Clades and rooted-tree interpretation
Shared ancestry is represented by topology, not by the left-to-right order of tips.
Key knowledge
In a rooted evolutionary tree, a clade contains an ancestral lineage and all its represented descendants. Sister lineages share an immediate common ancestral node in that tree. Rotating branches around a node preserves ancestry relationships; neighboring tip positions alone do not establish closer relationship. Branch lengths represent time or change only when the tree's scale explicitly says so.
Conditions and scope
- Specify whether the diagram is rooted and whether it has a branch-length scale; a tree is an inferred hypothesis rather than a direct record of every ancestor.
- An unrooted tree does not identify an ancestral direction. Reticulate histories such as hybridization may require networks rather than one bifurcating tree.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Mary Ann Clark, Matthew Douglas and Jung Choi · OpenStax/Rice University2 sources
Evidence and review
Inspected §20.1 root/node/sister-lineage and branch-rotation discussion and §20.2 clade definition. Excludes primitive-living-lineage implications and assumptions that every displayed branch is a dated interval.
2026-10-10 · Independent Mathematics and Information editor (/root/core_math_information). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
Entry details
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- foundation-bio-clades-tree-reading
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- foundations-refresh.1
- Structured reference record
- Foundational reference additions