[1] The species are floating annual aquatic plants, growing in slow-moving freshwater up to 5 metres (16 feet) 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 or the silhouette of a flying bat.

The water caltrop's submerged stem reaches 3.7 to 4.6 metres (12 to 15 feet) in length, anchored into the mud by very fine roots.

Investigations of archaeological material from southern Germany indicate that the prehistoric population of that region may well have relied significantly upon wild water caltrops to supplement their normal diet and, in times of cultivated cereal crop failure, water caltrops may even have been the main dietary component.

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.

In northern Italy, the nuts were offered roasted, much as sweet chestnuts (Castanea sativa) are still sold today.

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.

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.

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.

6, page 352: "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.

"[11] Water caltrop has been declared an invasive species from Vermont to Virginia,[12] and is classified as a noxious weed in Florida, North Carolina, and Washington.