Trapa natans (PROSEA)
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Introduction |
Trapa natans L.
- Protologue: Sp. pl. 1: 120 (1753).
- Family: Trapaceae
- Chromosome number: 2n= 48, 96
Synonyms
- Trapa bicornis Osbeck (1757),
- Trapa cochinchinensis Lour. (1790),
- Trapa bispinosa Roxb. (1815).
Vernacular names
- Water chestnut, water caltrop, Singhara nut (En)
- Indonesia: lengkat, lengkong, salaikat (Jakarta, Java)
- Cambodia: krachap
- Thailand: kra chap (central), khao khwaai (northern), ma ngaeng (Chiang Rai)
- Vietnam: củ ấu, ấu nước.
Origin and geographic distribution
T. natans occurs in southern Europe, Africa and temperate, subtropical and tropical Asia. It is rare in the Malesian region, known only from southern Sumatra and western Java, where it was possibly introduced by Chinese people. It is cultivated in India, Indo-China and southern China, mainly for its edible fruits.
Uses
In Vietnam and Cambodia a decoction or infusion of the fruits is used in traditional medicine to treat fever and headache, and as a tonic. In China the fruits are additionally used as a thirst quencher and to treat sunstroke. They are considered to be tonic and to heal stomach cancer in Japan.
The fruits are faintly sweet and eaten as a delicacy after being cooked. They should not be confused with the tubers of Chinese water chestnut (Eleocharis dulcis (Burm.f.) Trinius ex Henschel), which are commonly used in stir-fried Chinese dishes. In Indo-China flour is prepared from the seeds, which is sweetened with sugar and honey and made into pastry. T. natans is also used as an ornamental aquatic plant. It is reputed for its ability to absorb large amounts of toxic metals from polluted water.
Properties
Extracts of T. natans fruits showed distinct antimicrobial activity against gram-positive and gram-negative bacteria, and also significant cytotoxic activity, e.g. against HeLa cells in vitro. Gallic acid was isolated as a cytotoxic constituent. In tests, an extract also inhibited glycosyl transferase, thus preventing the formation of dental plaque, and it showed distinct activity against several plant viruses. A screening showed that T. natans may be a potential source of antioxidants. Several tannins have been isolated from T. natans leaves.
Per 100 g dry weight, fruits contain up to 70 g starch, about 10 g protein, 7 g sugar, 0.5 g fat and 0.7 g fibre. The starch is suitable for uses as tablet disintegrant in pharmaceuticals. The fruits can be eaten raw, but this is not recommended as they may contain parasites, particularly flukes, from contaminated water.
Botany
- An annual, aquatic, floating herb with slender main axis up to 4 m long, branched or not; adventitious roots developing from leaf scars of submerged leaves, with many filiform segments.
- Leaves dimorphic; submerged ones opposite, linear, entire, sessile, caducous; floating ones alternate, in rosettes, rhombic to deltoid, (1-)3-7 cm × (1-)4-9 cm, the upper margins dentate, glabrous to hairy beneath, petiole 6-21 cm long, spongy and more or less inflated about the middle; stipules small, scarious, divided to the base.
- Flowers solitary in axils of upper leaves, bisexual, regular, 4-merous, pedicelled; sepals lanceolate to narrowly triangular, 4-7 mm long; petals free, oblanceolate to obovate, 8-16 mm long, white; stamens inserted at the base of the ovary; disk surrounding the ovary, crenulate; ovary half-inferior, 2-celled, style with capitate stigma.
- Fruit a top-shaped drupe up to 3 cm wide and long, pericarp blackish, soon disappearing, endocarp hard, very variably 2-4-horned, 1-seeded.
- Seed with woody testa; cotyledons very unequal, 1 almost vestigial.
A single seed may give rise to 10-15 rosettes of floating leaves, and each rosette may produce up to 20 fruits. The fruits fall to the bottom of the water, and the seeds may remain viable for up to 12 years. This all contributes to the large growing-power of T. natans under suitable conditions.
Trapa is the only genus of the Trapaceae, but has often been included in the Onagraceae. The number of species in the genus is still under debate; some botanists maintain up to 30 species, but most recognize only a few or even only one polymorphic species (then usually a number of varieties is distinguished). This latter view is followed here. The fruit is most variable, especially the number and shape of its horns. Many fossil species have been described.
Ecology
T. natans occurs in ponds and swamps with slowly flowing or stagnant, eutrophic water in lowland areas, where it roots in soft mud. It cannot stand brackish or acid water. T. natans is best grown in shallow ponds, which hold water throughout the year; it requires full sun.
Management
T. natans is commercially cultivated in China and India, where maximum yields of 4-5 t of fruits per ha have been obtained. It is propagated by seeds, but in China stem segments and axillary buds have been cultured successfully on a half-strength Murashige and Skoog medium supplemented with growth hormones. Blight caused by Sclerotium rolfsii is the major disease in China, and the beetle Galerucella birmanica is the most serious pest in Asia.
T. natans is considered a serious weed in some regions, e.g. in the eastern United States, where it clogs waterways locally and where special control programmes exist.
Genetic resources
T. natans is found only very locally in the Malesian region, mainly in Java, and it is not clear whether it only descends from cultivation or also occurs naturally in this region. In view of its enormous variability worldwide, there is ample scope for evaluating the genetic resources and possible breeding activities.
Prospects
Both the nutritious fruits and their medicinal properties seem to justify more research on more intensive utilization of T. natans in the Malesian region. Efforts to cultivate this plant resource should take into account the potential danger of it becoming a serious weed.
Literature
247, 334, 504, 671, 764.
Other selected sources
121, 250, 966.
Main genus page
Authors
Rosna Mat Taha
