Seed of the Week: Water Caltrop

Our bizarre mystery seed from last week was a water caltrop, Trapa bicornis.

The water caltrop (also called horn nut, etc.) is a nondescript little freshwater plant. It is originally from Asia, where it has been cultivated for over 3000 years. Inside the fruit above is one large seed, which can be eaten after it has been boiled. (Some sources say the seed is toxic if not boiled, others say that raw seeds may harbor parasites. Should be cooked in any case. )

If we had known what it was when we got it, we could have put it in our pond or fish tank. Now it is probably too old to grow.

I wonder if the horns help it catch in other plants when it disperses in the water?

Have you ever seen a water caltrop? Do you know this plant by any other names?


  1. Justin

    I found one of these washed up on the shore of Lake Ontario (New York State) in the 1990’s. I took it to my ecology teacher at UNC-Asheville. She was unfamiliar with it. I’m happy to just now find an example.

  2. Roberta


    It is pretty unusual, isn’t it?

  3. Tang, Chi Khay

    Actually, the water caltrop is one of those things that almost all Chinese people know about. One of our festivals, the Mid-Autumn Festival which commemorates various legends, historical events and more importantly, the Autumn Solstice, is celebrated with this water caltrop. The taste is a little similar to yam which is how Chinese parents describe the vegetable to reluctant and picky-eaters. πŸ™‚

  4. Roberta

    Thank you. I always enjoy learning more about this fascinating plant.

  5. Dawn

    I have one of these seeds in among some things left to me by my Grandmother in the 1950s. I always wondered if it was a seed of some type as it rattles if you shake it. Thank you for the information….. Now I will die happy! lol

  6. Hugo

    I have one of these seeds that I bought at the Granville Market in Vancouver in 1997. I’ve never seen another one like this until now, it is one of my weirdest souvenirs and it maybe will be in our family for generations. Thank you for the information.

  7. Temjana

    Wow I never knew what these were called we found them when we were in Taiwan. They are a really interesting looking seed. Thanks for the information. πŸ™‚

  8. emma

    its called singhara in india. i always had them raw as they are much tastier raw than boiled but way better than canned for sure. in india they are mostly consumed raw in early seasons then boiled and during off seasons they are dried and turned into flour and used for several types of sweets.

  9. Roberta

    Thank you for letting us know.

  10. Brooke Pulsinelli

    These are all over the Jersey shore.

  11. Roberta


  12. Ewa

    Thank you! i found it once at Hudson River. I have never seen something like this before. I collected many and brought them back to Poland 20 years ago:) This year i wanted to go back to NYC but hmmm… any greetings!:)) Ewa

  13. Birte

    Years ago I found one on the beach near The Hague in the Netherlands and never knew what it was called. Thank you!

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