Water Caltrop -
[Water Chestnut, Buffalo Nut, Bat Nut, Devil Pod, Ling Nut; Singhara;
Pani-fol (India); Hishi (Japan); Lingjiao (China); Family
Lythraceae, Trapa bicornis and Trapa natans,
also Trapa rossica (endangered)]
These strange looking hooked pods are the seeds of floating water plants. They have been cultivated in India and China for more than 3000 years, and were much eaten in Europe from prehistoric times until near the end of the 19th century. They are now nearly extinct in Europe due to climate change and draining of swamps and wetlands, but Trapa natans has become a pest in North America, from Vermont to North Carolina and in Washington State.
The photo is of T. bicornis from East Asia, three in the shell, (3 inches point to point), and four shelled ones in the middle. T. natans is more triangular, with much shorter but sharper horns. It is the species listed as a "noxious weed" in much of the United States. Seeds do not float, and can remain viable for up to 12 years, which makes it difficult to eradicate. It's pretty hilarious that these are in the same plant family as the pomegranate.
More on Myrtles
Buying: These seed pods (T. bicornis) can be easily found in Asian markets here in Los Angeles, particularly in September and October. They are usually labeled "water chestnuts".
Cooking: These are usually cooked very simply and eaten out of hand as an appetizer or snack.
Eating: I usually eat them plain, and have found this method most effective:
Health & Nutrition: The seed meats are starchy and nutritious, with a good mineral content. They were a major food source in prehistoric Europe. Raw nuts are slightly toxic, but cooking destroys the toxin. As freshly harvested in Asia, they may have larval cysts of the intestinal parasite trematode Fasciolopsis buski, but these are destroyed by cooking.
In North America, the main health problem is from stepping on them. The sharp points, particularly of T. natans, can cause painful puncture wounds to feet.