Taxonomic keys are a written means of helping people to identify an unknown plant. Looking randomly through a flora that includes thousands of plants would take far too much time. A key provides a structure for sorting through a great deal of information, so that the user can quickly and automatically skip over many species that do not resemble the plant.

A key is written as a series of couplets. Each couplet consists of two opposing descriptions of some features of a plant. The user chooses the description that best fits the unknown plant, and is guided by that choice to another couplet or to an answer. The two halves of the couplet lead the user to different parts of the key, dealing with different subgroups of the plants included in the key. All of the plants in the half that was not chosen are instantly...