The groupings just listed are especially helpful for narrowing the choices when plants are being selected to serve a function, play a role, or solve a problem. There still remains the need to identify plants specifically; for example, to recognize the difference between red oaks and live oaks or between zinnias and dahlias, or to recognize deciduous plants by their winter twigs after leaves, flowers, fruit, or other helpful features are gone.
There are several kinds of identification. The simplest, and at the same time the most complex, is identification through recognition, often built on a lifetime of association and familiarity. If someone asked how you identify your best friends, it might be difficult to describe the mental process behind the recognition. The combination of body build, facial features, hair and eye color, manner of walking, voice pattern, and
more, all identify a certain individual. Having a mental picture of that friend then allows us to take only one feature, such as the voice on the telephone, and reconstruct the total person in our mind’s eye. Similar identification becomes possible with plants after repeated exposure to the same species. How the plants were first learned is forgotten and the ability to recognize those plants in nearly all situations becomes a part of our permanent learning.
Another, less precise, kind of identification occurs when a plant species is recognized as belonging to a group but the exact species name is not known. For example, you may know it’s a spruce, but not know which spruce. Such a level of identification serves many professional horticulturists who have no particular need for precision. The exact basis for the ability to recognize at least the genus of the plant may be as lost in memory as that described earlier.
Finally, there is the kind in which the horticulturist has absolutely no idea what the plant is and must begin a methodical process of identification through searching and gradual elimination. Knowing that in all probability the plant has been identified, classified, named, and entered into the scientific literature offers some comfort when faced with the identification of an unknown. Even then it seems like a monumental task trying to identify one plant from among the thousands and thousands of species on the earth.
Sometimes there are shortcuts. For instance, if the plant is known to be a broad-leaved evergreen, or a flowering woody shrub, or a cactus, you can go to specialized texts in which a description or photo may be found. Perhaps someone from the state university or the local county agent can identify the plant. Such questions can be directed to them with clear conscience, but it is still no substitute for knowing how to find out yourself.
The tracing of unknown plants, especially the economically important ornamentals, requires the use of a dichotomous analytical key. There are hundreds of such keys, some dealing with a limited group of plants, others more encompassing. All present the searcher with a series of couplets and pursue identification through a process of elimination. Each couplet consists of two contrasting statements. The searcher chooses the statement that best describes the unknown plant. Beneath that statement will be another couplet, again requiring the selection of one and elimination of the other. The process continues until all species have been rejected except the one to which the plant belongs.
These keys are based in large part on physical features of the plant rather than physiological or evolutionary relationships. Very complex and inclusive keys such as the one published in 1949 by Liberty Hyde Bailey, Manual of Cultivated Plants Most Commonly Grown in the Continental United States and Canada (Revised edition, Macmillan, New York) often require information unknown to the searcher. For example, the couplets may require the choice between flowers with five petals or multiples of five and flowers with six petals or multiples of six. If the unknown plant has no flowers attached, the tracing can get off track very easily.
For the beginner, it is best to begin with a simpler key. Consider the following simplistic example to understand how keys work. Only genera (the plural of genus) are being identified.
1. Plant evergreen
2. Leaves needle-like
3. Needles separate
4. Needles stiff and sharp, four sided. . . . Spruce (Picea)
4. Needles flat with two white lines on
underside. . . . Hemlock (Tsuga)
3. Needles grouped in fascicles. . . . Pine (Pinus)
2. Leaves broad and flat
5. Leaves oval in shape, not spiny
6. Flowers large, compound, and showy. . . . (rhododendron)
6. Flowers small, fascicled, and belllike. . . . andromeda (Pieris)
5. Leaves holly-like and spiny. . . . Oregon-grape (Mahonia)
1. Plant deciduous
Keys are seldom this simple but at least the concept of dichotomous couplets can be appreciated.