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A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, which are explained as a result of convergent evolution. The arrangement of the members of a polyphyletic group is called a polyphyly .. Source It is contrasted with monophyly and paraphyly.
For example, the biological characteristic of evolved separately in the ancestors of mammals and the ancestors of birds; "warm-blooded animals" is therefore a polyphyletic grouping. Other examples of polyphyletic groups are algae, C4 photosynthetic plants, and edentates. (2025). 9780813031651, University Press of Florida. ISBN 9780813031651
Many aim to avoid homoplasies in grouping taxa together, with a goal to identify and eliminate groups that are found to be polyphyletic. This is often the stimulus for major revisions of the classification schemes. Researchers concerned more with ecology than with systematics may take polyphyletic groups as legitimate subject matter; the similarities in activity within the fungus group Alternaria, for example, can lead researchers to regard the group as a valid genus while acknowledging its polyphyly. In recent research, the concepts of monophyly, paraphyly, and polyphyly have been used in deducing key genes for DNA barcoding of diverse groups of species.
Conversely, the term monophyly, or monophyletic, employs the ancient Greek adjective () 'alone, only, unique', and refers to the fact that a monophyletic group includes organisms consisting of all the descendants of a unique common ancestor.
By comparison, the term paraphyly, or paraphyletic, uses the ancient Greek preposition () 'beside, near', and refers to the situation in which one or several monophyletic subgroups are left apart from all other descendants of a unique common ancestor.
From a practical perspective, grouping species monophyletically facilitates prediction far more than does polyphyletic grouping. For example, classifying a newly discovered grass in the monophyletic family Poaceae, the true grasses, immediately results in numerous predictions about its structure and its developmental and reproductive characteristics, that are synapomorphies of this family. In contrast, Linnaeus' assignment of plants with two to the polyphyletic class Diandria, while practical for identification, turns out to be useless for prediction, since the presence of exactly two stamens has developed convergently in many groups.
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