|Boiled water caltrop (T. bicornis) seeds|
The water caltrop, water chestnut, buffalo nut, bat nut, devil pod, Singhara (Hindi: सिंघाडा)سنگھارا (Urdu) or Pani-fol (Hindi: পানিফল) is any of three extant species of the genus Trapa: Trapa natans, T. bicornis and the endangered Trapa rossica. The species are floating annual aquatic plants, growing in slow-moving water up to 5 meters deep, native to warm temperate parts of Eurasia and Africa. They bear ornately shaped fruits, which in the case of T. bicornis resemble the head of a bull, each fruit containing a single very large starchy seed. T. natans and T. bicornis have been cultivated in China and India for at least 3,000 years for the edible seeds.
The generic name Trapa is derived from the Latin word for "thistle," calcitrappa, as also is another common name for the water caltrop. The Chinese name is língjiǎo (菱角), líng meaning "caltrop" and jiǎo meaning "horn."
This plant should not be confused with the unrelated Eleocharis dulcis, also called water chestnut, an aquatic plant also raised for food since ancient times in China. Eleocharis dulcis is a sedge, whose round, crisp-fleshed corms are common in Western-style Chinese food.
The plant's name in Japanese is hishi, from the shape of the fruit. The same word is used to mean a diamond or lozenge shape. This in turn gives rise to the company name Mitsubishi meaning "three diamonds," a reference to the three red diamonds of the company's trademark.
The water caltrop's submerged stem reaches 12 to 15 ft (3.6 to 4.5 m) 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 at the water's surface. The floating leaves have saw-tooth edges and are ovoid or triangular in shape, 2–3 cm long, on inflated petioles 5–9 cm long, which provide added buoyancy for the leafy portion. Four-petalled white flowers form in early summer and are insect-pollinated. The fruit is a nut with four 0.5 in (1 cm), barbed spines. Seeds can remain viable for up to 12 years, although most will 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.
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 went extinct in North America prior to the Pleistocene). The oldest known fossils attributed to the genus, however, are of leaves from Cretaceous Alaska, referred to the species, T. borealis
Investigations of archaeological material from southern Germany indicate that the prehistoric population of that region may well have relied significantly upon wild water chestnuts to supplement their normal diet and, in times of cultivated cereal crop failure, water chestnuts may even have been the main dietary component. Today, water caltrop is so rare in Germany that it is listed as an endangered species.
Water caltrop has been an important food for worship as prayer offerings since the Chinese Zhou Dynasty. The Rites of Zhou (2nd century BC) mentioned that a worshipper "should use a bamboo basket containing dried water caltrops, the seeds of Euryale ferox and chestnuts" (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) indicates that water caltrop can help fever and drunkenness.
In India it is known as singhara or paniphal (eastern India) and is widely cultivated in fresh water lakes. The fruits are eaten raw or boiled. When the fruit has been dried, it is ground to a flour called singhare ka atta. Singhare ka atta is used in many religious rituals and can be consumed as a phalahar diet on the Hindu fasting days, the navratas.
It was possible to buy water chestnuts in markets all over Europe until 1880. In northern Italy the nuts were offered roasted, much as sweet chestnuts (Castanea sativa Mill.) are still sold today. In many parts of Europe water chestnuts were known and used for human food until the beginning of the 20th century. Today, however, it is a rare plant. There may be several reasons for its near extinction, such as climate fluctuations, changes in the nutrient content of water bodies, and the drainage of many wetlands, ponds and oxbow lakes.
Water chestnuts were introduced to North America around 1874, and escaped cultivation in the eastern United States, where they have been declared invasive species from Vermont to Virginia. They are also classified noxious weeds in Florida, North Carolina, and Washington.
Role in transmission of Fasciolopsiasis
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Fasciolopsiasis can be transmitted via the surfaces of these and other water plants. During the metacercarial stage in their life cycle, the larval flukes leave their water snail hosts, and swim away to form cysts on the surfaces of water plants, including the leaves and fruit of water caltrops. If infected water plants are consumed raw or undercooked, the flukes can infect pigs, humans and other animals.
Fasciolopsiasis results from infection by the trematode Fasciolopsis buski (Lankester, 1857) Odhner, 1902, the largest intestinal fluke of humans (up to 7.5 cm in length)
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- Karg, S. 2006. The water chestnut (Trapa natans L.) as a food resource during the 4th to 1st millennia BC at Lake Federsee, Bad Buchau (southern Germany). Environmental Archaeology 11 (1): 125–130.
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- The Times Of India http://health.indiatimes.com/articleshow/msid-207309,prtpage-1.cms
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- R. W. Pemberton (2002). "Water Chestnut". In Van Driesche, R., et al. Biological Control of Invasive Plants in the Eastern United States. USDA Forest Service.
- Bicornin, a new hydrolyzable tannin from Trapa bicornis, and revised structure of alnusiin. Yoshida T, Yazaki K, Memon M.U, Maruyama I, Kurokawa K and Okuda T, Heterocycles, 1989, volume 29, number 5, pages 861–864 INIST:6780591
- Multilingual taxonomic information from the University of Melbourne
- Species Profile- Water Chestnut (Trapa natans), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Water Chestnut.
- Trapa natans in West African plants - A Photo Guide.
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