Trapa bicornis, commonly known as bat nut, buffalo nut, horn nut, ling nut, or water caltrop, is an aquatic plant in the family Lythraceae, closely related to Trapa natans. It is native to South and Southeast Asia, especially India, southern China, and the Indo-Malay region. The species is named for its distinctive two-horned, bat-like fruit. Archaeological evidence suggests its consumption in ancient China and India, where it was used as both food and ritual offering. In Chinese culture, the nut was often linked to protective symbolism and was consumed during festivals.

The edible portion is the starchy seed inside the horned shell. Traditionally, the seeds are boiled, roasted, or ground into flour and incorporated into porridges, breads, and confections. In India, the dried nut flour is used much like Trapa natans flour (singhara), particularly in fasting foods and sweets. Today, the nut is valued as both a seasonal snack and a nutritive flour source in South and East Asian cuisines. While rich in carbohydrates, proteins, and minerals, raw bat nuts may harbor toxic microorganisms or parasites if collected from contaminated waters, thus thorough cooking is essential.