A dichotomous key is a method of identification whereby groups of organisms are divided into two categories repeatedly

• With each sequential division, more information is revealed about the specific features of a particular organism
  

• When the organism no longer shares its totality of selected characteristics with any other organism, it has been identified
  

When using a dichotomous key to identify specimens it is preferable to use immutable features (i.e. features that do not change)

• Size, colouration and behavioural patterns may all vary amongst individuals and across lifetimes
  

• Physical structures (e.g number of limbs) and biological processes (e.g. reproduction methods) make for better characteristics
  

Dichotomous keys are usually represented in one of two ways:

• As a branching flowchart (diagrammatic representation)
  

• As a series of paired statements laid out in a numbered sequence (descriptive representation)
  

Dichotomous Key