SearchResearch Challenge (8/18/21): What are those things on the ground that hurt my feet?

That tree... 

The canopy of the mighty oak

...in the back yard is, I was told by the arborist, a black oak.  

It’s certainly an oak—it rains acorns in the fall, loses all of its oak-shaped leaves, and is tall and massive—it’s a lovely paradigmatic example of an oak.  The arborist who tended to it when it was still a sapling told me it was Quercus velutina, a black oak.  

This morning was cool and overcast, perfect for walking around in the backyard under that oak tree with the picture-perfect spreading limbs.  Ah.. the verdant life!  

Except that when walking around in bare feet, there are lots of acorns and zillions of small, very hard, nubby things that feel like Lego blocks underfoot.  It's a beautiful tree, but it also sheds a ton of things that are painful to step on without shoes.  

To say that I’m curious about many things is probably an understatement.  So of course through my pain I immediately wondered, “What are those things?”   

This is what the yard looks like up close:  

 

You can see a few leaves, an acorn, the cap of an acorn, and lots of those small brown knurled balls, each about 6mm (about 1/4 inch).  I don't know what they are, so I'll call them nubbins until I figure out what they actually are. They’re everywhere.  But what are they?  

I plucked a small stem with a few leaves, an acorn, and a couple of the mysterious nubbins.  Here you see a typical branch end:  

And a bit of a closeup so you can see the objects of interest... 

The nubbins attach to the stem just above the acorn.  Here you can see two of them, but often there will be 1, 2, 3 or 4 nubs.  (Never more than that.)  

And here’s a photo with everything taken apart: 

I spent a little time SearchResearching this one--and finally figured it out.  I won’t tell you all the ins-and-outs of my search, until next week.  

Afterwards, I also realized that the pain in the soles of my feet would make for a great SRS Challenge for the week.  While doing this I learned a good deal about how to search.  Can you answer these Challenges? And what can you learn in the process?  

1. What are those nubbin things?  Is there a name for them?  

2. What do they do for the tree?  Why would a single tree generate so many of them?  (I estimated, using Fermi estimation) that this tree produces around 100,000 of these per year.  So over the past 10 years, that's a cool 1 million nubbins (or whatever they are).  What's the point from the tree's perspective? 

Can you figure it out?  If so, let us know what you did to get to the answer.  

Search on!  (Botanically!)