A clade is a term belonging to the discipline of cladistics. For all practical purposes it will usually refer to : This cladogram shows the relationship among various insect groups. ...
a branch in a cladogram, which is a diagram in the form of a tree resulting from a cladistic analysis.
a monophyletic group of organisms, i.e. a group of organisms which share a common ancestor and which includes the ancestor and all the descendents of that ancestor.
Strictly speaking, a clade is a scientific hypothesis of evolutionary relationships among the organisms included in the analysis, based on the data considered in a cladistic analysis. Therefore, it will depend upon the data used to produce it; a particular clade may be supported or disproved by a subsequent analysis using different data. Greek clados = branch) or phylogenetic systematics is a branch of biology that determines the evolutionary relationships of living things based on derived similarities. ... In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ... In biology and ecology, an organism (in Greek organon = instrument) is a living being. ...
If a clade proves robust in different analyses using different kinds of data, it may be translated to taxonomy: it will become a taxon, and may get a formal name and a rank. The idea that all taxa should be clades enjoys widespread support, but it remains controversial. A clade may or may not conform to an existing taxon, and vice versa: see also grade. Taxonomy, sometimes alpha taxonomy, is the science of finding, describing and naming organisms, thus giving rise to taxa. ... A taxon (plural taxa), or taxonomic unit, is a grouping of organisms (named or unnamed). ... In phylogenetics, a grouping of organisms is said to be paraphyletic (Greek para = near and phyle = race) if the group contains the most recent common ancestor of its members, but the group does not include all the descendants of this common ancestor. ...
The PhyloCode is an attempt at a Code that would allow clades to get a formal name. Types of clade PhyloCode is a draft for a formal set of rules governing phylogenetic nomenclature. ...
Each clade is set off by a series of characteristics that appear in its members, but not in the other forms from which it diverged.
Stem-based: all descendants of the oldest common ancestor of A and B that is not also an ancestor of Z. Apomorphy-based: the most recent common ancestor of A and B possessing a certain apomorphy (derived character), and all its descendants.
A monophyletic group is a clade, comprising an ancestral form and all of its descendants, and so forming one (and only one) evolutionary group.
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