monophyletic

In biological classification, term describing a group of species composed of an ancestral species plus all of its descendant species. Examples of such groups are the mammals, birds, and insects. Monophyletic groups, or clades, are the basis of the system of classification known as cladistics.

If a group does not include all the descendants of a common ancestor, it is called paraphyletic; if it includes some or all of the descendants but not the common ancestor, it is called polyphyletic.