what kind of tree has the fruit or nuts that look like green tennis balls?

If they look like giant green tennis balls (big as softball or grapefruit) that is an Osage Orange. It has other names like hedge apple and osage apple. It is wrinkly on the outside like a brain when ripe.

As a few others have said, it's an Osage orange. A few years ago, my daughter and I noticed what looked like dozens of tennis balls laying below some trees. We picked one up and went on a quest to find out what it was. One of the teachers at her school identified it, so we were able to look up more about it on the internet. My daughter wound up doing a presentation for her class, and they cut it apart to see what the inside looked like. Quite the educational experience!

From what I've read, squirrels really like the fruits, and the trees themselves can be planted side by side to make a thorny hedge.

Sounds like a Walnut, crack open the green tennis ball and there will be a brown one inside, in that is the meat of the walnut. If I'm correct.

It could be a walnut tree but the walnuts are smaller than tennis balls

Maybe a lime tree or bush but the limes are a different shade of green......maybe you could cross lemons and limes and come out with the correct color fruit!!!

In southwestern Pennsylvania, they're commonly called "monkey balls," but in other regions, this peculiar fruit and the trees from which they fall are known as hedge apples, bowwood, bois d'arc (French for "wood of the bow"), bodark, geelhout, mock orange, horse apple, naranjo chino, wild orange and yellow-wood.

The tree's official name is Osage orange.

You mean lime greenish in color and look kinda wrinkly? That would come from an Osage orange tree. It is a very old type of tree and I have only seen them in Ohio and PA. My Gram used to use them like deodorizers....I don't believe you can eat them at all....

They come from the Bois D' Arc tree in Texas. We also call them horse apples.

Black walnuts are smaller than tennis balls and hedge apples (Osage Orange) are larger so I dont know which you have.

American walnuts look like that before they turn brown and fall, the nut is inside the "ball"

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