Lesson 7: Tree Identification

 

Almost 800 species of native and naturalized trees grow in North America. As many as 160 of these grow in Maryland. The ability to recognize the major tree species and their distinguishing characteristics is basic to forestry. Dendrology, the study of trees, encompasses the classification, nomenclature, and identification of woody plants. Find a special glossary for this lesson on this page (opens in a new tab): Special Glossary of Plant Taxonomy

 

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Classification

In the 18th century, Carolus Linnaeus developed a system for classifying plants based on their flowering and reproduction. Taxonomists have since divided almost all trees into two groups, the gymnosperms, or conifers, and the angiosperms, or broadleaf trees. These divisions are further broken down into order, family, genus, and species.

All individuals with similar characteristics are considered a species. A collection of closely related species is called a genus. A family is composed of all the genera (plural of "genus") that share common characteristics. Sometimes, a cultivar or variety of a species is found. These individuals exhibit minor differences in such things as needle length, for example, from others of their species. Occasionally, two species will cross-pollinate and form a hybrid. 

Table 7-1: Classification of the Beech Family

Family	Fagaceae (Beech)
Genus	Fagus (Beeches)
Species	grandifolia (American beech)
Genus	Castanea (Chestnuts and Chinkapins)
Species	dentata (American chestnut)
Species	pumila (Allegheny chinkapin)
Genus	Quercus (Oaks)
Species	alba (White oak)
Species	falcata (Southern red oak)
Variety	falcata variety Pagodaefolia (Swamp red oak)
Species	rubra (Northern red oak)
Species	palustris (Pin oak)
Species	phellos (Willow oak)

 

Other, common terms outside the language of taxonomic classification describe groups of trees, terms such as “deciduous,” “evergreen,” “hardwood,” and “conifer.”

Deciduous refers to trees that shed their leaves during the fall. Trees that retain their foliage year-round are evergreen. In North America, most broadleaf trees are deciduous, and most conifers evergreen. However, there are exceptions; for example, the American holly is an evergreen broadleaf and the bald cypress a deciduous conifer.

Usually, the wood of broadleaf trees is more dense, and therefore harder, than the wood of conifers. As a result, broadleafs are often known as hardwoods. Conifers are likewise referred to as softwoods. However, the wood of some broadleaf trees is quite soft—the aspen is an example—and the wood of some conifers is relatively hard—such as the southern pine.

 

 

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Nomenclature

All trees have one or more names by which they are commonly known. A name can be based on distinct features (shagbark hickory), locality (Virginia pine), use (sugar maple), habitat (swamp maple), a commemoration (Engelmann spruce); a name can also be an adaptation of a name from another language (sassafras). Common names can vary from place to place, resulting in some confusion. Therefore, it is helpful to know the scientific, or Latin, name as well.

The scientific name consists of two parts: a generic name (genus), referring to the group the tree belongs to, and a specific name, identifying the individual species. The scientific name is universally recognized and unique to a particular tree. (See Appendix 3 Download Appendix 3 for common and scientific names.)

 

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Identification

With practice you will learn to recognize most of the major forest trees. It is necessary to know taxonomic keys for identifying unfamiliar species. Before attempting to use a taxonomic key, first become familiar with distinguishing features of trees—leaves, fruit, bark, twigs, flowers, shape, and habitat.

 

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Leaves

Leaf arrangement, shape, size, color, venation, texture, and margin all provide clues to a tree's identity.

 

• Leaf arrangement.

Leaves are produced in set intervals along the twig. In most tree species, a single leaf occurs at the point of attachment or node, and leaves appear to alternate with each other on the twig, in an alternate arrangement. Less frequently, a pair of leaves emerges from the node, in an opposite arrangement. If more than two leaves appear at a common node, they are whorled.

Each leaf consists of a blade extending from a leafstalk, which is attached to a woody stem. If the blade is all in one piece, it is known as a simple leaf. A compound leaf has two or more separate blades, or leaflets, attached to the central leafstalk. A leaflet may look like a leaf, but leaflets are distinct: they have no bud at the base and leave no definite leaf scar when picked. Hickories, walnut, and the ashes are examples of trees with compound leaves.

The leaves, or needles, of pines grow in fascicles, or bundles. The number of needles making up the fascicle varies from species to species. For example, loblolly pine needles grow in fascicles of 2 or 3, while white pine needles grow in fascicles of 5.

For illustrations of leaf arrangements, see page 3, first two rows in Appendix 2, "Leaf Keys to Common Trees in Maryland."

• Leaf shape and size.

The size and shape of a leaf are characteristic for a species and of tremendous value in tree identification. The common leaf shapes are illustrated in Appendix 2, "Leaf Keys to Common Trees in Maryland," pages 7-25. Occasionally, leaf variations appear in the same tree; for example, the sassafras has three distinctly different leaf shapes.

• Leaf margins.

The margin, the edge of the leaf blade, can be smooth, toothed, or lobed. Appendix 2 illustrates common leaf margins (page 3, third row).

• Leaf surface.

Leaves exhibit various textures-thin or thick, and smooth, waxy, or pubescent (hairy). Some leaves are smooth on top and hairy underneath.

• Venation.

In broadleaf trees, leaf veins usually follow one of four patterns: parallel, or closed venation, in which the veins run nearly parallel to each other, from the base to the apex of the leaf, resulting in a "closed" system; palmate venation, in which three or more secondary veins branch from the base of the leaf; pinnate venation, in which the midrib extends the length of the leaf, with secondary veins branching off; or arcuate venation, which is a modification of pinnate venation. Figure 7-1 illustrates leaf venation.

 

 

Figure 7-1: Leaf Venation. From Patrick, Steven R. 4-H Forestry Judging Handbook, University of Georgia Extension, 2001

 

• Leaf color.

Particularly in the fall, color offers a clue to leaf identity. However, even in the spring and summer, leaves vary in intensity of color.

 

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Twigs

A distinguishing characteristic of twigs is the opposite or alternate arrangement of leaves and assorted buds. Other twig characteristics include the size and shape of the bud, leaf and bud scars, presence of lenticels, pith formation, color, and odor. Sometimes, thorns, corky ridges, pubescence, or spines also appear. For example, what identifies the black walnut is its smooth, stout twigs; a light brown chambered pith; fuzzy buds; large leaf scars; and bundle scars in groups of three. Figure 7-2 illustrates some of the common characteristics of twigs.

Figure 7-2. Twig and Bud Characteristics

 

Bark

Each tree species has its own characteristic bark; variation occurs in texture, color, and thickness. Often, bark alone identifies a tree. Bark can be smooth or rough, with furrows that run lengthwise along the trunk. Furrows range from shallow to deep, depending on the species. In other trees, bark is divided into rectangular plates. Sometimes, the bark becomes scaly and, occasionally, sloughs off. Trees such as firs have a soft corky bark; other trees, such as the shagbark hickory, have bark described as “shredded” or fibrous. The color, texture, and thickness of bark can vary considerably as a tree matures.

 

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Fruit

Fruit is the seed-bearing organ of the plant. Because fruits vary widely in size, shape, color, and form, they are helpful in tree identification. Various fruits include nuts, berries, drupes, pomes, legumes, achenes, samaras, and pods. See Figure 7-3 for illustrations of some common fruit.

 

 

Figure 7-3: Fruits of common trees. Image courtesy University of Delaware.

 

Form

As the tree grows, it begins to assume a characteristic size and shape. Appearance is influenced by the form of the trunk; the shape, size, and density of the crown; and the number of branches and direction of their growth. For example, firs and spruces develop a conical, or “Christmas tree” shape. The round dome of the mature white oak distinguishes the tree, from a distance. The American elm is known for its graceful, vaselike crown. Other helpful identifying characteristics are the persistence of dead branches (some trees do not drop their lower dead branches) and buttressing or swelling of the lower trunk (often found in swamp species).

 

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Habitat and Range

Most trees require specific site conditions to grow and survive, including moisture, light, and soil type. Trees will commonly grow in association with other species that favor the same conditions. A quick survey of the site is useful for predicting the type of species the site will support.

 

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For more information

See Appendix 2. Leaf Key to Common Trees in Maryland.

Many other books are available to help in the study and identification of forest trees. Choose one that meets your needs. The following books are excellent references and should be readily available at your local library or book store:

• Elias, T.S. 1980. The Complete Trees of North America: Field Guide and Natural History. Outdoor Life/Nature Books. New York: Van Nostrand Reinhold Co.
• Harlow, W.M. 1946. Fruit Key and Twig Key to Trees and Shrubs. New York: Dover Publications.
• Harrar, E.S., and J.G. Harrar. 1962. Guide to Southern Trees. New York: Dover Publications.
• Petrides, G.A. 1972. A Field Guide to Trees and Shrubs. Peterson Field Guide 11.  Boston: Houghton Mifflin Co.
• Sutton, A., and M. Sutton. 1992. The Audubon Society Nature Guides—Eastern Forests.  New York: Chanticleer Press, Inc.
• Taylor, Norman. 1961. Taylor's Guide to Trees. Boston: Houghton Mifflin Co.
• Zim, H.S., and A.C. Martin. 1956. Trees.  New York: Golden Press.

The two books below are also good references, but may be more difficult to find locally. To purchase a copy, contact the sources listed.

• Brown, Russell G., and Melvin L. Brown. 1972. Woody Plants of Maryland. Baltimore: Port City Press. (Out of print but used copies may be available.)
• Taber, William S. 1995. Delaware Trees. Wilmington, DE: Associates International, Inc. (A great book that describes trees in the Mid-Atlantic region. It is only available through the Delaware Department of Agriculture Forest Service. Phone number: 302-698-4547. Email: gail.ingram.smith@state.de.us.)

For additional assistance, refer to other tree identification publications or the following websites:

• http://www.dendro.cnre.vt.edu/ Links to an external site.
• http://www.oplin.org/tree/index.html Links to an external site.
• http://uptreeid.com Links to an external site.

 

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References

• Elias, T.S. 1980. The Complete Trees of North America. Outdoor Life/Nature Books. New York: Van Nostrand Reinhold Co.
• Harlow, W.M., and E.S. Harrar. 1969. Textbook of Dendrology. New York: McGraw-Hill Inc.
• Harrar, E.S., and J.G. Harrar. 1962.Guide to Southern Trees. New York: Dover Publications.
• Kundt, J.F., and R.L. Baker. 1970. Leaf Key to Common Trees in Maryland. Maryland Cooperative Extension Service.  Bulletin 238. College Park, MD.
• Petrides, G.A. 1972. A Field Guide to Trees and Shrubs. Peterson Field Guide 11.  Boston: Houghton Mifflin Co.
• Phillips, Claude E. 1975. Trees of Delaware and the Eastern Shore: A Guide to Their Identification in Winter. Newark, DE: University of Delaware Press.
• Preston, R.J. 1976. North American Trees.  Ames, Iowa: Iowa State University Press.
• U.S. Dept. of Agriculture Forest Service. 1988. Forest Statistics for Maryland—1976 and 1986.  Resource Bulletin NE-107.  Washington, DC.

 

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Assignments

Read:

"Tree Identification: Making a Study Collection" (below). Complete the activities as detailed in the box: a) make the plant press, b) collect and identify leaf/twig samples with the different characteristics, and c) identify examples of bark and silhouettes. Use What Tree Is That? A Guide to the More Common Trees Found in the Eastern and Central United States, undated and published by the National Arbor Society, Nebraska City, NE, as a reference.

Fazio, James R. The Woodland Steward: A Practical Guide to the Management of Small Private Forests. Pages 13-19.