Composed of members which all originated from a single ancestral line, which is included in the taxonomic group, but where the ancestor also has (or had) other descendents not within the group. For example, all cats are within the taxonomic group of carnivores, but not all carnivores are cats. Compare with
monophyletic and polyphyletic.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.