Tree ID Guide
Each issue of Tree Tuesday includes a general description of the bark, leaves and fruit of the tree so you'll be able to recognize the species in the park, on the street, or deep in the forest while searching for the latest feature tree. Unfortunately, these descriptions are very brief and are not always sufficient for identification, especially if the tree species in question has a look-alike.
This Tree ID Guide gives you the basics on how to identify trees, ideas for learning more about the tree you are identifying, and general tips on how to narrow down the possibilities for an unfamiliar tree. However, if you want to really get serious about tree identification, an official field guide for trees is a critical tool; I would highly recommend Stan Tekiela's Field Guides by state. If you are looking for a good way to identify trees and all other organisms, then definitely check out the awesome website/app Inaturalist!!
Walking Towards a Tree
Be sure to approach quietly so as not to disturb... ok no, trees are notoriously bad at hearing. You can stomp right up to it blasting airhorns and pumping out trap music if you like. But, seriously when you come upon a specimen that is ripe for identification (they all are), it is sometimes difficult to know where to look first. I have often passed by a tree and, taking one look at the leaves, declared that it was an elm tree, only to return later and see that the bark was clearly indicative of a basswood! Hey, it happens to everybody.
Looking at a Tree
Ok, so don't make snap judgments about a tree, but where should I look first? In this whole network of thick branches, flakes of green and stubby stalks, where should I focus my attention? A very general mantra that I go by is "flowers/fruit are fantastic, leaves are less so, bark is bad. " Fruits and flowers are normally the most helpful parts of the tree for identification purposes, this is especially true for conifers, whose fruits can often differ markedly in size, shape, color and texture. Leaves are also helpful and even trees with very similar leaf shapes can be told apart if you look for specific details such as nodes on the petiole, serrations on the leaf margin or trichomes on the underside of the leaf. Relying on leaves can be problematic when leaves from the same individual tree vary greatly amongst each other; some looking like one species, and some another. Although species of birch and aspen bark can standout like a polar bear in the rainforest, identifying the exact species of birch or aspen can remain a struggle. Furthermore, most other trees have grey or brown bark that is often very similar in appearance, making it difficult to correctly identify a tree from bark alone.
In practice, all aspects of a tree should be used as important clues for identification. Depending upon the species, some clues will be more informative than others, but it is usually a good idea to start with fruit/flowers, then leaves and finally bark. The following sections look at each of these components in more detail.
Flowers & Fruit
Flowers can be difficult to see closely since many trees start flowering only when they grow old and tall, putting most flowers out of reach unless you are 14ft tall or skilled at walking on stilts. However, if you do find low-hanging flowers, they can be some of the best tree species indicators. There are two broad types of flowers: imperfect and perfect. Imperfect flowers only have the reproductive organs from one sex: the female pistil, or the male stamen. Thus imperfect flowers may be referred to either as pistilate (female) or stamenate (male). Trees that have only imperfect flowers may sport both female and male flowers, or they may only have one of the two. Perfect flowers on the other hand, contain both the female parts (pistils) and male parts (stamens) in the same flower. Without even looking at the form or color of the flower, knowing if it is perfect or imperfect, and male or female can narrow down the list of possible trees that it could belong to.
Fruit take on such various forms across all trees that it is difficult to draw generalizations that connect them. THIS MAKES THEM MEMORABLE AND PARTICULARLY GOOD IDENTIFICATION CLUES. It pays to notice what the fruits of each tree looks like because even though they may be on the plant for a limited time, they're often littered around the tree - even once the leaves have fallen off (if it's deciduous).
Leaves
Leaves are vastly various; they differ in shape, texture, color, and size to create a plethora of different forms that are often perfectly crafted for specific environments. The leaves of most cacti for instance, have evolved into their signature spines because they lose much less water than a broad leaf with a huge surface area - a necessity in the deserts where cacti grow. In contrast, tropical plants typically have huge leaves to soak up the plentiful sun and don't have to worry about water loss in their rainforest home.
Yet even within the same biome, nature allows for a dramatic range of leaf forms. To better understand this diversity, botanists have created terms to refer to and describe different parts of leaves - check some of these out on the Tree Dictionary page. Here are a couple of basic ideas to start classifying and recognizing the different leaves in your life.
Leaf shape is highly various, but usually trees of the same genus have the same general leaf shape. A couple things to look for in leaf shape are whether the leaf has any lobes or serrations on the edges, and whether it is a compound leaf that is divided into smaller leaflets or if it is just a simple leaf with only one leaf blade that attaches directly to the stem/twig.
Leaves attach to the stem/twig in different patterns, the two most common in trees are opposite and alternate attachments. This pattern is mirrored by the young branches of the tree since branches and twigs grow from buds just above where the leaves form (in the leaf axil).
Texture can vary widely on leaves. Some leaves may have hairless, smooth surfaces, while others might feel waxy, rough or hairy to the touch.
Although this may not always be an obvious place to check, the underside of a leaf can be very informative. For instance, the two species of oak, Bur Oak (Quercus macrocarpa) and White Oak (Quercus alba) have very similar leaves in terms of size, shape, and color, but the Bur Oak has many fine hairs on the underside of its leaves, while the White Oak leaf is hairless. A difference in texture between the topside and the underside of the leaf is common, as is a change in color.
Bark
Upon first glance, tree bark may seem the same on every tree. A second glance might give the same impression. As stated above, bark is generally not a great reference for tree identification. However, some trees do have very conspicuous bark, and others have very distinguishing features if you know what to look for and where to look for them.
The texture of tree bark can vary hugely. For instance, beech trees typically have extremely smooth, grey bark, whereas a number of oak species wear very flat, distinct plates separated by shallow grooves, and other types of trees display peeling, or flaky bark. In addition to the appearance of the bark texture, it is important to observe the physical texture. When you press a finger to the bark is it as hard as rock, or does it feel softer, and slightly spongey? If there are peeling areas of bark, what size are the shreds? Are they thick or thin? Do they bend easily or are they more rigid? Asking these questions may be helpful in distinguishing and remembering the different types of trees around you.
Lenticels are areas of porous tissue in bark that facilitate gas exchange between the inner tissue of the tree, and the atmosphere. Hence, they play an important role in the metabolism of the tree, and can be useful for identification too. On some trees (especially in their youth) the lenticels can be observed as horizontal fissures or scar-like white lines. The lenticels on young paper Birch trees (Betula papyrifera) stand out starkly as white lines against a reddish brown. Lenticels are also present in fruits - they are the white or yellow dots that occur on apples - and are abundant on the roots of mangroves.
Branches may exhibit different bark than that of the main trunk and thus can be helpful in identification. Sometimes branch bark is much smoother than it is on the rest of the tree, but it can also be extra rough and corky, as in the Bur Oak (Quercus macrocarpa) and the Rock Elm (Ulmus thomasii).
Leaf-scars are layers of cork tissue that form over the area where the leaf or leaf petiole was attached before it fell off. They can be found along the length of all twigs, young branches and even the trunk if the tree is young enough. They are generally a different color than the rest of the twig - usually tan or grey which makes them easy to spot. Leaf scars take a unique shape on each tree, this means they are extremely helpful to decide between trees in the same genus that may appear very similar in other characteristics. Fresh leaf scars on the tips of twigs are the easiest to see and often the bundle scars are still visible on them.
Bundle scars represent the location of vascular tissue that flowed through the twig to the leaf and they look like small dots inside the leaf scar. The number and arrangement of bundle scars varies by species, thus adding to the usefulness of leaf-scars as a species-indicator.
There are three types of buds: lateral buds, terminal buds, and flowering buds. The location of lateral buds varies, but on most of the trees I have come across, they arise from the twig above the leaf scars. Terminal buds, which are sometimes called apical buds, only occur at the end on the twig or branch. Flowering buds usually occur at or near the end of twigs, although not always - the Eastern Redbud (Cercis canadensis) sprouts bushels of beautiful flowers along large branches. Buds of all these kinds take various forms and colors depending on tree species, making them an invaluable tool for identification of deciduous trees when they are bare of leaves.
Other Characteristics
A tree will usually grow into a specific form, often referred to as the growing habit of the tree. Growing habits can include forking close to the base to form two main trunks as is common in the Silver Maple (Acer saccharinum), horizontally spreading branches as seen in the White Oak (Quercus alba), and stocky bases supporting many short branches as in many species of Willow (Salix spp.). Of course, these are just a few of the many shapes and sizes that trees can take.
Some tree species are not picky at all about where they live (which is a pretty crazy given they can't leave once they've put roots down) and happily make their home in a variety of soils, climates and plant communities. Other trees are very specific - only settling near rivers for instance or unable to withstand full sunshine, or specializing in a specific soil type. Knowing which trees grow in which environments, not only helps you to identify different tree species, but it also enables you to predict which tree you'll see where.
The area beneath a tree is often a goldmine. Not just any regular goldmine though, a goldmine with tree-parts inside! And no gold!* The fallen leaves, fruit and fruit casings can often give important clues to the identity of the tree, however; it is important to consider that organic matter found beneath a specific tree, may not always have fallen from that individual and could've been attached to neighboring trees instead.
*Tree Tuesday sincerely apologizes for any gold found at the base of tree-trunks. If you find any gold while searching for tree-parts, please e-mail us the location at which the gold was found and we will gladly reimburse you with tree-parts. tree2sday@gmail.com