What Tree has round green fruit not apples?
Here in Kansas we have a alien tree species called hedge apple or osage orange. The fruit is about the size of a grapefruit with a rough pebbly surface that stays green. It is NOT edible even though it is related to oranges and is in fact a kind of citrus. I have also heard it called trifoliate orange. When young the seedlings have 3″ long, sharp thorns that makes it useful for planted hedges that will restrict livestock and trespassers.