"Why do oranges grow on orange trees?"

Joshua and I have game time most every day. We play board games or just read a book or two. Today we played Hi Ho! Cherry-O. The old version of the game you pick cherries off of cherry trees. The version we have you pick cherries off of cherry trees (red leaves), oranges off of orange trees (orange leaves), apples off of apple trees (green leaves), and blueberries off of blueberry trees (purple leaves).
Joshua decided he wanted to pick oranges. As we played the game he asked, "Mom, why do oranges grow on orange trees?" I said, "Oranges don't grow on orange trees. They grow on trees with green leaves. The leaves are green due to a process called photosynthesis (if I remember earth science at all)." He then proceeds to say, "Well, isn't that interesting!" I think I have a scientist in the making, or he is already learning how to stop a conversation...lol!