Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
A basal taxon is a lineage that diverges early in the history of a group and remains unbranched. It is often used as a reference point to understand evolutionary relationships within a clade.
5 Must Know Facts For Your Next Test
A basal taxon appears at the base of a phylogenetic tree.
Basal taxa are important for understanding the ancestral traits of a group.
They help illustrate how different lineages have evolved over time.
A basal taxon does not imply primitiveness but indicates an early branch in evolutionary history.
Outgroup species are often chosen from basal taxa to root phylogenetic trees.
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Related terms
clade: A group of organisms believed to have evolved from a common ancestor, according to the principles of cladistics.
outgroup: A species or group that is closely related to the ingroup but not part of it, used as a reference point in phylogenetic analysis.
A branching diagram showing the inferred evolutionary relationships among various biological species based upon similarities and differences in their physical or genetic characteristics.