CoachA group is monophyletic (a clade) if it contains an ancestor and all its descendants; paraphyletic if it contains an ancestor and only some of its descendants (the “reptiles”, which exclude the birds descended from them; the “fish”, which exclude the tetrapods; the “invertebrates”); polyphyletic if it groups descendants of different ancestors by a convergent character (the “warm-blooded animals”, birds and mammals; the “algae”). Paraphyletic groups are useful descriptions of grades of organisation but are not clades and are no longer given formal names.
