Oak Apple-gall.

Here is a link that might be useful: oak-apple-gall

Thanks. That's fascinating. It is under a large red oak tree, and could well be red oak, but curiously the plant it is growing on comes out of the ground with just an eight inch stem. So it's not like it's actually on a tree. The tree up above doesn't have any galls. In fact, the tree is just now flowering, and has no leaves at all, but there are several of these plants on the ground nearby without galls with what look like fully formed, and healthy leaves. Do red oak seedlings not go through a flowering stage like the main tree?

In any case, I was getting ready to save the seeds in these pods, but it looks like there aren't any!

Flowering comes with maturity.