subclade

Subclade is a term used in cladistics to denote a monophyletic subgroup within a larger clade. A clade is a group that includes a common ancestor and all its descendants. A subclade thus represents a more narrowly defined lineage nested within the larger clade, sharing a more recent common ancestor than the ancestor of the whole clade. Subclades are not formal taxonomic ranks; they are descriptive groupings that reflect evolutionary relationships.

Identification and evidence: Subclades are identified from phylogenetic trees generated from morphological data, DNA or protein sequences, or combined datasets. They are typically diagnosed by synapomorphies—shared derived characters that are present in all members of the subclade and absent in others. Boundaries of subclades can be revised as new data or methods refine the tree.

Relationship to classification: Because clades are monophyletic, any subclade within a clade is also monophyletic. A clade can contain many nested subclades, each defined at different levels of detail. In practice, the word subclade is used to describe groups without assigning formal taxonomic ranks, though some authors may use it to aid communication alongside named ranks.

Examples: In the vertebrate tree, Tetrapoda is a clade; Amniota is a subclade within Tetrapoda; within Amniota, Synapsida and Sauropsida are subclades that diverge toward mammals and reptiles/birds, respectively. Within Synapsida, Theria is a subclade; within Theria, Eutheria (placental mammals) and Metatheria (marsupials) are subclades. These examples illustrate how subclades organize evolutionary relationships without requiring formal ranks.