This is the Osage Orange tree, scientific name Maclura pomifera. This tree and many others like it grows in a city park in St. Louis, Missouri. A friend and I were walking in the park and noticed the very distinct fruit of this tree, called Horse Apples. I grew up in the Mid-South and I remember these trees from my youth, but he grew up in north part of the Mid-west and he does not. This tree, a native species of the United States, does have a limited geographic range or distribution and is common in the Great Plains region.
Some Osage Orange trees bear fruit and some do not. The trees that bear fruit are female. Judging by how successful these trees are there must be some male trees nearby but I do not did not photograph any. I depend on distinct characteristics to help me identify plants and trees. I only took pictures of females because the fruit helps me to easily identify this species.
The fruit is large and heavy. As you can see here, about the size of a soft-ball.
Inside are the seeds and they look a lot like sunflower seeds to me. The fruit smells like oranges, and squirrels and other forest animals don't readily eat them. However farm animals like Horse, of course and cattle have been known to eat them. That's where the common names come from.
Finally check out my video, which also happens to be my very first attempt at a Video Blog.