It’s easy to go through life with what our third-grade teacher taught us about trees. What we ‘half remember’ is enough for us to happily relegate trees to the background of everywhere we go and everything we do.
It isn’t until something – or someone – gets us to look at a specific tree, or knowingly spouts the name of a tree because of its leaf shape, that we take a closer look and start to marvel at the diversity of shapes, leaves, branching or barks. Then we want to know more.
First, What Exactly is a Tree?
Sounds obvious, but officially it’s a woody plant with a single vertical trunk that measures a minimum of 3 inches in “Diameter at Breast Height” (DBH).
What is not a tree?
A shrub or bush, on the other hand, is a woody plant that grows low and has multiple stems. No trunk.
- A vine, also a woody plant, cannot stand on its own but needs to support itself on something. Again, no trunk.
- And a palm is not woody.
What Are the Parts of a Tree?
To move forward, we need to know the main parts of a tree:
The cones or flowers that serve as reproductive mechanisms, so the species don’t die off.
- The central column or trunk, which is covered with bark.
- The distinctive leaves that grow out of the branches and form the green crown.
- The network of roots that anchor the trunk into the ground.
- The branches and twigs that grow out of the trunk, above ground, in different configurations.
Species? What is a tree species?
Species? What is a tree species? It’s “an individual kind of tree that shares the same general appearance and the same characteristics of bark, leaf, flower, and seed.”
Nearly 1,200 species of trees grow naturally in the U.S. To that we can add all the trees that people have brought here from elsewhere and planted where conditions are similar enough for the trees to thrive.
(That accounts for hundreds of more species of ‘naturalized exotics.’) All told, worldwide we have about 50,000 species. With that many species, we’d better have a good way to name them.
How Do We Name Trees?
We refer to trees by a double name, made up of their genus and species. A species is the most specific level of classifying living things. A genus brings together a group of closely related species.
How Plants are Named
- Uses Latin Names:Example-Red MapleFamily:Aceraceae
- Class:AngiospermaeVariety or cultivar:October Glory
Scientific Name is usually listed as
Let’s see how this works, with an example:
We’ll start with an oak tree, a tree most of us have seen since oaks are found in so many climates throughout the United States. All 60+ species of oaks fall under one single genus:
But how can we tell what particular species of Quercus we’re examining? The species of oak can usually be identified by the shape of the leaf. For example:
A Southern Red Oak, or Quercus falcata, has a long narrow lobe at the end of the leaf, plus one more on either side, that makes it look a bit like a turkey foot. (“Falcata” is actually the name of a pre-Roman sword. Can you see that in the leaf?)
In California, however, we are likely to see a Valley Oak, or Roble, which goes by the genus and species of Quercus lobata. The “lobata” name comes from its easily identifiable, deeply ‘lobed’ leaves. (Think earlobes.)
Two Basic Tree Types: Conifers and Broadleaf Trees
Trees can be divided into two easily recognizable groups: conifers and broadleaf trees. The name conifer comes from the cones that grow on these trees as their form of ‘fruit.’
of conifers in North America, pines, redwoods, firs, spruces, larches, cypress and cedars are the most familiar ones. Most have some form of a needle in the place of flat leaves.
(On the other hand, broadleaf trees have exactly that: leaves that are generally broad and flat, even though they come in all shapes and sizes.)
A Side Note
Evergreen or Deciduous?
Before we start examining conifers and broadleaf trees any further, let’s clear up a mistake people often make. Trees that do not lose their leaves each year are called ‘evergreen.’ Those that lose them are called ‘deciduous.’
We think of all conifers as staying green all year – think pine trees, like Christmas trees – and all trees with leaves as losing them. But that’s not always the case.
Let’s start our examination of conifers first, as they’re a little less complicated to identify than broadleaf trees.
As we said, these
trees get their
cones as part of their
(The two exceptions to
that rule are yews
and junipers that
fruit instead of typical
cones, but still qualify
as conifers for their
Conifers have either needles or scales, instead of traditional leaves.
Needles are long, thin and pointy (remember the Christmas tree?). In the case of needles, the growth pattern and shape of the needle may be your identifier.
- If the needles grow in little bundles, with two or more joined together where they come out of the branch, you are probably looking at a pine tree.
- If you hold a single needle between two fingers and you can roll it easily because it has multiple sides, it’s probably a spruce tree.
- If the needle you hold between your fingers doesn’t roll easily because it’s flat and two-sided, it’s probably a fir tree.
Scales are little curved shield-shaped pieces that overlap up the twig instead of the more common needles. Three common conifers with scales are:
Junipers which, as mentioned earlier, have unusually fleshy, small blue-black, berry-shaped cones.
Cedars, which in the U.S. are not real cedars, but are a form of juniper that has scales that grow on flattened sprays or all around the twig.
Cypress which may start out with needles, but which change to scales on mature trees.
Now that you have this basic identification knowledge of conifers, your next step in developing expertise will include knowing:
In the meantime, this handy illustration will help you identify the more common conifers.
Once we get into broadleaf trees, or hardwoods, the number of variations multiplies.
Eventually, you might want to learn about all the identifiers of a tree: its leaves, bark, twigs, fruit/flower and overall shape.
However, for now, let’s start building your identification muscles by looking at the easiest way to identify a particular broadleaf tree: by its leaves.
Some broadleaf trees have such famous shapes that they can be identified by their leaf alone. The distinctive Canadian maple leaf is one.
But even leaves that are less famous can help you identify a tree if you know what to look for.
Here is a simplified checklist
simple or compound?
Compound leaf structure
if compound, pinnate or palmate?
Arrangement on the stem
opposite, alternate or whorled?
linear, cordate, lanceolate, reniform, spatulate or something else?
entire, serrate, lobate or other?
pinnate venation or palmate venation?
Let’s look at them one by one.
Broadleaf trees can have simple or compound leaves.
- A simple leaf is arranged as just one single leaf attached to a stem.
- A compound leaf has multiple leaves attached to a stem in a specific pattern.
- A doubly compound leaf has multiple leaves attached to multiple leaves!
Compound leaf structure
Compared with a simple leaf, the little leaves that make up a compound leaf are called leaflets and can be arranged in one of two ways: pinnately or palmately.
- If the leaflets are arranged in rows up along a single center vein, it is a pinnately compound leaf. Walnut, pecan and ash trees are examples.
- If all the leaflets originate from the same point, it is a palmately compound leaf. Horse chestnut and buckeye trees are examples.
Arrangement on the stem
Leaves can be attached to the stem in various ways: opposite, alternate and whorled, for example. Leaves that are attached:
In pairs, across from one another, are called opposite (1).
Progressively on alternating sides, moving up the stem or twig, are called alternate (2).
In groupings of three or more, all at the same level and usually in some symmetrical pattern, are called whorled (3).
To find the shape of a leaf, look at its outline. What does it look like? Is it long and thin (‘linear’), heart-shaped (‘cordate’), lance-shaped (‘lanceolate’), kidney-shaped (‘reniform’), spoon-shaped (or ‘spatulate’) or something else?
Leaves can have many different edges, or ‘margins.’ Some more common edges include:
- A smooth (or ‘entire’) edge like a magnolia;
- An edge with regular or irregular indentations and protrusions that create ‘lobes’ (or ‘lobate’) like an oak.
- A saw-tooth (or ‘serrate’) edge like an elm; and
If you look at the veins in a leaf, most will follow one of two patterns:
- With pinnate venation, the veins all come off the central midrib and go out to the leaf edge. Oak and cherry are examples.
- With palmate venation, all the veins radiate fan-like from a single point at the leaf’s base. Maple and sweetgum are examples.
Common types of broadleaf trees include:
The Importance of Location
Not all broadleaf trees grow in all parts of the U.S., so identifying where the tree is planted will dramatically reduce our options and streamline our search. We can establish our location in two ways:
By geography The state or region of the country, such as Northeast, Pacific Northwest, Southwest and others.
Using What You Know
As you build the inventory of trees you recognize in your region, one way to add more is to use the checklist provided above. Let’s gather as much as we can from the following tree in Oregon’s coastal forest.
- Leaf structure: simple,3-6 inch leaf
- Compound leaf structure: not applicable
- Arrangement on the stem: alternate
- Leaf shape: egg-shaped, or oval, with a pointed tip
- Leaf margins: serrated, with edges that curl under
- Leaf veins: pinnate venation, very distinct midrib with straight veins