What tree is this?
This is known botanically as Poncirus trifoliate, or Hardy orange. The fruit are edible, but not palatable. They are very seedy and extremely tart. It is not a very commonly used landscape plant, though it is seen on occasion throughout the southern U.S. The plant is most notable for its large thorns and as such it has often been used as a hedge plant. One can imagine it would be quite successful at keeping unwanted visitors away. Occasionally used as a single specimen due to its uniqueness, but small white flowers provide limited ornamental value. Fall foliage color is yellow, but not spectacular. Most value comes from the fact that it has unusual growth habit and distinct appearance.