Biology – 1.2 Concept and uses of classification systems | e-Consult

A taxonomic key is a tool used to identify organisms by comparing their characteristics to a series of paired statements. It's a practical tool for identifying organisms in the field. It typically presents a series of choices, leading the user to a specific identification. For example: "Does the organism have spines? If yes, go to statement 2. If no, go to statement 3."

A cladogram, on the other hand, is a diagrammatic representation of evolutionary relationships. It shows the branching pattern of a phylogeny, indicating how different groups of organisms are related to each other. The branches represent evolutionary lineages, and the nodes represent common ancestors. Cladograms are based on shared derived characteristics (synapomorphies).

Both taxonomic keys and cladograms are used in classification systems, but for different purposes. A taxonomic key helps to assign an individual organism to a specific taxonomic group based on its observable characteristics. A cladogram helps to understand the evolutionary relationships between different groups of organisms and to construct a classification system that reflects those relationships. Modern classification systems increasingly rely on cladograms to ensure that groups are based on evolutionary history, not just superficial similarities. A taxonomic key might be *derived from* a cladogram, using the characteristics identified in the cladogram to create the key's statements.