Water caltrop

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The water caltrop or water chestnut refers to two species of the genus Trapa - T. natans and T. bicornis. Both 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 that resemble the head of a bull, each containing a single very large starchy seed. It has been cultivated in China for at least 3,000 years for these seeds, which are boiled and sold as an occasional streetside snack in the south of that country.

Etymology

The generic name Trapa is derived from the latin word calcitrappa (thistle), as is the name caltrop. Caltrop also refers to an iron weapon used in medieval times, with four points, designed to pierce the hooves of enemy cavalry horses. A similar device was used during World War II to destroy the truck tires of enemy convoys.[A Horny Bull's Head], from [Wayne's Word], October, 1995

This plant should not be confused with the unrelated Eleocharis dulcis, also called water chestnut, an aquatic plant 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.

Biology

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 born along the length of the stem, and undivided floating leaves born 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-petaled 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 rosette and fruits detaching from the stem and floating to another area on currents or by fruits clinging to objects, birds and other animals.

History

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, may even have been the main dietary component. 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.

It was possible to buy water chestnuts in markets all over Europe until 1880 AD. In northern Italy the nuts were offered roasted, much as sweet chestnuts (Castanea sativa Mill.) are still sold today. At many places in Europe water chestnuts were known and used for human food until the beginning of the 20th century. Today, however, it is a rare plant. The reasons for its near extinction might be due to several factors, such as climatic fluctuations, changes in the nutrient content of the water bodies, and the drainage of many wetlands, ponds and oxbow lakes. 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.

It was introduced to North America around 1874, and escaped cultivation in the eastern United States, where it has become an invasive species from Vermont to Virginia.

Disease

Fasciolopsiasis can be transmitted by the surface of the plants.

Notes