A student of taxonomy was puzzled when told by his professor to look for  a key to identify a plant. He went to his friend to clarify what ‘key’ the professor was referring to? What would the friend explain to him?

Identification of a plant is a scientific process. One has to study the general morphological characters along with its habitat, place of collection, time of flowering, etc., for identification. Several reference materials are available in the form of taxonomic keys. Professor meant to refer to these keys to help the student to identify the plant.
This concept of key was introduced by Ray. Separate taxonomic keys are required for each
taxonomic category. Keys are analytical in nature and are used as reference to help in
identification of a newly discovered plant.