Phylogenetic tree

Definition

A branching diagram that depicts the evolutionary relationships among taxa based on shared ancestry, inferred from morphological, molecular, or behavioral data. Each node represents a hypothetical common ancestor; branches indicate lineage divergence through time. In entomology and arachnology, phylogenetic trees resolve debates about whether similar traits (e.g., silk production, eusociality, parasitoid life history) evolved once or repeatedly, and they underpin modern classification systems that aim to reflect monophyletic groups rather than superficial similarity.

Etymology

Greek phylon (tribe, race) + genetikos (origin) + Old English treow (tree)

Example

Molecular phylogenetic trees based on ribosomal RNA sequences revealed that the order Psocodea (barklice and booklice) is the sister group to Phthiraptera (lice), leading to their merger into a single order and overturning the traditional view that lice were unrelated to psocids.

Synonyms

• Phylogeny
• cladogram (when topology only, no branch lengths)
• tree of life (broadly)

Related Terms

• clade
• monophyly
• paraphyly
• polyphyly
• synapomorphy
• Convergent evolution
• molecular phylogenetics
• maximum likelihood
• Bayesian inference
• bootstrap support

Usage Notes

Specialists distinguish between a cladogram (branching order only), phylogram (branch lengths proportional to change), and chronogram (branches scaled to time). "Phylogeny" sometimes refers to the tree itself, sometimes to the evolutionary history it represents. Trees are hypotheses, not facts; conflicting topologies between morphological and molecular datasets remain common in arthropod systematics, especially for rapid radiations like early insects or spiders.