Paraphyletic
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A taxon is said to be paraphyletic if it does not contain all descendants of its last common ancestor. So, for example, "seedless plants" is paraphyletic because its last common ancestor would also be the ancestor of plants with seeds. A clade must contain all descendants of its last common ancestor. It is usually fairly important to stick to a consideration of clades. However, that importance can often be outweighed by the utility of being able to discuss the earliest forms of some group. We normally signal that we are talking about such a paraphyletic group by saying "basal seedless plants" or "paraphyletic seedless plants" or by the use of some other, similar linguistic artifice.
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