From Foraging Texas:
Prickly Ash trees are found not just in Texas but also worldwide. Here in North America they go by names such as Hercule’s Club, Tickle-Tongue tree, and Toothache tree. It’s very common to see these trees along fence line because ranchers would plant them there because cattle don’t like rubbing against them, so it would protect the fences. In more modern times these trees appear along fences lines thanks to seeds in bird poop.
The leaves and bark of these trees contains a fairly strong anesthetic. Native Americans would cut off one of the thorns and place it on the gum near their hurting tooth. After a few minutes that area would go numb, allowing a friend to yank the bad tooth out. Pioneers and early Texas settlers would use the leaves instead of the bark/spines.