Dichotomous Key

A dichotomous key is a powerful tool for use in biology or any of the life sciences. It is also used in logic problems, physical sciences, and many other avenues. They are identified by having a choice of one of two options. Each selection will lead you to another pair of choices that ultimately leads to a final conclusion or organism identification.

They can be used in various fashions, from sorting playing cards
playing card key

to identifying trees (while this is not a true dichotomous key – there are more than two choices for some of the steps – it helps show the branching process).

For more practice, try the following site:


If you have a tree that you are trying to identify, dichotomous keys are a good way to figure out what species you are dealing with. If you have a tree that you are trying to identify, try using the following dichotomous key from the OSU website: