These grow like weeds around here. I’m about to harvest 4 of them from various locations. Don’t care that it’s not spring because, well, they’re everywhere and I’m curious lol. Really it’s because I’ve spotted them in parking lots and don’t want them to be weeded out.
In my dreams these are cork bark elms. I just want them to be some kind of elm. 
They look like elms to me. What is your location, might help narrow it down.
Best,
Dan
Figured they were elms 
I’m in Charleston, SC.
Could it be hornbeam?
Elm is more likely than hornbeam. Hornbeam leaves are a bit more pronounced with the ridges.
One easier way to tell is to look around at the surrounding trees.
Yeah, thought of that, but didn’t spot anything too obvious. I didn’t look hard though. I spent more time scoping out the area trying to figure out how I’m not going to look like a weirdo when I grab them haha…
Technically, you’re weeding someone else’s garden. When you’re done there, I have plenty of acer rubrum you can come collect. I don’t even have to be home.
Lol, I’ve got a ton of those as well. I’m thinking of starting some whips next year for an eventual forest planting. At this rate they’re gonna forest themselves though.
Those look like Siberian Elm to me, less desirable for bonsai than American Elm, but they grow like weeds (invasively) everywhere, so great cheap material!
Hmm, well, my standards are pretty low with bonsai. Will it live? Yes? Lemme make some room over here. 
Same here, I collected one just the other day! I think they tend to drop branches very easily, the solution being managing their growth very closely. I think there was a stream on Zelkova where Ryan talks at length about trees that act like this, birch, elm, willow, etc. Apparently if some strong branches are allowed to run wild the tree naturally just drops other weaker branches, but if you control the growth of the stronger branches you reduce this risk significantly.
Well, I collected them. Even though they were small they were deep. Way deep. I think I killed them lol. 
They were destined to be weeded out anyway, so I’m not too sad about it, but I would have preferred to not do too much harm. I collected them last Wednesday. Four days later and the leaves have completely turned brown on two of them and slowly turned brown on the biggest of the three. I’ll give them a few weeks to see if they’ll push new growth, but I’m not optimistic. All is not lost though. I’ve also harvested some native maples from around the yard and put them in the same pond basket that I put these mystery trees in. Mystery because now I’m wondering if they’re hornbeam. 
I’ve had success with these in the past, so hopefully this goes well.
Double-serrate leaf = elm. On the plus side, they germinate easily and will get to the size of those you collected in a year or two
Ah, cool. I actually have two that are tag-alongs in a couple of nursery plants I’ve acquired this year. I plan on harvesting those in the repot next year, so another reason why I’m not too broken up over it.
I got a blue spruce and ponderosa the same way 
Looks like a cedar elm: alternating leaves, blunt tip, leaf symmetry. American elm have an asymetric leaf and more pointed tip. Either make great bonsai.
I assume you live in the south (pictured with crepe myrtle) so doubt it is a Siberian or Chinese elm unless you planted it.
