Department of Horticulture
Images, Identification, and Information
Plant Identification: Examining Leaves
Pat Breen, Oregon State Univ., Dept. of Horticulture
To identify an item is to recognize the item and associate it with its appropriate name. Such as, that tan automobile in front of our house is a Honda Accord. Or, that large woody plant in the park is a tree, more specifically a Doug-fir. Identifying a landscape or garden plant requires recognizing the plant by one or more characteristics, such as size, form, leaf shape, flower color, odor, etc., and linking that recognition with a name, either a common or so-called scientific name. Accurate identification of a cultivated plant can be very helpful in knowing how it grows (e.g., size shape, texture, etc.) as well as how to care and protect it from pests and diseases.
First let’s look at some common characteristics of plants that are useful in identifying them. Now if this was a botany class dealing with plant systematics, the field of study concerned with identification, naming, classification, and evolution of plants, we would spend a good deal of time on the reproductive parts of plants, i.e., mostly the various parts of the flowers, i.e., ovary, stigma, etc. Structural similarity of reproductive parts is an important means by which plants are categorized, grouped, named, and hence identified. However, with many horticultural plants, especially woody plants, we may have to make an identity without regard to flowers, for often flowers are not present or are very small, and other characteristics may be more obvious. Some plants characteristics are so obvious or unique that we can recognize them without a detailed examination of the plant. Similarly, we can probably all immediately recognize a Volkswagen Beetle among a group of cars in a parking lot.
So what are some plant characteristics that can be used to identify plants?
Leaves are often the basis for identifying plants since they are so easily observed. They usually consist of two parts,
- the blade, the wide or more obvious part of a leaf,
- and the “stalk” or petiole by which the blade is attached to
the stem. There is a bud at the point where the petiole attaches
to the stem [see Sitka Alder, Alnus sinuata, leaf and buds].
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First be aware that all the leaves on a given plant do not have
the same size or even appearance [Betula papyrifera, shoot, comparison].
They may vary in size, color, and even shape [Sassafras albidum,
leaves, fall] and [Malus sargentii, leaves, fall]; those that receive much sun may look different from those in heavy shade.
So when trying to determine the identity of a plant by its leaves, make sure you examine many leaves and
attempt to determine what might be considered “typical” leaf characteristics. Although basketball
players may vary in size, shape, and color, a “typical” physical characteristic of a basketball player often
Broad vs. narrow leaves
Leaves can be divided into categories of broad and narrow.
- Broad leaves have a wide blade, often with a visible network of
- Narrow leaves are slender, without a wide blade, these leaves are often referred to as “needle” or “scale-like”.
Conifers, such as pine (Pinus), spruce (Picea) and juniper (Juniperus), have narrow leaves, some have needles
and others have scale-like leaves,
The pattern by which leaves are attached to a stem or twig is also a useful
characteristic in plant identification. There are two large groups, alternate
and opposite patterns, and a third less common pattern, whorled.
- Alternate leaves have only a single leaf attached at one location (a node) on a stem, often the leaves alternate from one side to the other as one moves along the stem, or they may be in a spiral pattern around the stem.
Eastern Redbud, [Cercis canadensis, leaves]
American Elm, [Ulmus americana, leafy shoot]
Alternate leaves are common in the following genera: Alnus (alder), Crataegus (hawthorn),
Cotoneaster, Magnolia, Prunus, Quercus (oak), and Rubus.
- Opposite leaves refer to two leaves being attached at the same location (a node) on a stem, but opposite one another, that is, on either side of the stem
Common Boxwood, [Buxus sempervirens, leafy shoot]
Katsuratree, [Cercidiphyllum japonicum, leaves]
Dawn Redwood, [Metasequoia glyptostroboides, needles, comparison].
Opposite leaves are common in the following genera: Acer (maple), Buxus (boxwood),
Cornus (dogwood), Euonymus, Fraxinus (ash), Lonicera and Viburnum
- Sometimes more than two leaves arise from the same location (node) on a twig, the leaves may radiate from the twig like the spokes on wheel, this is called a whorled arrangement.
- Occasionally a given plant may exhibit more than a single type of leaf arrangement. For example
in Crape Myrtle (Lagerstroemia indica) the lower leaves of a shoot may have an opposite leaf
arrangement, but toward the end of the shoot the leaves may be alternate or even whorled
[Lagerstroemia indica, shoot].
Simple and compound leaves
Leaves may have a single undivided blade or a blade that is divided into parts.
- Simple leaves have only one leaf blade, with or without a stalk or petiole.
- Compound leaves have more than one blade and may have a complex leaf stalk structure.
There are several different types of compound leaves, the common ones are:
- Palmately compound leaves have three or more leaflets attached at the end of the stalk (petiole) (like fingers on our hands).
- Pinnately compound leaves have a number of leaflets attached along a central stalk.
They can also be:
- double pinnately (bipinnately) compound,
- triple pinnately (tripinnately) compound.
It is not always easy to find the bud at the base of a petiole, it may not be visible early in the growing seaon and sometimes a mature bud is “hidden”, such as being enclosed by the petiole base, such as in
Look at the entire shoot to determine what is a leaf, don’t just look at the end of a branch. Since a bud is at the base of each leaf, it is possible to determine the leaf arrangement (i.e., alternate, opposite, etc.) of a deciduous plant in winter by looking at the arrangement of buds on a bare twig, e.g., Red Maple, [Acer rubrum, shoot branches and buds, winter].
- leaves have a bud at the base of the stalk (petiole), e.g., Paperbark Birch, [Betula papyrifera, shoot, leaves], whereas
- leaflets do not, e.g., American Yellowwood, [Cladrastis kentukea, leaf and Cladrastis kentukea, leafets].
Leaves may be lobed or not lobed. A lobe may be defined as a curved or rounded projection. With leaves there is no clear distinction between shallow lobes and deep teeth. A main vein is often visible in a lobe, this may not occur in teeth.
Another important leaf characteristic for plant identification is the edge or margin of a leaf or leaflet. Leaves have either smooth edges, called entire, or small notches or “teeth” along the margin.
Other leaf characteristics to consider, especially if using a botanical key.
- Entire (smooth):
- Toothed: Teeth may occur at the base of a leaf, at the tip, or along the whole margin. The teeth may vary in number and size.
- Coarsely toothed, may be difficult to distinguish from lobed, e.g., Paperbark Maple, [Acer griseum, leaves and fruit]
- Doubly toothed, Sitka Alder, [Alnus sinuata, leaf margin, surface]
- Serrate: saw toothed, teeth pointing forward
- Single serrate;
Japanese Zelkova, [Zelkova serrata, leafy shoot]
Strawberry Tree, [Arbutus unedo, leaves]
- Doubly serrate, American Elm, [Ulmus americana, leaf margin and tip]
- Spiny-serrate, Wintergreen Barberry, [Berberis julianae, leaves]
- Dentate: having marginal teeth whose apices are perpendicular to the margin and do not point forward, Crimson Glory Vine, [Vitis coignetiae, leaf]
Non-leaf characteristics are also useful in attempting to identify woody plants, these include:
- over all shape (e.g., elliptic, lanceolate,
- shape of base (cuneate [wedge shaped],
cordate, rounded, etc.)
- shape of apex (abrupt, acuminate, acute,
emarginate, mucronate, etc.)
- pattern of veination (e.g., parallel, net-veined, etc.)
- surface properties (e.g., pubescent, glabrous [smooth])
- odor when crushed (strong, foul, absent, etc.)
- flower type, color, and showiness
- fruit type, shape, and color when ripe.
Some characteristics of narrow leaf plants.
Two groups, scale-like and needle leaves.
Scale-like leaves are usually small, short and overlap; they are common in several genera of conifers including junipers (Juniperus), falscypress (Chamaecyparis) and arborvitae (Thuja), for example, Arborvitae and Western Red Cedar (T. plicata) , [Thuja orientalis, branchlets, comparison]. Often scale-like leaves are displayed as two, three or four per node. A hand lens or low power microscope is often necessary to make this determination.
Differences in scale-leaves can be used in distinguishing the following "cedars" native to Oregon (none of which are true Cedars, i.e., Cedrus).
Needle leaves, also common in conifers, they are attached to twigs in several ways:
- Incense Cedar [Calocedrus decurrens, leaves]. Note that 4 leaves appear at the same note, 2 facial (face) and 2 lateral (side), the outline of the pair of lateral leaves trace a "flueted wine glass".
- Port Orford Cedar [Chamaecyparis lawsoniana, leaves]. Leaves are closely pressed in opposite pairs. The lateral leaves are larger than the facial leaves, where the leaves meet on the underside of a branchlet a white waxy line is evident, it appears as an "X" marking. Also note a single dot, a resin gland, is evident on each facial leaf (this may require a hand lens).
- Western Red Cedar [Thuja plicata, leaves]. Note 4 leaves of similar size (2 facial and 2 lateral) appear at a node, the waxy surface markings on the underside of a branchlet are thought to resemble a "butterfly" or a "bow-tie".
- Yellow or Alaska Cedar [Chamaecyparis nootkatensis, leaves]. The 4 small leaves (2 facial and 2 lateral) at a given node are of similar size, no waxy marking is evident were the leaves meet.
See a side-by-side comparison of three of the "cedars" native to Oregon.
- The scale leaves of the native Western Juniper [Juniperus occidentalis, branchlets, leaves] differ markedly from the above "cedar" trees.
- Single -
- attached directly to the twig, for example,
- attached via a peg-like stalk, for example,
- Bundles - grouped in bundles that are attached to the twig; often there are 2, 3, or 5 leaves per bundle. A given tree usually has the same number of needles per bundle. Bundles are common in pine:
- Clusters - usually more than 5, can be 30 or more, for example,
Fir flat needles (usually) and friendly (to the touch, usually, but Spanish Fir is sharp pointed)
Spruce sharp , square (needles in cross-section)
Pine in packages (needles in groups of 2, 3, 5, rarely one)
To identify an unknown plant using the characteristics descried above, in additional to others, one could us a traditional
or a computer data base of plants, such the
Oregon State University Woody Plant Data Base.
Cope, E.A. Muenscher’s Key to Woody Plants: An Expanded Guide to Native and Cultivated Species. 2001. Cornell University Press, Ithaca, New York.
Partyka, R.E., J.W. Rimelspach, B.G. Joyner, and S.A. Carver. 1980. Woody Ornamentals: Plants and Problems. ChemLawn Corp. Columbus, Ohio.
Plant ID Answers