Birches can be found primarily in the cooler parts of the Northern Hemisphere. Approximately 100 species of trees and shrubs are in the Birch family (Betulaceae), and 40 known species of birches (Betula). Birches have been used for many things: its wood for cabinet making, or the bark for basket weaving. Identifying birch trees by their leaves is one major way to tell them apart.
Paper Birch (Betula Papyrifera)
Paper birch are the most widely spread species of birch tree, spanning the entire width of the northern United States, and the entire width of Canada into Alaska, except for the high Arctic.
Besides its paper-like bark that sheds in sheets--which can actually be used in a similar manner to parchment--you may identify it by the oval to ovate leaves. They grow 2-3 inches long and 1 1/2 to 2 inches wide. They have a round base, pointed tip, and double-toothed margins.
The river birch (Betula nigra) is found in an irregular range along the East Coast from Massachusetts to South Carolina and into the Midwest. Older trunks develop a grey-black, scaly coloring. It is also commonly found along streams and is likely to be the birch you have found if you're in a low elevation of the southern United States.
The leaves are irregularly oval and grow 1 1/2 to 3 inches long and 1-2 inches wide. They have coarse, double-toothed margins and are hairy on the stems and underside of the stout midrib.
Not to be confused with the river birch, the water birch (Betula occidentalis) is a smaller tree, growing 20-25 feet tall versus the standard 80-foot height of the paper and river birches. It is found in western and Pacific northwestern states and into parts of Alberta, Canada and British Columbia.
The water birch forms often impenetrable thickets around streams, which is where it gets its name. The leaves are very similar in shape to the paper birch but are smaller. They are not as slender looking as a paper birch leaf. They grow 1-2 inches long and 3/4 inches to 1 inch wide. The branches sometimes open into a crown and droop.
The yellow birch (Betula alleghaniensis) can often be mistaken for the paper birch to the untrained eye. The leaves are similar, but longer and narrower, which perhaps mimics the structure of the entire tree in comparison. The leaves grow 3 - 4 1/2 inches long and 1 1/2 - 2 inches wide. At the base, they are rounded and heart-shaped.
The stems of the leaves can be slightly hairy or fuzzy, and there are tufts of fine hairs in axils of veins on the undersides. The cones (called strobles) that are found on the ends of branches right along the leaves are ovoid, erect, and shed their scales slowly in comparison to the paper birch cones, which are more cylindrical and shed fast).
Known by many for its strong wintergreen scent and flavor when the twigs are stripped apart, the sweet birch (Betula lenta) also known as the Black Birch or Cherry Birch, grows to about 60 feet tall and has bark that doesn’t peel. Its leaves are ovate to oblong in shape and grow 2 1/2 - 5 inches long and 1 1/2 to 2 inches wide. The leaves have a tapered apex, commonly a heart-shaped base and a single tooth margin. The stems are hairy.
The leaves of the gray birch (Betula populifolia) are the most distinct of all the birch species here mentioned. They are triangular in shape and grow 2 1/2 to 3 1/2 inches long and have coarse double tooth margins. The bark looks very similar in color and texture to paper birch but it doesn’t peel. They grow to be about 30 feet tall and in a very small region compared to other birches, in the northeastern United States from the New Jersey area up into Newfoundland, Canada.