“When an orange tree drops its fruit you have to pick it up. Otherwise, as more oranges drop to the ground, the soil will become too acidic for the tree to survive. In the past birds, raccoons, and deer might take up the task of sweeping the forest floor but they don't seem to be up to the job these days. Lots of species will do themselves in if not provided with an antagonist, a mirror twin, a predator. The osage orange (maclura pomifera) has a thick latex flesh surrounding it's seeds. No animal wants this bitter tasting fruit and so the fruit, and seeds with them, rot on the ground. Some think that perhaps the giant ground sloth, in prehistoric times, ate these fruits. Humans killed off the giant ground sloth. So these ghosts of evolution rarely get the opportunity to spread. Without the aid of some hungry animal the circumstances that might lead to new osage orange trees are quite ridiculous. Perhaps the fruit happens to fall into a running stream, the rocks scoring the fruit's tough hide as it bobs along in the current. Then with any luck the fruit becomes lodged in the mud bank of a widening stream. Then the seeds might, just might, decide to sprout."