Fruit-bearing trees tend to have thorns more often than those that do not produce fruit. This is because the thorns serve as a way for the tree to protect itself. The four tree varieties that have thorns include:
Honeylocusts: Native honeylocust trees have thorns, but those that were developed for landscaping do not feature thorns.
Citrus trees: Like the honeylocust, wild citrus trees have thorns. Though they are not always present, most citrus trees will have thorns at some point in their lives.
Mesquites: Native to the southern region of the U.S., mesquite trees are smaller thorn-bearing plants that can be considered shrubs.
Hawthorns: The thorns on hawthorn trees can reach five inches in length. They are produce both flowers and berries in addition to thorns.