Any elms in the area?

Elms produce alternately arranged leaves.

Yes, there are definitely Elms in the area. Unfortunately I took this guy from a crack in the sidewalk from a neighborhood where I was just on a walk. I'm now far from there, so I can't easily go look, but I know Elms are common here in Denver.

Are Elms good trees to plant in your yard - Someone once told me they are "weedy." Is this true, what does it actually mean, and will I regret in 20 years if I plant it?

Plant asked about is not an Elm.

I understand what you mean about alternating leaves on the Elm, but when they are seedlings they may look different - no?

Doing some more research --- my seedling looked EXACTLY like this a few months ago. Chinese Elm

Maybe the potted one isn't actually producing truly paired leaves, the way to check is to look real close. If it is Ulmus parvifolia that is a nice garden tree that is even used for bonsai. This species has been confused in cultivation with the comparatively mediocre U. pumila which I wouldn't plant myself.