This looks like a young Black Locust, either a seedling or a sucker (growth arising from a root on a nearby tree). Suckers can be challenging to remove, but seedings should be easier. The most immediate removal method is to either dig/pull it up (careful of the thorns on the stems) or cut it down. If it's a seedling, it may only need to be cut down a couple times before it dies out. If a sucker, this won't work as well, but you can still try. Using a herbicide will work if it's a seedling, but won't work well if it's a sucker. Do you think there's a mature Black Locust tree nearby? Arborists sometimes can apply chemicals to a tree that can suppress suckering, but otherwise, using a herbicide risks harming the parent tree, which is also risky to try if it's not on your property. Several species of tree sucker naturally, but tend to do so more when they are stressed or when roots were damaged (like being cut by construction or utility work).

If this is a sucker and you cannot (or do not want to) use herbicide or other chemicals, then the only recourse is to keep cutting it down as often as it reappears. Eventually, hopefully, it will stop returning, but that may depend on how large of a root it is attached to, and if that root is healthy and vigorous or in decline for other reasons.

If this is a seedling that you cannot dig up (due to how it's wedged into the stone area), then repeated cutting back of all growth each time it reappears will starve-out the seedling's roots, and it will eventually stop growing back. How long this process takes is hard to guess, but based on how young the plant appears to be, it might only take a few weeks.

Miri

That is a runner from the Maryland native tree
called Robinia pseudocacia, also known as Black Locust, or some may even mistakenly call it Acacia.
It has fragrant droops of flowers in the spring and we'd expect that you either have a mature one somewhere nearby or that someone removed one, which can encourage these suckers/running roots to pop up as the tree tries to spread.

You can try to dig it out, cut it repeatedly or cut it and apply a dab of non-selective, systemic weed killer with the active ingredient glyphosate (though this may need to be repeated at intervals as well. Follow all label instructions carefully.)


Christine

You're welcome!