Cladogram

Definition

A branching diagram that depicts hypothesized evolutionary relationships among groups of organisms based on shared derived characters (synapomorphies). Unlike many phylogenetic trees, cladograms do not necessarily represent evolutionary time or the amount of morphological change; they show only the relative recency of common ancestry. In arthropod systematics, cladograms are used to test competing hypotheses about the relationships among insect orders, the placement of arachnid orders, or the monophyly of major clades such as Hexapoda or Chelicerata.

Etymology

From Greek klados (branch) + gramma (letter, drawing)

Example

A cladogram of Hymenoptera might show ants (Formicidae) and vespid wasps as sister groups based on the shared derived trait of a constricted petiole (wasp waist), while sawflies branch more basally due to the absence of this feature.

Synonyms

• cladistic tree
• phylogram (when branch lengths represent change)

Related Terms

• Cladistics
• synapomorphy
• Phylogenetic tree
• node
• branch
• outgroup
• monophyly
• Parsimony
• Phylogeny

Usage Notes

Cladogram is often used more strictly than phylogenetic tree: some systematists reserve cladogram for diagrams where branch lengths are arbitrary and only topology matters, whereas phylograms or chronograms convey additional information about evolutionary distance or time. In practice, the terms overlap considerably. Cladograms are constructed using parsimony, maximum likelihood, or Bayesian methods, with molecular data increasingly supplementing or replacing morphological characters in arthropod phylogenetics.