Identification of Plants

All known plant species have names. Unfortunately, outside of flower shops and botanical gardens, they do not come with nametags. Therefore, it is often necessary to identify an unknown plant, that is, to determine the species to which it belongs and thus its name. Identification assumes that the plants have already been classified and named. When you identify a plant, you are basically asking: "Of all known species, which one most closely resembles this individual in my hand?"

Professionals and serious amateurs identify plants by keying. This is a stepwise process of elimination that uses a series of paired contrasting statements, known as a dichotomous key. Keying is like a trip down a repeatedly forking road: If at the first fork you turn right, you cannot possibly reach any of the towns that lie along the left fork. Each successive fork in the road eliminates other towns, until you finally reach your destination.

When keying, the user begins by reading the first pair of statements (called a couplet). For example, a key may begin by asking the user to decide between "plants woody" and "plants not woody." If the unknown is woody, all nonwoody species are immediately eliminated from consideration. Successive couplets will eliminate further possibilities until only one remains, which is the species to which the unknown must belong. The advantage of this procedure is that the user must only make one decision at a time, rather than mentally juggling long lists of features of many possible candidates.

Once the plant has been keyed, it is necessary to confirm the identification. Most books that include keys also include detailed descriptions; some also include illustrations of all or selected species. If the specimen that was keyed matches the appropriate description and/or illustration, the identification may be assumed to be correct. If one has access to an herbarium, the specimen that was keyed can be compared to previously identified specimens of the species as a further check of the identification.

Although plant classifications are based upon information from many disciplines, including genetics, chemistry, and molecular biology, identification almost always relies on readily observed structural features, both vegetative and reproductive. For this reason, it is essential that specimens for identification be as complete as possible. Those of small plants should include not only all aboveground portions but also the roots. For large woody plants, a fully expanded twig of the current season will suffice. In all cases, specimens must include reproductive structures (i.e., flowers, fruits, seeds). Features that are not represented in the physical specimen (e.g., height or girth of trees, features of the bark, colors or odors that fade in drying) should be noted at the time of collection.

Equipment requirements to identify plants are few: a magnifying lens of 10 to 300 power, a 10-centimeter ruler, simple dissecting tools (forceps, teasing needles, razor blades), and a key. An excellent bibliography of appropriate keys for plants of all parts of Earth is provided by Frodin (1983). As for personal requirements, the most important is a critical eye, that is, the ability to observe carefully and to correctly interpret what is observed. This requires some familiarity with both plant structures and the terminology used to describe them. A comprehensive resource for this topic is Radford's introductory textbook (1986). Above all, as with most skills, there is no substitute for plenty of practice.

see also Flora; Flowers; Herbaria; Inflorescence; Systematics, Molecular; Systematics, Plant; Taxonomic Keys; Taxonomy.

Thomas G. Lammers

Bibliography

Frodin, D. G. Guide to Standard Floras of the World. Cambridge, England: Cambridge University Press, 1983.

Jones, Samuel B., Jr., and Arlene E. Luchsinger. Plant Systematics. New York: McGraw-Hill, 1979.

Judd, Walter S., C. S. Campbell, Elizabeth A. Kellogg, and Peter F. Stevens. Plant Systematics: A Phylogenetic Approach. Sunderland, MA: Sinauer, 1999.

Radford, Albert E. Fundamentals of Plant Systematics. New York: Harper & Row, 1986.