Some subtle differences and obvious disparities occur among the leaves of the 13 separate species of native maples (Acer) in North America. Keying on these distinctions can help you identify to which species the leaves belong.
The portions of a leaf that extend outward, resembling fingers, are the lobes of the leaf. On maples, certain species will have a specific number of lobes on the leaves, making identification possible. For example, the black maple (Acer nigrum) typically has three lobes on each leaf, while the silver maple (Acer saccharinum) has five lobes.
The indented area that exists between leaf lobes is the sinus. Maple leaf sinuses vary, with some going deep into the centre of the leaf, such as those of the silver maple. Other sinuses are not as deep, with this a feature on species including the striped maple (Acer pensylvanicum) and the mountain maple (Acer spicatum).
The size of the maple leaf is another aspect of the leaf that helps to identify it. Bigleaf maple (Acer macrophyllum) foliage lives up to its name, with diameters up to a foot, while other maples, including red maple (Acer rubrum) and sugar maple (Acer saccharum), are in the range of 3 to 6 inches across, according to "Trees of North America."
The colour of a maple leaf is another determining factor in its identification. Silver maple, for example, will be a light green shade above, but its undersides will appear a silvery-white mixture. The edges of a maple leaf can help you identify it. Look for serrations, such as the sharp teeth along the margins of a sugar maple leaf.