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Clade

A phylogenetic group generated by one ancestor and closed under descent: it contains that ancestor and every descendant, irrespective of rank, resemblance, or survival to the present.

Version
v3 · 2026-09-19 · History
Domain-specific #
1473
Domain group
Natural Sciences
Origin domain
Biology & Ecology
Subdomains
Biological Systematics, Phylogenetic Classification → Biology & Ecology
Aliases
Monophyletic Group

Core Idea

A clade is a phylogenetic group generated by one ancestor and closed under descent: it contains the ancestor and every organism, population, species, or lineage descended from that ancestor. The International Code of Phylogenetic Nomenclature gives this ancestor-plus-all-descendants identity as the defining content of a clade. In contemporary biological usage, monophyletic group is an equivalent term. The definition classifies membership by ancestry, not by visual resemblance, ecological role, taxonomic rank, age, abundance, or whether a member survives today.

Let \(T=(V,E,r)\) be a rooted phylogenetic tree or a rooted hypothesis of lineage history. Write \(u\preceq_T v\) when \(u=v\) or a directed path of descent runs from \(u\) to \(v\).

How would you explain it like I'm…

A Whole Family Branch

A clade is like a whole family tree branch: one great-great-grandparent and every single person who came from them, with nobody left out. Scientists use it for animals and plants. Even if some of the family look totally different or have died out, they still belong on the branch.

Ancestor Plus Everyone After

In biology, a clade is a group made of one ancestor and all of its descendants, every last one. Scientists draw family trees of living things, and a clade is a whole branch cut off from the tree at one point. You can't leave anyone out: if a descendant is missing, it's not a clade. And being in the group depends only on who you came from, not on how you look or live, so a descendant that looks very different still belongs, and so do ones that went extinct. Another name for a clade is a monophyletic group.

Monophyletic Group

A clade, also called a monophyletic group, is a group of organisms or lineages containing one ancestor and all of its descendants. On a phylogenetic tree (a diagram of evolutionary descent), you can find a clade by picking a point on the tree and taking everything that branches off after it. The test is strict: if even one descendant is left out, the group is not a clade. Membership depends only on ancestry, not on looks, lifestyle, rank, age, or whether the organisms are still alive. It's important to separate two things: the real history of descent, and the trees scientists infer from data. Different data or methods can produce different trees and therefore different clade assignments; the definition tells you how to recognize a clade, but it doesn't make every published tree correct. Also, flipping branches in a drawing changes the picture but not which groups are clades.

 

A clade is a phylogenetic group generated by one ancestor and closed under descent: it includes that ancestor and every organism, population, species, or lineage descended from it. The International Code of Phylogenetic Nomenclature takes this ancestor-plus-all-descendants definition as defining, and 'monophyletic group' is an equivalent term. Formally, on a rooted tree T, the clade generated by a node a is the set of all nodes v such that v is a or descends from a; a proposed group G is a clade exactly when G equals that set for some a. Its defining invariant is descendant closure: if v is in the clade and w descends from v, then w is too. So 'an ancestor plus selected descendants' is not enough, and a descendant that looks or lives differently still belongs; extinct members count as well. Clades are read from branching topology, not from ladder-like tip order, so branch rotations don't change membership. The historical clade must be distinguished from an empirical clade assignment made on an inferred tree, since different data, sampling, rooting, or methods can yield different trees.

Scope of Application

Clade is native to biological systematics and phylogenetics. Systematists use it to delimit groups, interpret character evolution, compare classifications with phylogenetic hypotheses, and formulate rank-independent names. The same role structure occurs at multiple biological scales: species and higher lineages in organismal phylogenies, gene copies in gene trees, viral sequences in transmission or evolutionary trees, and populations in within-species histories. Every use must name the lineage-bearing unit and the tree or historical scope.

Clarity

Clade turns an ambiguous phrase such as “natural group” into an auditable membership test. Ask four questions: What is the lineage-bearing unit? What rooted phylogeny is being used? Which ancestor generates the group? Does the group include every descendant in scope? A yes to all four establishes a clade relative to the stated tree. Failure on the final question identifies paraphyly; assembling tips without the corresponding ancestral branch identifies polyphyly.

Manages Complexity

Phylogenies can contain thousands or millions of terminals. Clades compress this branching complexity into reusable descendant-closed units. Once a node has been identified, the analyst need not enumerate each descendant whenever discussing a shared history; the generator and closure rule determine the group. Nestedness also supports multiscale reasoning: a small clade can be analyzed within a larger clade without losing the ancestry relation connecting them.

Abstract Reasoning

Clade reasoning begins with descendant closure rather than resemblance. Given a rooted tree, select a candidate ancestor and trace every outgoing descent path. The union of the ancestor and everything reached is a clade. To test a proposed group, compute its most recent common ancestor and inspect every descendant branch. If any descendant lies outside the proposal, the proposal is not monophyletic on that tree.

Knowledge Transfer

Within biology, the role mapping travels cleanly from organismal systematics to gene-family analysis, viral evolution, paleontology, and population history:

  • ancestral species or population \(\leftrightarrow\) ancestral gene copy or viral lineage;
  • organismal descendants \(\leftrightarrow\) descendant copies, sequences, or transmission lineages;
  • rooted species tree \(\leftrightarrow\) rooted gene, virus, or population tree;
  • taxon sampling \(\leftrightarrow\) sequence or isolate sampling;
  • monophyly test \(\leftrightarrow\) complete descendant-branch test at the declared scale.

Relationships to Other Abstractions

Local relationship map for CladeParents appear above the current abstraction, mutual partners to the right, and children below. Node labels state whether each abstraction is prime or domain-specific; colors identify relation types.CladeDOMAINPrime abstraction: Closure — is a kind ofClosurePRIME

Current abstraction Clade Domain-specific

Parents (1) — outgoing typed relations

  • Clade is a kind of Closure Prime

    Closure is the closest structural parent.

Hierarchy path (1) — routes to 1 parentless root

Neighborhood in Abstraction Space

Clade sits in a sparse region of the domain-specific corpus (85th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.

Family — Unclustered & Miscellaneous (2769 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-25