My Neighbor Gave Me a Bag of These Strange Black “Nuts” — What Are They, and How Are You Supposed to Eat Them?

At first glance, the objects in this photograph hardly look like something you would put on a dinner table.

They are dark, hard, wrinkled, and covered with unusual curved points that make them look almost like tiny animal horns. If someone handed you a bag full of them without explanation, it would be completely understandable to wonder:

“What exactly are these things—and are they even edible?”

Based on their distinctive shape and appearance, these are likely water caltrops, also known in different places as water chestnuts, buffalo nuts, devil nuts, or horned nuts. They belong to the Trapa group of aquatic plants and have been eaten in parts of Asia for centuries.

However, because several dried seeds and plant materials can look surprisingly similar, you should not eat an unidentified specimen solely because it resembles the ones in this photograph. The exact species and source should be confirmed first.

What Are Water Caltrops?

Water caltrops are the fruits of aquatic plants that grow in freshwater environments.

Unlike the familiar water chestnut sold in cans at grocery stores, these are a completely different plant.

The fruits develop underwater and form hard, woody shells with characteristic horns or projections. When mature, they can become very dark—almost black—and their unusual shape gives them their memorable appearance.

In some cultures, they have been collected as a seasonal food and prepared in traditional dishes.

The hard outer shell protects the edible seed inside.

That means you don't simply bite into the outside shell like a conventional nut.

Why Do They Look So Strange?

The unusual horns are not just for appearance.

The fruit's shape helps the plant reproduce. Once the mature fruit separates from the plant, its structure can help it settle in aquatic environments and eventually produce a new plant.

Different Trapa species can produce fruits with different numbers and arrangements of horns.

Some have two prominent projections, while others can have more complicated shapes.