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.
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: