monophyletic

adjective

(Gr. monos: alone; phylę: tribe) If the members of a given taxon are descended from a common ancestor they are said to be 'monophyletic', e.g. the families within a class would be monophyletic if they were all descended from the same family or lower taxonomic unit. Under the strictest definition they would all have to be descended from a single species. A monophyletic group is called a clade. Cf. polyphyletic.