thumb|300px|In this [[phylogenetic tree, the blue and red groups (which are both monophyletic) do not share an immediate common ancestor. If they are grouped together because they share characteristics which appear to be similar, then their combination forms a polyphyletic group.]]

thumb|300px|[[Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly (the prosimians, in cyan, including the red patch), and a polyphyly (the night-active primates, the lorises and the tarsiers, in red).]]

thumbnail|300px|Phylogenetic groups: A monophyletic taxon (in yellow, the clade [[Sauropsida grouping "reptiles and birds") contains a common ancestor and all of its descendants. A paraphyletic taxon (in cyan, the "reptiles") contains its most recent common ancestor, but does not contain all the descendants of that ancestor. A polyphyletic taxon (in red, the group Haemothermia containing warm-blooded tetrapods) does not contain the most recent common ancestor of all its members.]]

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 homoplasies, which are explained as a result of convergent evolution. The arrangement of the members of a polyphyletic group is called a polyphyly . It is contrasted with monophyly and paraphyly.

For example, the biological characteristic of warm-bloodedness 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 slime molds, worms, algae, trees, C4 photosynthetic plants, and edentates.

Many taxonomists 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 barcoding of diverse groups of species.

Etymology

The term polyphyly, or polyphyletic, derives from the two Ancient Greek words () 'many, a lot of', and () 'genus, species', and refers to the fact that a polyphyletic group includes organisms (e.g., genera, species) arising from multiple ancestral sources.

Conversely, the term monophyly, or monophyletic, employs the ancient Greek adjective () 'alone, only, unique',

Polyphyletic species

Species have a special status in systematics as being an observable feature of nature itself and as the basic unit of classification. It is usually implicitly assumed that species are monophyletic (or at least paraphyletic). However, hybrid speciation arguably leads to polyphyletic species. Hybrid species are a common phenomenon in nature, particularly in plants where polyploidy allows for rapid speciation. Some cladist authors do not consider species to possess the property of "-phyly", which they assert applies only to groups of species.

See also

  • Carcinisation
  • Convergent evolution

References

Bibliography

  • Funk, D. J., and Omland, K. E. (2003). "Species-level paraphyly and polyphyly: Frequency, cause and consequences, with insights from animal mitochondrial DNA" Annu. Rev. Ecol. Evol. Syst. 34: 397–423. at ftp://137.110.142.4/users/bhhanser/Subspecies%20general%20literature/FunkEtal2003AnnuRevEcolEvolV34pp397-423.pdf