Leaves are one of the most conspicuous parts of a tree—and each tree has a certain number of leaves at maturity. For example, a maple tree (genus Acer) with a trunk around 3 feet (1 meter) in diameter will have about 100,000 leaves in a good summer (that means no drought conditions or defoliation of trees from creatures like gypsy moths). An oak (genus Quercus) will have about 700,000 leaves, while an American elm (Ulmus americana) can have more than five million leaves in one season.