Ling Jiao

Ling Jiao, 菱角, also known as water caltrops and water chestnuts, are the nut-like seeds of any species of Trapa, a genus of waterweed that produces large, ornately shaped seeds. Most examples of ling jiao refer to the species T. natans, which is shaped vaguely like a four-pointed chestnut, or T. bicornis, which is shaped like a bull's head or a stylized bat in flight. The third living species, T. rossicus, is an endangered species restricted to marshlands of the Ukraine. T. natans and T. bicornis are found throughout temperate and subtropical Eurasia, but, due to destruction and drainage of wetlands, they are very rare or endangered in Europe. Ling jiao have an extensive fossil record starting from the Cretaceous of Alaska, where fossil leaves have been found. From the Eocene onward, fossil seeds of numerous distinct species are found in freshwater strata of Eurasia and North America: species of Trapa would die out in North America near the end of the Pliocene.

Ling jiao have been eaten by ancient European and Asian people since prehistoric times.

The seed is either steamed or roasted, then eaten like the similar-tasting, but unrelated chestnut. It is inadvisable to eat the raw seed, as, it is mildly poisonous, and, if not cleaned, can be a source of parasitic worms.

In Chinese food therapy, ling jiao nourishes dryness and resolves thirst, especially thirst caused by summer heat, resolves diarrhea caused by spleen deficiency, and, unlike many cool foods, nourishes and harmonizes the spleen and stomach. Ling jiao should not be eaten if the patient has malaria, or has diarrhea due to causes other than spleen deficiency.