Identification Key: Definition & Examples

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An identification key is an identification tool primarily used to find taxonomic levels (e.g. species or genus) in the biological sciences. The keys have a wide variety of applications, including identification of plants, nuts, and amphibians as well as in forensic analysis.

As an example, let’s say you found a moth in the Dakotas, and you wanted to know if it belonged to the butterflies, primitive moths, or other groups. You might be tempted to compare your moth to online pictures, but there are over 1,400 species of moth in the Dakotas. An identification key helps by taking your through a series of steps to identify the group. Some keys, like this Purdue University field guide, use a combination of pictures and words.

identification key
Step 3 from a Purdue University field guide to identifying larval amphibians.

Dichotomous Identification Key

Dichotomous keys provide a set of two alternatives. You’re given two descriptions at each step, simply choosing the one which fits best. The Cortland Herpetology Connection offers this example for a dichotomous identification key: let’s say you wanted to identify a certain reptile/amphibian from New York state and you want to classify it as belonging to frogs, salamanders, snakes and lizards, or turtles. The first step might ask:
External gills?
If yes, it’s a salamander. If no, go to the next question. Each subsequent question would provide a binary option.


N, Talent et al. (2014). Character Selection During Interactive Taxonomic Identification. Biodiversity Informatics.
Cortland Herpetology Connection. How to use the identification keys. Retrieved August 12, 2019 from:
North Dakota State University. Identification Key. Retrieved August 12, 2019 from:
Randler, C. (2008). Teaching Species Identification – A Prerequisite for Learning Biodiversity and Understanding Ecology. Eurasia Journal of Mathematics, Science & Technology Education.

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