Evolutionary taxonomy or evolutionary systematics seeks to classify organisms using a combination of phylogenetic relationship and overall similarity. It differs from strict cladism where all taxa in a classification always should include all descendants of a single ancestral node. It thus allows for paraphyletic taxa. As evolutionary systematicists define terms, paraphyletic taxa are monophyletic too, in the sense that they derive from a single common ancestor, just not holophyletic, meaning that all descendants are included (which is monophyletic according to the cladistic definition).