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BIOL 201: Dichotomous Key Lab
• Taxonomy is the science dealing with description, identification,
nomenclature, and classification of living things.
• A dichotomous key is a tool that allows users to identify items or
organisms in a systematic and reproducible fashion.
• Dichotomous keys may be used in a variety of situations, such as for
identifying rocks and minerals as well as for identifying unknown
organisms to some taxonomic level (e.g., species, genus, family, etc.).
• What makes these keys distinctive is that they are ordered in such a way
that a series of choices is made that leads the user to the correct identity
of the item they are looking at. If the user makes the correct choice every
time, the name of the organism will be revealed at the end.
• "Dichotomous" means, "divided into two parts." Therefore, dichotomous
keys always offer two choices for each step, each of which describes key
characteristics of a particular organism or group of organisms.
• There are two kinds of descriptions that might be presented to the user of
a dichotomous key: qualitative and quantitative descriptions.
1. Qualitative descriptions concern the physical attributes, or qualities, of
the item being classified. Examples of qualitative descriptions are such
phrases as "contains green striations on top surface" or "feels slick on
bottom surface."
2. Quantitative descriptions concern values that correspond with the item
being classified. Examples of quantitative descriptions are such phrases
as "has 10 striations on top surface," "has 8 legs," or "weighs 5 grams".
Knowing the difference between these two types of descriptions can be
immensely beneficial for creators and users of dichotomous keys.
• You simply compare the characteristics of an unknown organism against
an appropriate dichotomous key. These keys will begin with general
characteristics and lead to couplets indicating progressively specific
characteristics.
