proposed as a possible method of control. After treatment of the stem with ultrasound for 10 seconds, a mortality rate of 97.6% was reported (Wu, 2007).

Movement control

Plants can spread locally as nuts and fragments drift in water currents, but most attention should be given to addressing forms of human-mediated transport. A number of the United States have enacted legislation limiting the introduction, sale, transportation and trafficking of the species in an attempt to limit the rate of accidental or intentional introduction (USDA-NRCS, 2008).

Biological control

Much attention has been given to discovering methods of biological control. Grass carp Ctenopharyngodon idella has been used to control water chestnut (Hummel and Kiviat, 2004). However, grass carp are non-selective herbivores that will almost certainly harm native species. Much research has been forwarded on the use of herbivorous insects from the plant’s native range (Pemberton, 1999). Of the explored species, the leaf beetle Galerucella birmanica has shown the most promise. Although concerns regarding its specificity were forwarded early on in the research process, it has since been shown that although capable of completing its life cycle using native Brasenia schreberi, G. birmanica exhibits a strong preference in the laboratory and in the field for T. natans, with only occasional “spill-over” of beetles onto B. schreberi (Ding et al., 2006). 

Chemical control 

Some control of water chestnut has been documented with subsurface applications of triclopyr and 2,4-D amine. However, the maximum control achieved was only 66% (Poovey and Getsinger, 2007). Due to its limited efficacy, if chemical control is used, it should be accompanied by other forms of physical control and removal.

References

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Ding JQ; Blossey B; Du YuZhou; Zheng FuShan, 2006. Galerucella birmanica (Coleoptera: Chrysomelidae), a promising potential biological control agent of water chestnut, Trapa natans. Biological Control, 36(1):80-90. http://www.sciencedirect.com/science/journal/10499644

GBIF, 2008. Global Biodiversity Information Facilities. GBIF. http://data.gbif.org/

Groth AT; Lovett-Doust L; Lovett-Doust J, 1996. Population density and module demography in Trapa natans (Trapaceae), an annual, clonal aquatic macrophyte. American Journal of Botany, 83(11):1406-1415.

Hijikata Y; Yamada S; Yasuhara A, 2007. Herbal mixtures containing the mushroom Ganoderma lucidum improve recovery time in patients with herpes genitalis and labialis. Journal of Alternative and Complementary Medicine, 13(9):985-988. http://www.liebertonline.com/doi/abs/10.1089/acm.2006.6297

Hsuan Keng, 1978. Orders and families of Malayan seed plants. Synopsis of orders and families of Malayan gymnosperms, dicotyledons and monocotyledons. Singapore, Singapore: Singapore Univ. Press, 477 pp.

Hummel M; Findlay S, 2006. Effects of water chestnut (Trapa natans) beds on water chemistry in the tidal freshwater Hudson River. Hydrobiologia, 559:169-181.

Hummel M; Kiviat E, 2004. Review of world literature on water chestnut with implications for management in North America. Journal of Aquatic Plant Management, 42:17-28.

ISSG (IUCN SSC Invasive Species Specialist Group), 2013. Global Invasive Species Database (GISD). IUCN SSC Invasive Species Specialist Group. http://www.issg.org/database/welcome/

ISSG, 2007. Global Invasive Species Database (GISD). Invasive Species Specialist Group of the IUCN Species Survival Commission. http://www.issg.org/database

Ithaka Harbors Inc, 2008. Entry for TRAPA natans L. [family TRAPACEAE]. Aluka. Princeton, USA: Ithaka Harbors, Inc. www.aluka.org

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Marion L; Paillisson J, 2003. A mass balance assessment of the contribution of floatin-leaved macrophytes in nutrient stocks in an eutrophic macrophyte-dominated lake. Aquatic Botany, 75:249-260.

Mehrhoff LJ; Silander JA; Leicht SA; Mosher ES; Tabak NM, 2003. Invasive Plant Atlas of New England. Storrs, Connecticut, USA: University of Connecticut.

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Contributors

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08/04/08 Original text by:

Alison Mikulyuk, Wisconsin Dept of Natural Resources, Science Operations Center, 2801 Progress Rd, Madison, WI 53716, USA

Michelle Nault, Wisconsin Department of Natural Resources, 2801 Progress Rd, Madison, WI 53716-3339, USA

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