What kind of fruit is this?

Asked August 26, 2017, 1:57 PM EDT

Found this on the ground under a mix of beech, oak, and some other unidentified trees. It's firm but not hard, easy to cut, no husk, a little over an inch in diameter. Others had similar external markings but were closer to brown or green. Thanks!

Montgomery County Maryland

1 Response

We recently got another question about this and agree that this looks like a fruit of some sort but it isn't!
It is actually a type of gall that oaks can get. There are many, many types of galls. Galls are harmless abnormal tissue swellings which can be caused by insects, in this case a small cynipid wasp.
Here is a page about galls: https://extension.umd.edu/hgic/shade-tree-galls

This one looks like the aptly named 'plum gall'.
There is nothing you need to do.