Creating a Dichotomous Key

In constructing keys, keep the following in mind:

              1. Remember to have a title that describes what the key is about
              2. Start with the most general characteristics and progress to increasingly more specific characteristics.
              3. Use constant measurements, not ones that are highly variable.
              4. Use measurements when possible, avoiding descriptors like large or small if possible.
              5. Use characteristics that are found year-round, not seasonal if at all possible (sometimes the point of a key is identifying organisms based on seasonal
                characteristics, such as flowers). If your key is seasonal, indicate it in the title of the key.
              6. Remember each time a couplet is completed, all organisms must fit into one of the remaining categories or have been named.
              7. Always provide two choices or a couplet.
              8. After each choice in a couplet, tell the user where to go or the name of the specimen.
              9. When constructing a key, all of the items must fall into the pathway that you are creating. For example:

Your key would be wrong, because Mrs. Donley is not a boy so the pathway is invalid.


If we said we were making a key with shapes, and said that a rectangle is a shape, and a square is a rectangle, then
an armadillo would not fit into the key at all.