Aphylogenetic tree: both blue and red groups aremonophyletic. The green group isparaphyletic: it is missing a monophyletic subgroup – the blue group – that shares a common ancestor with itself. In this form,monophyletic means "no sideways stems leaving the group".A cladogram of theprimates, showing amonophyletic taxon: thesimians (in yellow); aparaphyletic taxon: theprosimians (in cyan, including the red patch); and apolyphyletic group:the night-active primates, i.e., thelorises and thetarsiers (in red).A cladogram of the vertebrates showing phylogenetic groups. Amonophyletictaxon (in yellow):the group of "reptiles and birds", contains its most recent common ancestor and all descendants of that ancestor. Aparaphyletic taxon (in cyan):the group of reptiles, contains its most recent common ancestor, but does not contain all the descendants (namely Aves) of that ancestor. Apolyphyletic "group" (in red):the group ofall warm-blooded amniotes (Aves and Mammalia), does not contain the most recent common ancestor of all its members; this group is not seen as a taxonomic unit and is not considered a taxon by modernsystematists.
In biologicalcladistics for the classification oforganisms,monophyly is the condition of ataxonomic grouping being aclade – that is, a grouping of organisms which meets these criteria:
the grouping contains its own most recent common ancestor (or more precisely an ancestralpopulation), i.e. excludes non-descendants of that common ancestor
the grouping contains all the descendants of that common ancestor, without exception
Monophyly is contrasted withparaphyly andpolyphyly as shown in the second diagram. Aparaphyletic grouping meets 1. but not 2., thus consisting of the descendants of a common ancestor, excepting one or more monophyletic subgroups. Apolyphyletic grouping meets neither criterion, and instead serves to characterizeconvergent relationships of biological features rather than genetic relationships – for example, night-active primates, fruit trees, or aquatic insects. As such, these characteristic features of a polyphyletic grouping are not inherited from a common ancestor, but evolved independently.
Monophyletic groups are typically characterised by shared derived characteristics (synapomorphies), which distinguish organisms in the clade from other organisms. An equivalent term isholophyly.[1]
The word "mono-phyly" means "one-tribe" in Greek.
These definitions have taken some time to be accepted. When the cladistics school of thought became mainstream in the 1960s, several alternative definitions were in use. Indeed,taxonomists sometimes used terms without defining them, leading to confusion in the early literature,[2] a confusion which persists.[3]
The first diagram shows aphylogenetic tree with two monophyletic groups. The several groups and subgroups are particularly situated as branches of the tree to indicate ordered lineal relationships between all the organisms shown. Further, any group may (or may not) be considered ataxon by modernsystematics, depending upon the selection of its members in relation to their common ancestor(s); see second and third diagrams.
The termmonophyly, ormonophyletic, derives from the twoAncient Greek wordsμόνος (mónos), meaning "alone, only, unique", andφῦλον (phûlon), meaning "genus, species",[4][5] and refers to the fact that a monophyletic group includes organisms (e.g., genera, species) consisting of all the descendants of aunique common ancestor.
Conversely, the termpolyphyly, orpolyphyletic, builds on the ancient Greek prefixπολύς (polús), meaning "many, a lot of",[4][5] and refers to the fact that a polyphyletic group includes organisms arising frommultiple ancestral sources.
By comparison, the termparaphyly, orparaphyletic, uses the ancient Greek prefixπαρά (pará), meaning "beside, near",[4][5] and refers to the situation in which one or several monophyletic subgroups areleft apart from all other descendants of a unique common ancestor. That is, a paraphyletic group isnearly monophyletic, hence the prefixpará.
On the broadest scale, definitions fall into two groups.
Willi Hennig (1966:148) defined monophyly as groups based onsynapomorphy (in contrast to paraphyletic groups, based onsymplesiomorphy, and polyphyletic groups, based onconvergence). Some authors have sought to define monophyly to include paraphyly as any two or more groups sharing a common ancestor.[3][6][7][8] However, this broader definition encompasses both monophyletic and paraphyletic groups as defined above. Therefore, most scientists today restrict the term "monophyletic" to refer to groups consisting of all the descendants of one (hypothetical) common ancestor.[2] However, when considering taxonomic groups such as genera and species, the most appropriate nature of their common ancestor is rather a population. Assuming that it would be one individual or mating pair is unrealistic for sexually reproducing species, which are by definition interbreeding populations.[9]
Monophyly (or holophyly) and associated terms are restricted to discussions of taxa, and are not necessarily accurate when used to describe what Hennig called tokogenetic relationships – now referred to as genealogies. Some argue that using a broader definition, such as a species and all its descendants, does not really work to define a genus.[9] The loose definition also fails to recognize the relations of all organisms.[10] According to D. M. Stamos, a satisfactory cladistic definition of a species or genus is impossible because many species (and even genera) may form by "budding" from an existing species, leaving the parent species paraphyletic; or the species or genera may be the result ofhybrid speciation.[11]
The concepts of monophyly,paraphyly, andpolyphyly have been used in deducing key genes forbarcoding of diverse group of species.[12]
^Allaby, Michael (2015).A Dictionary of Ecology (5 ed.). Oxford: Oxford University Press.ISBN9780191793158.
^abHennig, Willi (1999) [1966].Phylogenetic Systematics. Translated by Davis, D.; Zangerl, R. (Illinois Reissue ed.). Board of Trustees of the University of Illinois. pp. 72–77.ISBN978-0-252-06814-0.
^abAubert, D. 2015. A formal analysis of phylogenetic terminology: Towards a reconsideration of the current paradigm in systematics.Phytoneuron2015-66:1–54.
^Parhi J., Tripathy P.S., Priyadarshi, H., Mandal S.C., Pandey P.K. (2019). "Diagnosis of mitogenome for robust phylogeny: A case of Cypriniformes fish group".Gene.713: 143967.doi:10.1016/j.gene.2019.143967.PMID31279710.S2CID195828782.{{cite journal}}: CS1 maint: multiple names: authors list (link)
