It sounds like your neighbor gave you a bag of mâcres nageantes, which are edible aquatic plant seeds also known in English as water caltrop or water chestnut (from the species Trapa natans) — not seaweed or a random plant.
Here’s what you need to know:
🏞️ What mâcres nageantes Are
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The mâcre nageante is an aquatic plant that grows in still freshwater such as lakes and ponds.
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Its hard, nut‑like fruits have distinctive horned shapes — which is why people sometimes call them “devil’s horns” or “water chestnuts.”
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The edible part is the seed inside the hard shell, which is rich in starch.
🍴 Are They Edible?
Yes — the seeds of mâcre nageante are eaten in several parts of the world, especially in Asia where they have been cultivated and consumed for centuries.
In China, for example, these seeds are traditionally:
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Boiled
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Roasted/grilled
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Eaten as a snack or cooked
They are sometimes sold already cooked and ready to eat in markets.
