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TAXONOMY OVERVIEW

This page is meant to introduce dendrology, classification systems, and nomenclature used to name species of trees, as preparation all the information within the rest of this web site, in the textbook, and on your CD maybe.  Chapters 2-3 in the textbook are also pretty good.

Dendrology

This course could also be called “Dendrology,” which we define as the study of tree classification, nomenclature, habitat, and range.  In other words, in this course you will learn how trees are divided into similar groups, how and why trees are so named, the names of many of the trees that dominate forests in North America, and where on the landscape these trees grow.  You will also learn about the ecological importance of these trees in ecosystems, and ways that people use them (culturally and economically). 

Classification

Classification is something that we do every day, probably every waking hour.  In short, classification is the ordering of items into groups having common characteristics.  For example, most of us would classify a metal/plastic object weighing thousands of pounds, having 4 rubber wheels, and moving along a road, as... an automobile.  In this way, we place this object into a group (automobiles) that share common characteristics that are meaningful or important to us.  In the same way, people classify trees, and even forests, just to aid in communication. 

 Why is classification of trees and forests necessary?

      1.      The physical environment, biotic resources, and food webs to support productive forests during at least some seral stages.

2.      Resistance to catastrophic change and/or the capacity to recover from such change at the landscape level.

3.      A functional equilibrium between supply and demand of essential resources (water, nutrients, light, growing space) for major portions of the vegetation.

4.      A diversity of seral stages and stand structures that provide habitat for many native species and all essential ecosystem processes.

Note: More information on this definition can be found in:  Kolb, T.E., Wagner, M.R., and Covington, W.W.  1994.   Concepts of forest health.  Journal of Forestry 92(7):10-15.  Even more information on forest health is available at: http://www.for.nau.edu/forhlth/

 Nomenclature

 "Nomenclature" is a system of names.  People generally name plants (and animals) using 2 different systems, both of which will be used in this course:

1.  Common names: Many people refer to trees using a common name; for example, ponderosa pine, or quaking aspen.  Such use is acceptable when there is no confusion about the subject tree.  However, there are no formal rules that govern the use of common names.  A result is that different common names may be used to refer to the same tree.  Ponderosa pine, for example, has also been called “western yellow pine,” “blackjack pine,” “bull pine,” and “Arizona white pine.”  Also, it is possible for 2 different tree species to have the same common name.  For example, many species of pine are called “yellow pine” or “hard pine” in some areas of the US.  These examples show that common names can be confusing because each tree species does not always have a unique name. 

 2.  Scientific names: In the late 1700s, the Swedish botanist Linnaeus developed a system of classification that assigns a unique name to each and every species.  Both plants and animals can be named using this system.  The system consists of a hierarchy of categories, with members of each category having similar characteristics.  Also, members in a level in the hierarchy share common characteristics with all members in higher levels.  Originally, Linnaeus based these categories on flower characteristics, such as the number of stamens and pistils, but more recently, other characteristics that reflect evolutionary relationships among plants are also used (e.g., similarity in plant parts other than flowers, genes, habitat, geographical range).  Let’s look at an example of this system of classification using ponderosa pine:

            Kingdom                     Plant                

            Class                          Pinophyta

            Order                         Pinales

            Family                        Pinaceae

            Genus                         Pinus

            Species                       ponderosa

We usually do not use all these names to refer to the scientific name of ponderosa pine.  Instead, in Forestry we use a system of “binomial nomenclature,” meaning a system of "2 words", to make this unique name.  The first word in the system is the genus name, and the second is the species name.  For example, the binomial scientific name of ponderosa pine is: Pinus ponderosa.  No other plant is called by this name; it is unique!  "Pinus" is the genus name, and "ponderosa" is the species name. 

Note:  both names are italicized (or underlined on old typewriters) because they are written in a "foreign" language: Latin.  Why Latin?  Because Latin is a so-called “dead language,” meaning that it is an ancient language that is rarely used today;  thus, its terms and structure are not changing the way that current languages can change.  Also note that the genus name is always capitalized, and the species name is not...ever.

The Latin words used for genus and species names often have meanings that contain information about the tree.  Guess what Pinus means in Latin?  If you guessed “pine tree,” you are correct.  And ponderosa?  This word means “large” or “heavy” in Latin.  So, the scientific name Pinus ponderosa, means a large pine tree in Latin. Let’s look at some other meanings of tree Latin names:

Note that Latin names can contain several types of information about the plant.  Often, the name is based on a Latin word for a certain type of tree (e.g., Quercus for oak).  Or, the name may imply something about the appearance of the tree.  For example, Acer means sharp in Latin, and many maples have sharp points or lobes on their leaves; rubra means red.  The Latin name may tell us something about the places where the plant grows (e.g., neomexicana, growing in New Mexico).  Finally, the species Latin name may commemorate a person that first discovered the plant or named it (e.g., engelmannii, after the botanist George Engelmann). 

In the table, also note that some common names start with a capital (New Mexican locust), and others do not (bigtooth maple).  In general, common names are not capitalized.  However, when the common name is based on a proper noun (i.e., the name of a well-recognized person or place) it starts with a capital.  For example, "New Mexican" is capitalized in “New Mexican locust” because it is named after a U.S. state.  Another example is “Engelmann spruce,” which is named for Mr. Engelmann.  If you want more information on the meaning of plant Latin names, we recommend the following books:

Gledhill, D. 1989.  The Names of Plants (2nd Edition).  Cambridge University Press, Cambridge, UK.

Or just read in your textbook:  Hardin, J.W., Leopold, D.J., and White, F.M.  2001. Textbook of Dendrology (9th Edition).  McGraw Hill, NY.... Chapter 3.

Intraspecific Taxa

Above we discussed nomenclature that is used to refer to different plant species.  For some plants, there are well-recognized categories, or taxa, within a species.  In other words, there are “intraspecific taxa.”  “Taxa” is the plural of “taxon,” which is a group of organisms sharing similar characteristics.  You should be aware of 3 different intraspecific taxa for this course:

 1.  Variety: A subset of plants within a species that is so genetically distinct as to warrant formal recognition, but not distinct enough to be considered a species. Let’s look at an example using ponderosa pine, which has two main varieties:  Pinus ponderosa var. ponderosa and Pinus ponderosa var. scopulorum

    Variety ponderosa grows on the west side of the Cascade and Sierra Nevada Mountains, whereas variety scopulorum grows in the Rocky Mountains, Southwest, and Mexico.  They differ genetically in cold hardiness, drought tolerance, and other characteristics.   Variety ponderosa is less cold hardy and drought tolerant than variety scopulorum, and these characteristics are genetically based.  In other words, if you grew both varieties together on the same site, they would differ in these characteristics.  Clearly, these two varieties are genetically different, but they are similar enough that both are still considered to be members of the species Pinus ponderosa.  A variety may eventually evolve to become a distinct species if differences between it and other varieties of the same species increase over time.

2.  Cultivar: A variety often used used in horticulture, landscaping, or urban forestry.  Cultivars typically rather uniform genetically and morphologically because many are propagated asexually, by cuttings, grafting, or other ways of cloning.  Many cultivars are maintained by human cultivation; they would not occur widely without man’s influence. 

    An example of a cultivar is the thornless, ‘sunburst’ variety of honeylocust, Gleditsia triacanthos var. inermis cultivar sunburst.  Honeylocust growing in the wild have hundreds of long, sharp thorns that protrude from the bark.  These thorns limit animal feeding on the large, nutritious fruits of this tree.  However, certain individuals of this tree do not produce thorns, and have unusually yellow leaves because of a genetic mutation.  These individuals were propagated by humans because they make excellent shade trees, and named Gleditsia triacanthos var. inermis cultivar sunburst.  The variety name “inermis” means “unarmed,” and the cultivar name “sunburst” describes the yellow leaves (note that the variety name is italicized, but the cultivar name is not).  This cultivar is one of the most common street trees in many US cities.  It is not common growing in the wild because its unique characteristics probably reduce its competitive ability against other plants.  For example, the yellow leaves probably reduce photosynthesis, and the lack of thorns likely increases animal feeding on its fruit.  However, when grown in exotic environments, like cities, where competition and reproduction are not as important, the cultivar grows well, and is favored by humans.