What Are Water Caltrops And How Do You Cook With Them?

Plants that are common and desired in one area of the world may have a completely different reputation elsewhere, and that's especially true for water caltrops. These edible nuts come from a plant that's long been cultivated in Asia and Europe for food. However, when the plants were introduced to the U.S., people found out the hard way that the plant thrived to the point of being invasive. As a result, water caltrops aren't commonly grown in the U.S., and it's not considered a very common food overall in this country.

Still, you can find water caltrops at certain markets as a seasonal treat. The shells of the nuts are blackish-brown, and one version — the one you'll most likely find for sale — has two points extending from either side that make the nut look like something out of a horror movie. When cooked, the nut itself is actually very nutritious, and it's a great addition to stir-fry. It's also a tasty snack when eaten on its own. Here's a look at water caltrops and how you're supposed to cook them.

Water caltrops are the seeds, nuts, pods, or fruit — you'll see all four terms used — of plants in the Trapa genus. You'll also hear the name used to refer to the entire plant. Most water caltrops that you see online are Trapa natans, and they have four spikes. The water caltrops you see in markets are generally from Trapa bicornis, and they have two spikes. T. bicornis looks a lot like a bat or even the head of a demon, and a common name for the pods is "bat nut."

The plant itself is aquatic, with an admittedly very pretty rosette of leaves floating above a stem that's stuck in mud. The edible seed pods grow at the end of that stem in the mud, and each plant can produce as many as 20 pods. Note that the seed pods have to be cooked and can't be eaten raw, despite what some websites say. Believe it or not, water caltrops are from the same taxonomic family as pomegranates.

Water caltrop plants are native to the Mediterranean region and more temperate areas of Asia, and they were introduced to the U.S. as ornamental plants. As so often happens with imported ornamentals, however, the plants escaped and started taking over waterways. It turns out that in the U.S., water caltrop plants are highly invasive, and many lakes and rivers have had the aquatic life choked out of them by the fast-growing rosettes.

If you're in the U.S., water caltrops grow just about anywhere they can get into fresh water. It's a particular problem on the East Coast — especially in New England and the mid-Atlantic states — although western states like Arizona consider it to be a noxious weed, too. You can't buy it in the South, either. It will grow in the relatively still waters of a lake and the moving waters of a river, as long as the water is fresh and rich in nutrients, and as long as the rosette of leaves can remain on the surface of the water. The plant, once established, is very hard to remove because the spiky pods act like anchors in the mud of the lake or riverbed.

The plant can spread either through pod dispersal or broken stems and leaves. The pods don't travel far; if one breaks away from another plant, it soon settles nearby due to its weight dragging it down. If leaves and stems break away from another plant, however, those can float far downstream and become established in another part of the body of water. It's also possible for another structure like a boat to accidentally pull some of the leaves and stems into other parts of the water.

Most cultivated water caltrop plants are grown in Asia. The plant is sometimes grown in gardens in Europe, where it's considered endangered.

A very common name for the water caltrop is "water chestnut," but this is more confusing than helpful because these are not the same water chestnuts that you buy sliced in a can. Those crunchy morsels are from the genus and species Eleocharis dulcis. They're the sweet, firm chestnuts you get in most stir-fries, especially in the U.S. While they're technically called Chinese water chestnuts, they're not always referred to by that full name, which adds to the confusion.

This use of "water chestnut" for the two foods leads to a lot of mix-ups on websites where people label pictures of both round Chinese water chestnuts and spiky water caltrops as T. natans. Those who are seeing water caltrop pods for the first time also sometimes become amazed upon hearing that they're called water chestnuts, thinking that they're looking at an actual Chinese water chestnut pod. Luckily, most sites and people make the distinction between the two.

Water caltrops have that name because the nuts, especially the four-pointed T. natans, resemble a weapon used for disruption in battle. Caltrops are multi-pronged devices that have been used for centuries, first to disable horses by injuring their hooves, and later to puncture tires. Sometimes you'll hear about caltrops being used for vandalism, too. The Trapa portion of the plant's scientific name is derived from calcitrippa, which is the Latin word for the caltrop used in battle.

With a resemblance to weaponry, stereotypical devils, bats, and water buffalo heads, you know there's a treasure trove of folklore associated with these nuts, at least for T. bicornis, the two-pointed water caltrop. Its resemblance to a bat has made it a must-have food during the Mid Autumn Festival in Chinese communities. The Chinese words for "bat" and "luck" sound the same, so water caltrops are supposed to be an auspicious food to eat. The shells become toys for kids old enough to safely handle the spiky pods.

A few Western beliefs regarding T. bicornis have to do with its nickname of "devil pod." Some take that nickname literally and use the nut on altars dedicated to deities with some not-so-nice qualities. Others interpret the shape as protective and use it as a charm to ward off bad influences. Others include the pods in bags that contain mixtures of good-luck items.

The most basic preparation for water caltrops is boiling the seeds in salted water while the shells are still on, for about 25 to 30 minutes. Frustratingly, they'll look exactly the same cooked as they did raw, so you really do need a timer and can't go by visual inspection to ensure they're done. Use a nutcracker to open up the shells to expose the cooked interior. You may find advice online to crack the shells open with your teeth, but a nutcracker is preferable. Eat the cooked caltrop interior by itself, or add it to a stir-fry or to rice.

The taste of the water caltrop can range from something similar to a conventional tree chestnut to a mild yet musky flavor. The texture even when cooked is slightly hard and crumbly, but it's not crunchy like the round water chestnuts you usually find in stir-fries. It's very starchy, and despite the seemingly dry texture, it's got a relatively high moisture content.

Water caltrops can be dried and ground into a flour for use in pancakes and similar preparations, and they can also be candied in sugar. A small market for caltrop jam, caltrop cookies, and other caltrop-containing foods exists in China. The seeds also have non-culinary uses, namely as decorations. You can find garlands made of the shells, and if you search online, the occasional T. natans shell shows up as a pendant.

Water caltrop plants are very good at absorbing pollution in water. While that affects edibility and preparation (more on that in another section), this ability to absorb toxins has an upside; T. natans has been under investigation as a potential tool for removing heavy metals from contaminated water. One study indicated that T. natans removed about 50% of the heavy metals in one lake in India.

Water caltrop seeds are thought to have some medical use, often due to their fiber content. The peels may contain an extract that has potential anti-diabetic effects; one study found this extract normalized blood glucose levels in rats with induced diabetes. In Traditional Chinese Medicine, the peels of the fruits/seeds were thought to be treatments for conditions like diarrhea, and the fruits were considered to be a cleansing food. Ayurvedic uses included treatments for bleeding disorders, edema, sore throats, and urinary infections, among other conditions.

Even though water caltrops grow so quickly in the U.S. that they've been marked as invasive plants, they aren't a huge cash crop. In fact, what is sold here tends to be imported. The water caltrops that have two points are usually available at Chinese markets and other Asian groceries for a couple of months or so in late summer and early autumn. Sometimes, you can find them at farmers markets.

Technically, you could grow your own water caltrop plants if you live outside North America and Australia. If you live in Europe, including the U.K., the plant is considered to be a great addition to gardens. In the U.S., however, the plant's invasive status has landed it on lists of restricted plants in different states. The regulations also differ depending on the specific species; T. natans has more restrictions than T. bicornus, for example. If you're considering growing any of the Trapa-genus plants, check with your state's agricultural department or a local university agricultural extension to see if the plants are prohibited. Even if they're not prohibited, contain them well to ensure they don't escape into local waterways.

Water caltrops are very nutritious despite their small size; they contain several vitamins and minerals, including calcium, iron, and iodine. They've also got a good amount of fiber and contain some protein.

By the way, only the seeds or fruits of water caltrop plants are edible. You wouldn't want to try eating the leaves; they contain glands on their undersides that secrete an acidic substance as a way to deter predators from eating most of the plant. The leaves are also carriers of a parasite called Fasciolopsiasis, and if you become infected, you could experience fever and abdominal symptoms, such as diarrhea and intestinal blockages. The parasite lives on the seeds, too, but boiling the seeds kills the parasite. Never eat the seeds/fruits raw, even though some websites say that this is OK. One more issue with the plant's edibility is its penchant for absorbing toxic metal pollution. Boiling again is necessary to reduce the concentration of toxins in the seeds, but it's unknown how much the toxicity is reduced in other parts of the plant.

Both raw and cooked water caltrops need to be refrigerated or frozen. They have a very short shelf life partly due to their moisture content, and partly due to their attractiveness to insects. The shelled fruits can turn brown, and even drying them isn't enough to make them last much longer.

Freezing the seeds will give them the best chance of staying good to eat for a long time. As long as your freezer is in the proper temperature range (you want the freezer to be at or below 0 degrees Fahrenheit, even though freezing technically starts under 32 F), the seeds should last indefinitely in terms of being safe to eat. Quality is another matter, as foods stored in freezers for a long time become susceptible to freezer burn.

If you prefer to store water caltrops in the refrigerator, store raw, in-shell caltrops in a plastic bag that has some sort of ventilation for up to one week. Cooked and de-shelled caltrops need to be stored in a sealed container, and they'll only last for a couple of days.