Other seeds, fruits, and plant structures can sometimes look similar.
And when food safety is involved, “probably” isn't good enough.
If there is any uncertainty, don't taste one to see what happens.
Identification should come first.
The Fascinating History Behind These Strange Fruits
One reason water caltrops are so interesting is that they demonstrate how different traditional food cultures can be.
A food that looks bizarre to one person may be a familiar seasonal ingredient to someone else.
For generations, communities in parts of Asia have harvested aquatic plants and incorporated their edible seeds into local diets.
The hard, horned exterior may look intimidating, but underneath it is a starchy seed that can be prepared as food when the correct species is used.
That is part of what makes traditional foods so fascinating: appearance doesn't always tell you how a plant has been used historically.
The Bottom Line
The strange black fruits in the photograph appear consistent with dried water caltrops (Trapa species), sometimes called buffalo nuts, devil nuts, or horned water chestnuts.
They are traditionally eaten in some parts of the world, with the inner seed being the edible portion after the hard outer shell is removed.
But don't rush to crack one open and eat it just because it looks like the photograph.
Confirm the exact identity and food safety first, particularly if the fruits were wild-collected or came from an unknown source.
If they really are edible water caltrops, they can be cooked and the starchy seed removed from the hard shell.
And that's the fun part about unusual foods like these: what initially looks like a strange black object with horns may actually be a traditional food that has been enjoyed for generations.
Just make sure you know exactly what you've got before taking that first bite.