Dichotomous Key
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Identification of plants and animals in taxonomy is frequently aided by using a dichotomous key, a (usually written) device constructed from a series of highly organized statements arranged into couplets. A couplet consists of (typically) two descriptions which should represent mutually exclusive choices (often it is a particular combination of characteristics that determines the difference). Both choices are read and compared with the specimen to be identified. Having several individuals of the same species to observe is often helpful. Once a decision is made, that selection directs you to another couplet (either the next in order or one further on in the key), and this process is repeated until a conclusion (successful identification) is reached. At this point a verification step is important: compare the specimen with any details in the description and/or any available figures. Also consider habitat and location where the collection was made. If the description seems satisfactory, a correct identification probably has been achieved. If the description is not satisfactory in one or more important particulars, back up to some earlier couplet and start over, questioning each decision more carefully.
A very common error in using a dichotomous key is the assumption that the correct identification is even included in that key. It is possible that a specimen cannot be identified with a particular key, yet the key will lead the user to an end that appears to be the "answer". For this reason, comparing the specimen with a more detailed description is vitally important—a dichotomous key alone cannot be used to identify specimens, unless the specimens are known in advance to be included within the key.
There are dichotomous keys available on:
