The water caltrop is any of three extant species of the genus Trapa: Trapa natans, T. bicornis and the endangered Trapa rossica. It is also known as water chestnut, buffalo nut, bat nut, devil pod, ling nut, lin kok, ling kio nut or singhara.

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 or the silhouette of a flying bat. Each fruit contains 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.