What On Earth is This?

So, I've got this mystery plant growing in my garden. I certainly don't remember getting this from the nursery, of course, I may be mistaken. It looks to be a mini-tree and has large leaves. At the bottom, the stalk is about as wide as a broomstick and a half. Here's a close-up view of the spiky thingy in the "Y" sections:

A bit larger than a walnut, and on the hard side. Although the spikes aren't that prickly. What could this be? A giant weed? Not likely. Something that a bird dropped down and took root?

In other news, Icarus Shawl is progressing, very slowly. I just haven't felt up to much knitting due to the heat and humidity. Usually, I love the heat, but now it's August and together with being a little stressed out over the job situation, I'm kinda tired.