Osage oranges are probably the most interesting thing I saw in the ~ 1,000 miles I've driven so far this week (that and that Hokies *really* like to decorate their cars).
The lime-green, softball-sized fruit littered the ground along backroads (particularly in West Virginia), where these normally nondescript trees grow in crowded rows of rusty, cluttered branches. These trees were commonly planted as thorny hedgerows in the 1800s, prior to the invention of barbed wire. Maybe the trees I saw were the remnants of old fences.
It's been hypothesized that the fruit of this tree were once dispersed by extinct North American ground sloth, elephant or horse species. There are a few giant fruit species that appear to have lost their co-evolved animal disperser (e.g. avocado, prickly pear and papaya). These marooned plants are sometimes referred to as "anachronisms." There's pretty good evidence that ground sloths were the natural disperser of Joshua trees in the American Southwest. Their extinction is leaving these plants in the lurch as climate change slowly moves their habitat away.
Native to Texas, Osage orange was one of the species planted throughout the Midwest and Great Plains by the U.S. government during the Great Depression to improve the environment and give the unemployed something to do. One of my friends once told me that tons of (now very large) walnut trees remain on marginal land in Indiana. I guess most people have forgot about them, but their high quality wood is ripe for harvest.
The twisted old Osage orange in my parents' yard finally keeled over this fall. Half the root system was dead but the thing still appeared to be alive when it began to shed its leaves a few weeks later. My siblings and I had some fun trying to cut into one of its fruits when we were young. Those things are impossibly sticky. I remember it took us about an hour to work our way into it with one of my mom's kitchen knives, which she was then forced to throw out.
My parents have been losing a lot of the old trees that I grew up with. According to their arborist, their soil has too many boulders to allow the trees adequate purchase. Tulip trees are springing up in place of a lot of non-natives, which is a pretty good trade. A couple old walnuts, a Paulownia and a massive cherry (the largest I've ever seen, ~4' dbh*) are on their slow way out. Good specimens of these species can be worth thousands of dollars in lumber and veneer wood. I've been egging my parents into trying to sell them before they completely collapse, but they're no doubt too gnarled and heartrotted to be worth anything.
A quick Google search suggests that no one has any interest in harvesting yard trees anyway. In addition to poor dimensions, urban trees are often filled with old nails, screws and fence wire - which may have become invisibly entombed a hundred years ago, but can kill when the mill saw encounters them.
*dbh = diameter at breast height (a standard forestry metric)