Dichotomous Keys


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•  Construction of dichotomous keys for use in identifying specimens

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 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)

Below are some examples of dichotomous keys represented as both diagrams and descriptions (click on image to swap):

Dichotomous Key:  Plant Phyla

Dichotomous Key:  Invertebrate Phyla


Dichotomous Key:  Vertebrate Classes

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