Water caltrop

Water caltrop
File:Illustration Trapa natans1.jpg
Illustration of Trapa natans, Otto Wilhelm Thomé, 1885
File:Water caltrop 1.jpg
Fruits
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Myrtales
Family:	Lythraceae
Subfamily:	Trapoideae
Genus:	Trapa L.

Trapa natans, the water caltrop, is a widespread species of flowering plant in the genus Trapa, family Lythraceae, grown as a food crop. Other vernacular names include buffalo nut, bat nut, devil pod, ling nut, mustache nut, singhara nut, water nut, and water chestnut, though this last name is commonly applied to Eleocharis dulcis.

It is a floating annual aquatic plant, growing in slow-moving freshwater up to 5 metres (16 feet) deep, native to warm temperate parts of Eurasia and Africa. It bears horned fruits. Each fruit contains a single large seed. T. natans has been cultivated in China and the Indian subcontinent for the edible seeds for at least 3,000 years.

In feudal Japan, the fruits were used as substitutes for iron caltrops, an area denial weapon; they were sharp enough to penetrate the shoes of the period. The Japanese manufacturing group Mitsubishi takes its name and its logo from the plant. The Bengali name for the samosa or fried triangular pastry snack, shingara, is likewise the name of the plant.

Description

Trapa natans forms floating leaf rosettes up to about 50 cm (20 in) across. It grows as an annual plant in shallow, slow-flowing fresh water, with a submerged stem up to some 2 m (7 ft) long and up to 6 mm (0.24 in) thick, rooted in the bottom mud and bearing thin leaves. The surface leaves are diamond-shaped, toothed, and up to 5 cm (2 in) long and 6 cm (2.5 in) wide. Their petioles (leaf stalks) are up to 21 cm (8.3 in) long.

The flowers have 4 white to pink petals up to 10 mm (0.4 in) long, 4 sepals, 4 stamens, and one pistil. There are initially 2 ovules in the ovary but only one develops. The flowers are mainly self-fertilising, occasionally insect-pollinated. The fruit is a nut (botanically a single-seeded drupe) with two to four barbed spines 12 mm (0.5 in) long that develop from the sepals. The plant contains an ellagitannin polyphenol called bicornin.

• Habit, with rosettes of leaves
  Habit, with rosettes of leaves
• Botanical illustration, 1804 Japanese agricultural encyclopedia Seikei Zusetsu
  Botanical illustration, 1804 Japanese agricultural encyclopedia Seikei Zusetsu

Evolution

Fossil record

File:Trapa americana SRUI SRDU img01.jpg

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). The oldest known fossils attributed to the genus are of leaves from Cretaceous Alaska, referred to the species, T. borealis.

Taxonomy

Trapa natans is the type species of its genus, named by the Swedish botanist Carl Linnaeus in his Species Plantarum in 1753. The generic name Trapa is derived from a late Latin word for a caltrop, calcitrappa, an area denial weapon. The specific name natans is the Latin for swimming or floating, from the verb natare, "to swim". There are eight named varieties of T. natans. The Scottish surgeon and botanist William Roxburgh described Trapa bispinosa as a species in 1815, but botanists treat this as a variety of T. natans; "T. bicornis" was described by the Swedish botanist Pehr Osbeck as a species in 1757, but is treated as a synonym of T. natans var bispinosa. T. rossica was described by the Russian botanist Viktor Nikolayevich Vassiljev and published by Vladimir Leontyevich Komarov in 1949; it is treated as a synonym for T. natans var natans.

• The generic name is derived from a Latin word for a caltrop.
  The generic name is derived from a Latin word for a caltrop.
• Trapa natans, 4-horned fruit
  Trapa natans,
  4-horned fruit
• Trapa natans var bicornis, 2-horned fruit
  Trapa natans var bicornis,
  2-horned fruit

Subtaxa

The following varieties are accepted:

• Trapa natans var. africana Brenan – Tanzania, Uganda
• Trapa natans var. bispinosa (Roxb.) Makino – Tropical and southern Africa, Indian Subcontinent, eastern Asia
• Trapa natans var. japonica Nakai – Korea, Japan
• Trapa natans var. magnicorona (Z.T.Xiong) B.Y.Ding & X.F.Jin – Russian Far East, eastern China, Korea, Japan
• Trapa natans var. natans – North Africa, Eurasia
• Trapa natans var. pseudincisa (Nakai) ined. – Russian Far East, eastern China, Korea, Japan
• Trapa natans var. quadricaudata (Glück) B.Y.Ding & X.F.Jin – Cameroon, KwaZulu-Natal, Southeast Asia, eastern China, Russian Far East, Japan
• Trapa natans var. quadrispinosa (Roxb.) Makino – Himalayas to Japan

Distribution and habitat

The habitat of Trapa natans is shallow, slow-flowing fresh water with bottom mud. The species prefers warm, nutrient-rich and sunny areas; the bottom is usually soft and rich in organic matter.

Native

Trapa natans is widely distributed across Eurasia and Africa. In Europe, it is extinct in Spain and Sweden, and is absent from Portugal, the British Isles, Norway, and Finland. It is so rare in Germany that it is listed as an endangered species. In 2024, it was predicted that the species, whose European distribution shrank between 1950 and 1980, will continue the expansion it began around 2000 until at least 2080, as global warming creates warmer conditions in the north of Europe. In Southeast Asia, it is present in Sumatra and Java; it is found, too, across the Philippines and Japan.

Introduced

In eastern North America, T. natans has been declared an invasive species from Vermont to Virginia, and is classified as a noxious weed in Florida, North Carolina, and Washington. As of 2020, both T. natans and T. bicornis were growing wild in US waterways. In 1956 T. natans was banned for sale or shipment in the US, subject to a fine and imprisonment. The law was repealed in 2020. T. natans was introduced to Massachusetts around 1874 as a planting in the Harvard University Botanic Garden, and from there intentionally spread into nearby ponds and waterways.

Ecology

Competition

File:Expedition 10.jpg

The plant can form a thick floating mat covering many hectares.

Trapa natans, being widespread, occurs alongside many other aquatic plants. In suitable conditions its rapid growth and ability to form a canopy over the water enable it to monopolise areas of water. Its ability to produce large numbers of seeds then enable it to maintain a dense coverage where it has established itself. The species can trap 95% of the sunlight falling on an area, depriving other plants of light for photosynthesis. Respiration by its submerged parts depletes oxygen in the water, which can cause methane to be produced, acidification of the water, and eutrophication. It modifies its own ecosystem by creating a thick surface canopy of dead leaves.

Pests and diseases

File:Galerucella nymphaeae 1.jpg

Galerucella nymphaeae, the waterlily leaf beetle of Europe, eats the plant's floating leaves.

The species is grazed in particular by two species of chrysomelid leaf beetle, Galerucella nymphaeae in North America and Europe, and G. birmanica in Asia: larvae and adults of both species eat the leaf blade. Curculionid weevils including Nanophyes japonica appear to be specialised feeders on the floating leaves including their petioles. The armyworm moth Spodoptera litura is a pest of T. natans cultivation. The crambid moth Elophila interruptalis eats and kills the central bud of the plant's shoot, killing it and stopping growth.

Among mammals, the beaver, coypu, muskrat and some squirrels eat the fruits and other parts of the plant. Among aquatic birds, swans have been recorded as eating the plant.

Ascomycete fungi such as Cercospora, Botrytis cinerea, and Cochliobolus spicifer occur with the plant, along with the basidiomycete pathogen Agroathelia rolfsii.

Parasite transmission

File:Fasciolopsis buski egg 08G0039 lores.jpg

Eggs of the parasite Fasciolopsis buski, transmitted on the surface of T. natans fruits

Fasciolopsiasis is a disease resulting from infection by the trematode Fasciolopsis buski, an intestinal fluke of humans, endemic in China, Southeast Asia, and India. The fluke can be transmitted via the surfaces of water plants, generally T. natans fruits. During the metacercarial 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.

Interactions with humans

Use as food

The fruits and seeds are edible raw or cooked. Archaeological finds 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.

Water caltrop has been an important food for prayer offerings since the Chinese Zhou dynasty. The Rites of Zhou (second century BC) required worshippers to carry bamboo baskets of dried water caltrops (加籩之實，菱芡栗脯).

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 navratas.

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. The plant has however become rare 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.

• Water caltrop field, Taiwan
  Water caltrop field, Taiwan
• Boiled singhara (Trapa natans) for sale, Bhopal, India
  Boiled singhara (Trapa natans) for sale, Bhopal, India

In culture

In feudal Japan, water caltrop fruits were sometimes used as substitutes, tennenbishi for iron caltrops, makibishi. Both types were sharp enough to penetrate the soles of the waraji sandals worn by warriors of the period. The manufacturing group Mitsubishi takes its name, which means "three rhombuses" or "three water caltrops" (Japanese 三 mitsu, "three", 菱 hishi "water caltrop"), and its logo from the plant. In Eastern India, the samosa (a fried triangular pastry) is called सिंघाड़ा shingara after the fruit.

• The company name Mitsubishi and its logo denote the fruit.[28]
  The company name Mitsubishi and its logo denote the fruit.
• Shingara, meaning water caltrop, is the Bengali name for samosas, fried triangular pastry snacks.[29]
  Shingara, meaning water caltrop, is the Bengali name for samosas, fried triangular pastry snacks.

External links

• 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.