When identifying trees the first thing most people look for is leaves. Knowing the leaves helps in the warmer months, but many leaves are similar. The first part of identifying a tree by its leaves is as obvious as looking at the shape. Is it ovular, heart-shaped, palm-shaped, or another odd shape? The sugar maple leaf for example is palm-shaped.
The next part to look for is the outside edge or margin of the leaf. Is the edge smooth, saw-like, wavy, etc.? Some leaves have a lobed edge meaning they have “fingers” like the white oak. A few other things to notice are hairs, vein patterns, and thickness. There are simple and compound leaves. Simple means one leaf per stem and compound means multiple leaves per stem. Poison ivy is once compound and has three leaves per stem (leaves identical to box elder). The Kentucky coffee tree is double compound which means there are multiple stems with leaflets branching off the main stem. Pines and firs needles are actually modified leaves and may seem quite similar making it appear difficult. The easiest pine to identify in PA is the eastern white pine because it is the only pine with five needles per group (fascicle). Most pines in PA have needles in groups of twos and threes.
When there are no leaves or they are too far away to see, another distinguishing characteristic is the branching pattern. Do the new young branches shoot out opposite one another, are they in whorls circling the main branch or do they alternate? In Pennsylvania there are few species that have opposite branching. One acronym to help when identifying opposite branching trees is MAD Horse. All Maple, Ash, Dogwood, and Horse chestnut trees have opposite branching. Every plant in the honeysuckle family is also opposite branching. With close to 200 tree species in PA this helps narrow things down. Another distinguishing part of branches to look for is the leaf scars and new buds. A leaf scar is the area on the twig where a leaf attaches. Removing the leaf reveals a “scar.” Scars on a black walnut look like a monkey face with buds being fuzzy and white. The center (pith) of different species can also aid in tree identification. If the young twig of a walnut is sliced open the chambered pith looks like a filter. For stag horn sumac the twigs are hollow like a straw.
One of the first things I look at myself is the bark. If the tree is too young to see a pattern I look for color. With red maple the bark pattern is variable so color and branching pattern helps. One cool fact about shagbark hickory is that bats can live under the bark.
A few other characteristics include but are not limited to flowers, fruit, location, and fungi. Some trees require full sun or shade. Others require wet lowland soil near streams or ponds. There are also different species of fungi that only grow on one type of tree. The cracked cap polypore only grows on black locust for example. A dichotomous key may also help with identification.