A polyphyletic group is a series of organisms or other developing elements that have been grouped together on the basis of characteristics that do not imply that they have a common ancestor that is not also the common ancestor of many other taxa (of course, if “life “is monophyletic, then each group of organisms shares a common ancestor at some point in the root of the tree).
The term is also applied to those groups that share characteristics that appear to be similar but have not been inherited from common ancestors these characteristics are known as homoplasies.
And the development and phenomenon of homoplasies are known as convergent evolution. The arrangement of the members of a polyphyletic group is called polyphyly. Alternatively, polyphyletic is simply used to describe a group whose members come from multiple ancestral sources, regardless of the similarity of characteristics.
For example, the biological characteristic of warm-bloodedness evolved separately in the ancestors of mammals and the ancestors of birds. Other polyphyletic groups are for example algae, C4 photosynthetic plants, and edentates. Many biologists try to avoid homoplasies in grouping taxa, and therefore it is often a goal to eliminate groups that turn out to be polyphyletic.
This is often the incentive for major revisions to the classification schemes. Researchers more concerned with ecology than systematics may consider polyphyletic groups as a legitimate subject. the similarities in activity within the Alternaria fungal group.
For example, can lead researchers to regard the group as a valid genus while recognizing its polyphyly. In recent research, the concepts of monophyly, paraphyly, and polyphyly have been used in deducing key genes for the barcoding of diverse groups of species.
The term polyphyly or polyphyletic is derived from the two ancient Greek words polús, which means “many”, and phûlon, which means “genus, species“, and refers to the fact that a polyphyletic group of organisms (e.g. Genera. species) from several ancestral sources.
Conversely, the term monophyly, or monophyletic, builds on the ancient Greek prefix mónos, meaning “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 prefix pará, meaning “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.
In many schools of taxonomy, the existence of polyphyletic groups in classification is discouraged. Monophyletic groups (that is, clades) are considered by these schools of thought to be the most important grouping of organisms.
One reason for this view is that some classes can be simply defined purely phylogenetically, without reference to previously introduced classes: a node-based clade definition.
For example, “all descendants of the last common ancestor of species X and Y” could be. On the other hand, polyphyletic groups can often be delimited in relation to clades, for example, “the flying vertebrates consist of a bat, bird, and pterosaur clades”.
Because polyphyletic groups can frequently be defined as a sum of clades, they are usually considered less fundamental than monophyletic (single, whole) clades. A stronger reason is that 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, inherited from the common ancestor of this family.
In contrast, Linnaeus’ assignment of plants with two stamens to the polyphyletic class Diandria, although practical for identification, proves useless for prediction, since the presence of exactly two stamens has developed converging in many groups. Predictive success is the touchstone against which theories are evaluated in all experimental sciences.
In the system, species have a special status as an observable feature of nature itself and as a basic classification unit. It is usually implicitly assumed that species are monophyletic (or at least paraphyletic). However, hybrid speciation may lead to polyphyletic species. Hybrid species are a common phenomenon in nature, especially in plants where polyploidy enables rapid speciation