A biological key, also known as an identification key or a dichotomous key, is a way to classify organisms by giving the classifier two options in each stage until identification occurs. For example, in order to identify the tree, a biological key gives two choices – conifer or broadleaf – with a description of each one. Depending on the answer, another question pops up to narrow down the species.
The biological key works by reducing the number of possible identities for a species until the right one is reached by using questions with only two answers, according to Dictionary.com. In order for them to be successful, biological keys must have sound designs. A key needs to be diagnostic, which means that it needs to focus on the characteristics unique to a particular group. A key also needs to be differential, separating a group based on differences. A key needs to be redundant; certain characteristics should be revisited to improve reliability.
Terminology is an important aspect of a biological key. The wording needs to be uniform and consistent throughout the key, and the two possible answers need to parallel each other as much as possible. If a color and blossom size for a flower in one option is given, then the other option also needs to include a color and blossom size.