Are those thorns? It looks like something in the pea (legume) family. The leaves/petioles look too thick to be Black locust.

You're in TX, so it's prb'ly some type of warm/hot-climate legume, but that's the best I can offer. Is there something called Texas catsclaw?

Thanks for the input! Yes, the tree does have thorns. However, it is not a cats claw or locust. My husband thought it might be a rattlebox, but it's not that either. The mystery continues!

Could it be Mescalbean Calia secundiflora (formerly Sophora secundiflora)? Not sure if that has thorns on seedlings or not.

Resin

Here is a link that might be useful: {{gwi:324616}}

Nope, it's not the mescal bean (Texas mountain laurel, Calia secundiflora ). That is the plant I originally bought that my mystery plant sprouted up next to, and it's definitely not the same plant. My mystery plant has much larger leaves than mescalbean. Also, mescal bean has no thorns.

Thanks for the input!