Honey Locust
This very common, fast-growing tree is popular in the urban landscape. When young, these trees have an open shape that makes them look like they belong somewhere warmer, like the Serengeti. Mature trees grow tall, with one or two large trunks. Because they do grow so quickly, they're popular street trees, but unfortunately the live-fast-die-young life history of this species doesn't mix well with long-term forestry.
Bark
The bark on a mature honey locust looks like it's made of almost vertical strips several inches wide, with peeling edges. Although firmly affixed, it certainly looks like you could just pull the bark right off the tree. This pattern isn't quite as obvious on a young sapling.
Leaves
This is one of the very few trees we have that have compound leaves. Each leaf is made of many smaller leaflets. In the honey locust, these leaflets are nearly round and very light green. In the fall these leaves turn bright yellow, and the leaflets fall off one by one.
Fruit
Locust trees are known for their long brown fruits. While still unripe, the sticky pulp inside the pods is at its sweetest. (Locusts are members of the bean family. Those big brown fruits are just giant pea pods.) This sweetness is what gives the plant its name. If you never notice locust trees any other time of the year, you are hard-pressed to ignore them in fall, when the pods ripen and drop to the ground.
Thorns
Honey locusts generally have really nasty thorns. Botanically speaking, a thorn is a modified branch. And boy-howdy, are they modified in honey locusts! Often the thorns have thorns! Those branching thorns are one major way of recognizing this tree. There are also thornless cultivars that are widely available, and street trees tend to be of this type.