We will also survey the five-kingdom model of classification, using examples from the plant and animal kingdoms. We will study the process of placing the groups in their ranks, or taxa, from kingdom to species. In doing so, we will see how much information can be gained through the process of classification. This process will also enable us to perceive the great diversity of God's creation.
The Dichotomous Key
One of the most basic tools of the taxonomist is the key. A key is a sorting device that lists choices between certain observed characteristics. These choices are listed in a sequence that leads to the identification of an unknown specimen. A key may be designed to tell only the group to which an organism belongs, or to tell us its scientific name. To be effective, the choices must be parallel; that is, each must offer a choice between colors or between leaf shapes. A key to distinguishing between sunflowers and daisies, for example, might include flower color. The simplest choice is between two statements.
Flower heads with brown centers--sunflower
Flower head with yellow centers--daisy
Another criterion for an effective key is that each choice includes the smallest number of choices possible. A dichotomous key is such a key. It is the simplest means of identification. The word dichotomy means cut or split into two parts. Hence, a dichotomous key is a two-part or two-choice key. It asks whether a particular organism has either one trait or the other--either yellow or brown, either large or small.
Keys are helpful in increasing your observation and awareness skills. The more you key the better your skills will become. A key may be used to classify rocks and minerals, buttons, words, seeds, and so on. If you have a hobby, you have probably been practicing taxonomic principles whenever you sort or group.
Click here for an example of a dichotomous key.
Dichotomous keys may come in more than one form. This key still uses two choices, but instead of A or AA choices (as seen in the first accompanying project), the form is more like a follow-the-number scheme until the specimen is identified.
The following animal key is an actual key used in the classification of toads and frogs of the mid-United States.
| Key to Some Common Toad and Frog Species | Answer or next key step |
| 1. | Skin very warty; swollen glands on sides of neck; |
|
| bony ridges between eyes | 2 |
| Skin not very warty; no swollen glands; no bony ridges | 4 |
| 2. | Warts in two series, large and small mixed; length |
|
| of swollen neck glands longer than distance between | 3 |
| Warts of nearly same size; dark blotches contain |
|
| many small warts; length of swollen neck glands |
|
| shorter than distance between | Great Plains Toad, |
|
| Bufo cognatus |
| 3. | Dark blotches contain three or more warts; warts on |
|
| legs not much larger than those on feet | Fowler's Toad, |
|
| Bulo woodhousei |
| Dark blotches contain one or two warts; some |
|
| of warts on legs much larger than those on feet | American Toad, |
|
| Bufo terrestris |
| 4. | Finger and toe tips with expanded, adhesive discs | Family Hylidae 5 |
| Finger and toe tips without discs | Family Ranidae 8 |
| 5. | Finger discs small, not wider than its finger | 6 |
| Finger discs wider than fingers | 7 |
| 6. | Skin rough; toe webbing obvious; no pattern on back; dark, |
|
| triangular mark between eyes | Cricket Frog, |
|
| Acris gryllus |
| Skin smooth; toes less than half webbed; back pattern three |
|
| long lines | Chorus Frog |
|
| Pseudacris nigrita |
| 7. | Color pale brown; a pale X on back; discs on fingers and toes |
|
| not very obvious | Spring peeper |
|
| Hyla crucifer |
| Color green, brownish, or grayish; back pattern blotches, but |
|
| not X; finger and toe discs large and obvious | Gray Tree Frog |
|
| Hyla versicolor |
| 8. | Lateral ridges extending from head to back not obvious | 9 |
| Lateral ridges obvious | 10 |
| 9. | Sizes 5 to 8 cm in adult; brown blotches on back, white below; |
|
| when living produce distinct odor | Mink Frog, |
|
| Rana septentrionalis |
| Size very large: some or no spotting on back; grayish below | Bull Frog, |
|
| Rana catesbiana |
| 10. | Other folds between lateral ridges on back; black spot on back |
|
| of elbow | 11 |
| Skin smooth between lateral ridges; no spot on elbow | 14 |
| 11. | Back with no large black spots | Plain Leopard Frog, |
|
| Rana pipiens (variety) |
| Back with large spots | 12 |
| 12. | Spots obvious on plain color | 13 |
| Spots not obvious, spots mixed with dark blotches | Kandyohi Leopard Frog, |
|
| Rana pipiens (variety) |
| 13. | Spots square; when living, bright yellow underneath legs | Pickerel Frog, |
|
| Rana palustris |
| Spots rounded; when living, whitish underneath legs | Leopard Frog, |
|
| Rana pipiens |
| 14. | Brown color; black ear patch; knob on outer sole | Wood Frog, |
|
| Rana sylvatica |
| Living, green color; no black ear patch; knob absent | Green Frog, |
|
| Rana clamitans |
