View source for Water caltrop

{{Short description|Genus of flowering plants}}
{{Distinguish|Chinese water chestnut}}
{{automatic taxobox
 | name = Water caltrop
 | image = Illustration Trapa natans1.jpg
 | image_caption = ''Trapa natans''
 | parent_authority = [[Joachim Otto Voigt|Voigt]]
 | taxon = Trapa
 | authority = [[Carl Linnaeus|L.]]
 | type_species = ''Trapa natans''
 | type_species_authority = L.
 | subdivision_ranks = Species
 | subdivision = 
*''[[Trapa natans]]''
*''[[Trapa bicornis]]''
*''[[Trapa rossica]]''
}}

The '''water caltrop''' is any of three extant species of the [[genus]] ''Trapa'': '''''Trapa natans''''', '''''Trapa bicornis''''' and the endangered '''''Trapa rossica'''''. It is also known as '''buffalo nut''', '''bat nut''', '''devil pod''', '''ling nut''', '''mustache nut''', '''singhara nut''' or '''water chestnut'''.<ref>{{cite web |title=M.M.P.N.D. - Sorting Trapa names |url=https://www.plantnames.unimelb.edu.au/Sorting/Trapa.html |website=www.plantnames.unimelb.edu.au |access-date=24 August 2022 |quote=Generally there is a lot of confusion throughout the world about the vegetable called "water chestnut". The first confusion is between the European Trapa and the Chinese Eleocharis. Then people get lost within each of those genera because common names have never been properly matched to stabilised botanical names.}}</ref>

The species are floating [[annual plant|annual]] [[aquatic plant]]s, growing in slow-moving freshwater up to {{Convert|5|m|abbr=off}} deep, native to warm temperate parts of Eurasia and Africa. They bear ornately shaped fruits, which in the case of ''T.&nbsp;bicornis'' resemble the head of a bull or the [[silhouette]] of a flying [[bat]]. Each fruit contains a single very large, starchy seed. ''T.&nbsp;natans'' and ''T.&nbsp;bicornis'' have been cultivated in China and the Indian subcontinent for the edible seeds for at least 3,000 years.

== Description ==

{{More citations needed section|date=April 2021}}

The water caltrop's submerged stem reaches {{convert|12|to|15|ft|m|abbr=off|order=flip}} in length, anchored into the mud by very fine roots. It has two types of [[leaves]]: finely divided, feather-like submerged leaves borne along the length of the stem, and undivided floating leaves borne in a [[rosette (botany)|rosette]] at the water's surface. The floating leaves have saw-tooth edges and are ovoid or triangular in shape, {{Convert|2-3|cm|in|frac=4|abbr=off}} long, on inflated petioles {{Convert|5-9|cm|frac=2|abbr=on}} long, which provide added buoyancy for the leafy portion.

Four-petalled white flowers form in early summer and are [[insect-pollinated]].<ref>{{Cite web |last=Erika |date=2024-01-06 |title=How Do Water Chestnuts Grow? Plant Characteristics, Planting, Growth Cycle, Harvesting, Pests, Diseases, And Culinary Uses - AquaWorldHub |url=https://aquaworldhub.com/how-do-water-chestnuts-grow/ |access-date=2025-09-06 |website=aquaworldhub.com |language=en-US}}</ref> The fruit is a nut with four {{convert|1/2|in|cm|0|abbr=on|order=flip}} barbed spines. Seeds can remain viable up to 12 years, although most germinate within the first two years.

The plant spreads by the rosettes and fruits detaching from the stem and floating to another area on currents or by fruits clinging to objects, and animals.

{{gallery |mode=nolines
|File:Water caltrop 1.jpg|Plant
|File:Trapa_natans0.jpg|[[rosette (botany)|Rosette]] of leaves
|File:Singhara or Water Chestnut in Bhopal, October 2025 (91637).jpg| Boiled Singhara or Trapa natans for sale
}}

=== Chemistry ===

[[Bicornin]] is an [[ellagitannin]] found in ''T. bicornis''.<ref>{{Cite journal |last1=Yoshida |first1=T. |last2=Yazaki |first2=K. |last3=Memon |first3=M.U. |last4=Maruyama |first4=I. |last5=Kurokawa |first5=K. |last6=Okuda |first6=T. |year=1989 |title=Bicornin, a new hydrolyzable tannin from ''T. bicornis'', and revised structure of alnusiin |url=https://archive.org/details/sim_heterocycles_1989-05-01_29_5/page/n34 |journal=Heterocycles |volume=29 |issue=5 |pages=861–864 |doi=10.3987/COM-89-4951 |id={{INIST|6780591}} |url-access=registration|doi-access=free }}</ref>

== Taxonomy ==

=== Phylogeny ===

[[file:Trapa americana SRUI SRDU img01.jpg|thumb|right|upright|''[[Trapa americana]]'', [[Latah Formation]], North America]]

The genus has an extensive fossil record, with numerous, distinctive species. Undisputed fossilized seeds have been found in [[Cenozoic]] strata starting from the [[Eocene]] throughout [[Europe]], [[China]] and [[North America]] (though the genus became extinct in North America prior to the [[Pleistocene]]).<ref>{{Cite web|url=https://books.google.com/books?id=rN4qAQAAIAAJ&q=trapa&pg=RA2-PA266|title=Torreya|date=August 3, 1912|publisher=Torrey Botanical Club.|via=Google Books}}</ref> The oldest known fossils attributed to the genus are of leaves from [[Cretaceous]] [[Alaska]], referred to the species, ''T.&nbsp;borealis''.<ref name="Hollick">{{cite book|last=Hollick|first=Charles Arthur|title=The Tertiary floras of Alaska, Issues 181–184|year=1936|publisher=United States Government Print Office|pages=156|url=https://books.google.com/books?id=bmvnAAAAMAAJ&q=cretaceous+%22trapa%22+fossil&pg=PA156}}</ref>

=== Etymology ===

The generic name ''Trapa'' is derived from the Latin word for "[[thistle]]", {{Lang|la|calcitrappa}}, as also is another common name for the water [[caltrop]].{{citation needed|date=May 2021}}

The plant's name in Japanese is {{Transliteration|ja|hishi}}, a word that is also used to mean "a diamond or lozenge shape, a rhombus". The manufacturing group [[Mitsubishi]] takes its name and logo of three lozenges from the water caltrop.<ref>{{cite web |title=Mitsubishi Mark |url=https://www.mitsubishi.com/en/profile/group/mark/ |access-date=14 May 2021 |website=www.mitsubishi.com}}</ref>

It is called ''{{Transliteration|sa|Shringataka}}'' in [[Sanskrit]],<ref>{{cite web |date=9 August 2016 |title=Shringataka |url=https://www.easyayurveda.com/2016/08/09/shringataka-trapa-bispinosa/ |access-date=8 December 2021}}</ref> which is shortened to ''{{Transliteration|hi|Shingara}}'' in [[Hindi]] language. In Eastern India, the [[samosa]] (a fried or baked [[pastry]]) is also called Shingara because its shape resembles that of the Shingara fruit.

== Invasiveness ==
Water caltrop has been declared an [[invasive species]] from [[Vermont]] to [[Virginia]],<ref>{{cite conference |author=R. W. Pemberton |year=2002 |title=Water Chestnut |url=http://www.invasive.org/eastern/biocontrol/3WaterChestnut.html |publisher=USDA Forest Service |archive-url=https://web.archive.org/web/20090908105853/http://www.invasive.org/eastern/biocontrol/3WaterChestnut.html |archive-date=2009-09-08 |access-date=2007-07-14 |book-title=Biological Control of Invasive Plants in the Eastern United States |editor=Van Driesche, R. |display-editors=etal |url-status=dead}}</ref> and is classified as a noxious weed in [[Florida]], [[North Carolina]], and [[Washington (state)|Washington]].<ref>{{cite web |title=USDA Plants Database |url=https://plants.usda.gov/java/profile?symbol=TRBI5}}</ref> As of 2020, both ''T. natans'' and ''T. bicornis'' have been reported growing wild in the waterways of the United States.<ref name="BayJournal">{{cite news |last=Cox |first=Jeremy |date=July 27, 2020 |title=Invasive water plant poised to overwhelm Potomac watershed |url=https://www.bayjournal.com/news/fisheries/invasive-water-plant-poised-to-overwhelm-potomac-watershed/article_83f2fc70-c830-11ea-8425-f74212a7eb1b.html |access-date=July 29, 2020 |work=Bay Journal}}</ref> In 1956 ''T. natans'' was banned for sale or shipment in the US, subject to a fine and imprisonment.<ref name="US-ban-law" /> The law was repealed in 2020.<ref>{{Cite web |title=18 U.S. Code § 46 - Repealed. Pub. L. 116–260, div. O, title X, § 1002(1), Dec. 27, 2020, 134 Stat. 2155] |url=https://www.law.cornell.edu/uscode/text/18/46 |website=LII / Legal Information Institute}}</ref>
''T. natans'' was introduced to the US state of Massachusetts around 1874 as a planting in the Harvard University Botanic Garden. Staff gardener Louis Guerineau took it upon himself to throw seeds into Fresh Pond and other Cambridge waterways. This came to the attention of Medford-based botanist George E. Davenport, who decided to bring seeds and live plants to his friend Minor Pratt, in Concord. He and Pratt seeded a pond near the Sudbury River, and he suspected Pratt of conducting additional distributions. As early as 1879, concern was voiced by botanist [[Charles Sprague Sargent]], director of Boston's [[Arnold Arboretum]], that this non-native species threatened to become a nuisance, based on dense growths reported in Cambridge. Davenport confessed in 1879:<ref>{{Cite journal |last=Davenport |first=Geo. E. |date=1879 |title=Trapa natans |url=https://www.jstor.org/stable/2476842 |journal=Bulletin of the Torrey Botanical Club |volume=6 |issue=58 |pages=352 |issn=0040-9618 |jstor=2476842}}</ref><blockquote>I have several times had plants of ''Trapa natans'' that were collected in the vicinity of Boston, during the present year, brought to me for identification, and I have entertained no doubt as to the manner of its introduction into waters outside Cambridge Botanic Garden. But that so fine a plant as this, with its handsome leafy rosettes and edible nuts, which would, if common, be as attractive to boys as hickory nuts now are, can ever become a 'nuisance' I can scarcely believe.</blockquote>

== Conservation ==
Water caltrop is so rare in Germany that it is listed as an [[endangered species]].<ref>{{Cite web |title=Trapa natans L. |url=https://www.floraweb.de/php/artenhome.php?suchnr=6005& |access-date=2024-03-29 |website=www.floraweb.de}}</ref>

== Parasite transmission ==

[[Fasciolopsiasis]] is a disease resulting from infection by the [[Trematoda|trematode]] ''[[Fasciolopsis buski]]'', an intestinal [[Liver fluke|fluke]] of humans, endemic in China, Southeast Asia, and India. The fluke can be transmitted via the surfaces of water plants, generally ''T. natans'' seedpods. During the [[cercaria|metacercaria]]l stage in their lifecycle, the larval flukes leave their water snail hosts, and swim away to form cysts on the surfaces of the plants. If infected plants are consumed raw or undercooked, the flukes can infect pigs, humans, and other animals.<ref>{{cite book |last=Brack |first=Manfred |chapter=Trematodes |title=Agents Transmissible from Simians to Man |year=1987 |publisher=Springer |pages=393–426 |doi=10.1007/978-3-642-71911-0_8 |isbn=978-3-642-71913-4 |chapter-url=https://link.springer.com/chapter/10.1007/978-3-642-71911-0_8}}</ref>

== Uses ==

The fruits are edible raw or cooked, and the seeds can be eaten as well.<ref>{{Cite book |title=The Complete Guide to Edible Wild Plants |publisher=[[Skyhorse Publishing]] |others=[[United States Department of the Army]] |year=2009 |isbn=978-1-60239-692-0 |location=New York |pages=108 |language=en-US |oclc=277203364}}</ref> It is also eaten on the occasion of [[Mid-Autumn Festival]] in the [[East Asian cultural sphere|Sinosphere]].

=== Historical uses ===
Investigations of archaeological material from southern Germany indicate that the prehistoric population of that region may have relied significantly upon wild water caltrops to supplement their normal diet and, in times of cultivated cereal crop failure, water caltrops may have been the main dietary component.<ref name="karg">{{Cite journal |last=Karg |first=S. |date=2006 |title=The water chestnut (''Trapa natans'' L.) as a food resource during the 4th to 1st millennia BC at Lake Federsee, Bad Buchau (southern Germany) |url=https://www.researchgate.net/publication/228643256 |journal=Environmental Archaeology |volume=11 |issue=1 |pages=125–130 |bibcode=2006EnvAr..11..125K |doi=10.1179/174963106x97106 |issn=1461-4103}}</ref>

Water caltrop has been an important food for worship as prayer offerings since the Chinese [[Zhou dynasty]]. The [[Rites of Zhou]] (second century BC) mentioned that a worshipper "should use a bamboo basket containing dried water caltrops, the seeds of ''[[Euryale ferox]]'' and [[caltrops]]" (加籩之實，菱芡栗脯). The ''Chinese Herbal Medicine Summary'' (本草備要 published in 1694, written by Wang Ang 汪昂) claims that water caltrop can help [[fever]] and drunkenness.{{cn|date=May 2021}}

In India and Pakistan, it is known as ''singhara'' or ''paniphal'' (eastern India) and is widely cultivated in freshwater lakes. The fruits are eaten raw or boiled. When the fruit has been dried, it is ground to a flour called ''singhare ka atta'', used in many religious rituals, and can be consumed as a ''phalahar'' (fruit diet) on the [[Hindu]] fasting days, the [[Navratri|navratas]].<ref>{{cite news |title=Tips To A Healthy 'Navratra' |url=http://health.indiatimes.com/articleshow/msid-207309,prtpage-1.cms |url-status=dead |archive-url=https://web.archive.org/web/20190703152241/http://health.indiatimes.com/articleshow/msid-207309,prtpage-1.cms |archive-date=2019-07-03 |access-date=2010-02-03 |work=The Times Of India}}</ref>

It was possible to buy water caltrops in markets all over Europe until 1880. In northern [[Italy]], the nuts were offered roasted, much as sweet chestnuts (''[[Castanea sativa]]'') are still sold today. In many parts of Europe, water caltrops were known and used for human food until the beginning of the 20th century. Today, however, it is a rare plant in Europe. Several reasons for its near extirpation exist, such as climate fluctuations, changes in the nutrient content of water bodies, and the drainage of many wetlands, ponds, and oxbow lakes.<ref name="karg" />

<gallery class="center" mode="nolines" widths="160px" heights="160px">
File:Trapa natans seeds.jpg|''T. natans'' fruits
File:Water-caltrops.jpg|Boiled ''T. bicornis'' seeds
File:Taiwan 2009 Tainan City Water Caltrop Field FRD 7922.jpg|Water caltrop field in Taiwan
File:Leiden University Library - Seikei Zusetsu vol. 28, page 024 - 芰 - Trapa sp, 1804.jpg|1804 Japanese agricultural encyclopedia ''[[Seikei Zusetsu]]''
File:Krachap Khao Khwai กระจับเขาควาย -นครนายก 02.jpg|Boiled water caltrop on sale in Thailand
</gallery>

== References ==

{{Reflist|refs=
<ref name="US-ban-law">{{cite act|url=http://www.govinfo.gov/app/details/USCODE-2011-title18/USCODE-2011-title18-partI-chap3-sec46|title=Transportation of water hyacinths|legislature=[[United States Congress]]|date=1 August 1956|type=Bill|index=18 U.S. Code § 46}}</ref>
}}

== External links ==

{{Commons category|Trapa}}

{{Wikispecies|Trapa}}
{{unimelb|Trapa.html}}
* [https://www.invasivespeciesinfo.gov/aquatic/plants/water-chestnut Species Profile - Water Chestnut (''Trapa natans'')], National Invasive Species Information Center, [[United States National Agricultural Library]]. Lists general information and resources for Water Chestnut.

{{WestAfricanPlants|Trapa natans}}
{{Taxonbar|from1=Q2487780|from2=Q161110}}
{{Authority control}}

[[Category:Edible nuts and seeds]]
[[Category:Hong Kong cuisine]]
[[Category:Lythraceae]]

{{interwiki extra|qid=Q161110}}