The genus Acer, commonly known as maple, contains over 120 species of trees widespread throughout the Northern Hemisphere. Maples are significant for their prized wood, their ecological role, and the sap used to produce maple syrup. They are also popular ornamental trees, celebrated for their vibrant fall foliage. Accurate identification requires focusing on the distinct characteristics of the leaves, bark, and seeds.
Leaf Structure and Arrangement
Maple leaves are easily recognized by their unique structure and arrangement on the twig. The leaf arrangement is consistently opposite, meaning two leaves grow directly across from each other at the same point on a stem. This opposite branching pattern is a major identification cue, as most other common deciduous trees have an alternate arrangement.
The typical maple leaf shape is simple and palmate, resembling the palm of a hand with several finger-like projections called lobes. These lobes radiate outward from a central point where the leaf stem attaches. The indentations between the lobes are known as sinuses, and the shape and depth of these sinuses are crucial for species differentiation.
The Sugar Maple (Acer saccharum) displays five lobes separated by rounded, U-shaped sinuses and has a smooth leaf margin. The Red Maple (Acer rubrum) has three to five lobes, but the sinuses are shallower and more V-shaped, with saw-like serrations on the edges. The Silver Maple (Acer saccharinum) is characterized by deeply cut leaves with five narrow lobes and sinuses that extend almost to the midrib. A notable exception is the Boxelder (Acer negundo), which has a compound leaf structure with three to five separate leaflets on a central stalk.
Bark and Twig Characteristics
Observing the bark and twigs provides year-round identification clues, especially when the trees have shed their leaves. Young maple bark is thin and smooth, often gray or reddish-brown, and may feature small, pale lenticels (pores used for gas exchange). As the tree matures, the bark texture changes significantly, developing species-specific patterns.
The bark of a mature Sugar Maple becomes deeply furrowed with long, irregular ridges that may peel away from the trunk in vertical strips. Silver Maple bark matures into a shaggy, gray surface with long, loose strips that peel away at the ends. The Red Maple’s bark is smooth and gray on young trees, developing into shallow, scaly ridges and plates on older specimens.
Twig characteristics, particularly the arrangement and appearance of the winter buds, offer a reliable method for winter identification. In maples, the terminal and lateral buds are arranged oppositely, mirroring the leaf pattern, with the terminal bud usually larger. Sugar Maple twigs are slender and reddish-brown with sharp, pointed terminal buds that are brown and scaly. In contrast, Red Maple twigs are reddish and feature blunt, rounded buds that are distinctly red.
Identifying Samaras
The fruit of all maples is a distinctive structure known as a samara, commonly called a “helicopter” or “key,” which consists of a winged seed joined in pairs. This paired, winged fruit is unique to the genus Acer and is a reliable feature for identification. The papery wing allows the seed to spin as it falls, aiding in wind dispersal. The angle at which the two wings join is a primary species differentiator. For instance, Norway Maple samaras spread at a nearly 180-degree angle, while Sugar Maple samaras join at an acute V-shape (50 to 60 degrees), and Silver Maple samaras are the largest, spreading widely (60 to 100 degrees).
Distinguishing Common Maple Species
Combining these features allows for the separation of the most common maple species. The Sugar Maple is identified by its five-lobed leaves with smooth edges and rounded sinuses, paired with mature bark that is deeply furrowed into vertical ridges. Its samaras have an acute V-angle, and its buds are sharp and pointy.
The Red Maple is recognized by its three to five lobes with shallow, V-shaped sinuses and serrated leaf margins. Its twigs and blunt buds are often reddish, and the mature bark is gray with scaly plates. Red Maple samaras have a narrow angle, less than 70 degrees.
The Silver Maple stands out with leaves that are deeply cut, nearly to the central vein, and have a silvery-white underside. The mature bark is shaggy and peeling, and its large samaras spread at a wide angle.
The non-native Norway Maple is distinguished by its leaves, which look similar to Sugar Maple but have a milky white sap that exudes from the petiole when broken. Its defining samara feature is the nearly flat, 180-degree angle between the wings.