The "Trees of North America" guide states that birch trees feature alternate leaves, with one leaf bud positioned at each growing node. All birch tree species in the United States lose their leaves each year. Various aspects of a birch leaf can allow you to figure out which type of birch tree it is from and its size, shape, color and other features.
Study the size of birch leaves, which typically are not large. Measuring birch leaves can allow you to ascertain what kinds they are. For example, the leaves of a paper birch are just 2 to 3 inches long and only about 2 inches wide. Some of the larger birch leaves belong to sweet birch and yellow birch, being 5 and 4 1/2 inches long, respectively. Smaller birch leaves include those found on a Yukon birch, which rarely exceed lengths over 1.5 inches.
Inspect the shape of birch leaves. Some birch leaves, according to the "National Audubon Society Field Guide to Trees," are elliptical and have a very short point and a rounded base. Yellow birch and sweet birch leaves fall into this category. Others, like the leaves on gray birch and European white birch, are triangular. Some birch leaves have an oval but irregular look, like the foliage on a river birch.
Examine the network of veins on a birch tree's leaves. Birches have a specific number of veins on their leaves. The yellow birch possesses leaves with as few as nine and as many as 11 veins on the both sides of the leaf, with the veins having a hairy texture. River birch has seven to nine veins on each side of its leaves, while the leaves on a water birch have only four or five veins on each side. Paper birch has five to nine veins, and gray birch has from four to eight on its leaves.
Observe the colors of birch leaves in both summer and fall. While green is the predominant color during the warm summer weeks, birch leaves will be different shades of green. For instance, a yellow birch has a dark but dulled tint of green on the top of the leaf and a greenish-yellow hue to the undersides. Shiny green above describes a river birch's foliage, but the underneath side of the leaf has a whitish look. In the fall, most birch trees change to a shade of yellow. Some, like sweet birch and yellow birch, become bright yellow, while others, such as river birch, change to a much duller type of yellow.
Check the other features of birch leaves to identify them. Consider any aromas they may give off when you crush them. This applies in particular to sweet birch and yellow birch, which grow leaves that have a wintergreen scent. Carefully examine the leaf edges, looking for differences in the teeth, or serrations. The sweet birch has single teeth along the edges, but the serrations on a gray birch are double-toothed along the borders.