In cladistics, a monophyletic group, or clade, is a group of organisms that consists of all the descendants of a common ancestor (or more precisely ancestral population). Monophyletic groups are typically characterised by shared derived characteristics (synapomorphies), which distinguish organisms in the clade from other organisms. The arrangement of the members of a monophyletic group is called a monophyly.
Monophyly is contrasted with paraphyly and polyphyly as shown in the second diagram. A paraphyletic group consists of all of the descendants of a common ancestor minus one or more monophyletic groups. A polyphyletic group is characterized by convergent features or habits of scientific interest (for example, night-active primates, fruit trees, aquatic insects). The features by which a polyphyletic group is differentiated from others are not inherited from a common ancestor.
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, a confusion which persists.
The first diagram shows a phylogenetic 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 a taxon by modern systematics, depending upon the selection of its members in relation to their common ancestor(s); see second and third diagrams.
The term monophyly, or monophyletic, derives from the two Ancient Greek words μόνος (mónos), meaning "alone, only, unique", and φῦλον (phûlon), meaning "genus, species", and refers to the fact that a monophyletic group includes organisms (e.g., genera, species) consisting of all the descendants of a unique common ancestor.
Conversely, the term polyphyly, or polyphyletic, builds on the ancient greek prefix πολύς (polús), meaning "many, a lot of",, and refers to the fact that a polyphyletic group includes organisms arising from multiple ancestral sources.
By comparison, the term paraphyly, or paraphyletic, uses the ancient greek prefix παρά (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. That is, a paraphyletic group is nearly monophyletic, hence the prefix pará.
On the broadest scale, definitions fall into two groups.
The Actinidiaceae are a small family of flowering plants commonly known as the Chinese gooseberry family. The family has three genera and about 360 species and is a member of the order Ericales.Aequornithes
Aequornithes (from Latin aequor, expanse of water + Greek ornithes, birds), or core water birds are defined as "the least inclusive clade containing Gaviidae and Phalacrocoracidae".The monophyly of the group is currently supported by several molecular phylogenetic studies.Aequornithes includes the clades Gaviiformes, Sphenisciformes, Procellariiformes, Ciconiiformes, Suliformes and Pelecaniformes. It does not include several unrelated groups of aquatic birds such as flamingos and grebes (Mirandornithes), shorebirds and auks (Charadriiformes), or the Anseriformes.
Based on a whole-genome analysis of the bird orders, the kagu and sunbittern (Eurypygiformes) and the three species of tropicbirds (Phaethontiformes) together styled as the Eurypygimorphae are the closest sister group of the Aequornithes in the clade Ardeae.
Cladogram based on Burleigh, J.G. et al. (2015)Atheriniformes
The Atheriniformes, also known as the silversides, are an order of ray-finned fishes that includes the Old World silversides and several less-familiar families, including the unusual Phallostethidae. The order includes at least 354 species. They are found worldwide in tropical and temperate marine and freshwater environments.Austrochilidae
Austrochilidae is a small spider family with ten species in three genera. Austrochilus and Thaida are endemic to the Andean forests of central and southern Chile and adjacent Argentina, while Hickmania is endemic to Tasmania. The monophyly of the family and the relationships among the genera are uncertain as of May 2017.Claroteidae
The Claroteidae are a family of catfish (order Siluriformes) found in Africa. This family was separated from Bagridae. However, the monophyly of the family is sometimes contested.The 12 genera contain 86 known species of claroteids in two subfamilies, Claroteinae and Auchenoglanidinae. The subfamily Auchenoglanidinae is sometimes classified as a separate family Auchenoglanididae. This group was also often formerly placed in Bagridae. The monophyly of Auchenoglanidinae is uncontested; it contains the three genera Auchenoglanis, Parauchenoglanis and Notoglanidium.Two commonly known species are the giraffe catfish, Auchenoglanis occidentalis, and the African big-eye catfish, Chrysichthys longipinnis.
Claroteids have moderately elongated bodies, usually with four pairs of barbels, an adipose fin, and strong pectoral and dorsal fin spines.Crambinae
Crambinae is a large subfamily of the lepidopteran family Crambidae, the crambid snout moths. It currently includes over 1,800 species worldwide. The larvae are root feeders or stem borers, mostly on grasses. A few species are pests of sod grasses, maize, sugar cane, rice, and other Poaceae. The monophyly of this group is supported by the structure of the tympanal organs and the phallus attached medially to the juxta.
Taxonomists' opinions differ as to the correct placement of the Crambidae, some authorities treating them as a subfamily of the family Pyralidae. If this is done, the present group would be demoted to tribe status, as Crambini.Entelegynae
The Entelegynae or entelegynes are a subgroup of araneomorph spiders, the largest of the two main groups into which the araneomorphs were traditionally divided. Females have a genital plate (epigynum) and a "flow through" fertilization system; males have complex palpal bulbs. Molecular phylogenetic studies have supported the monophyly of Entelegynae (whereas the other traditional subgroup, the Haplogynae, has been shown not to be monophyletic).The clade contains both cribellate and ecribellate spiders.Eumetabola
Eumetabola is an unranked category of Neoptera. Two large unities known as the Paurometabola and Eumetabola are probably from the adelphotaxa of the Neoptera after exclusion of the Plecoptera. The monophyly of these unities appears to be weakly justified.Excavata
Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. Introduced by Thomas Cavalier-Smith in 2002 as a new phylogenetic category, it contains a variety of free-living and symbiotic forms, and also includes some important parasites of humans, including Giardia and Trichomonas. Excavates were formerly considered to be included in the now obsolete Protista kingdom. They are classified based on their flagellar structures, and they are considered to be the most basal Flagellate lineage. Except for Euglenozoa, they are all non-photosynthetic.Genus
A genus (, pl. genera ) is a taxonomic rank used in the biological classification of living and fossil organisms, as well as viruses, in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.
E.g. Panthera leo (lion) and Panthera onca (jaguar) are two species within the genus Panthera. Panthera is a genus within the family Felidae.The composition of a genus is determined by a taxonomist. The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful:
monophyly – all descendants of an ancestral taxon are grouped together (i.e. phylogenetic analysis should clearly demonstrate both monophyly and validity as a separate lineage).
reasonable compactness – a genus should not be expanded needlessly; and
distinctness – with respect to evolutionarily relevant criteria, i.e. ecology, morphology, or biogeography; DNA sequences are a consequence rather than a condition of diverging evolutionary lineages except in cases where they directly inhibit gene flow (e.g. postzygotic barriers).Moreover, genera should be composed of phylogenetic units of the same kind as other (analogous) genera.Glires
Glires (Latin glīrēs, dormice) is a clade (sometimes ranked as a grandorder) consisting of rodents and lagomorphs (rabbits, hares, and pikas). The hypothesis that these form a monophyletic group has been long debated based on morphological evidence. Two morphological studies, published in 2001 and 2003, strongly support the monophyly of Glires. In particular, the 2003 study, reported the discovery of fossil material of basal members of Glires, particularly the genera Mimotona, Gomphos, Heomys, Matutinia, Rhombomylus, and Sinomylus. Their description, in 2005, helped to bridge the gap between more typical rodents and lagomorphs. Data published in 2001, based on nuclear DNA, supported Glires as a sister of Euarchonta to form Euarchontoglires, but some genetic data from both nuclear and mitochondrial DNA have been less supportive. A study, published in 2007, investigating retrotransposon presence/absence data unambiguously supports the Glires hypothesis. Studies published in 2011 and 2015 place Scandentia as a sister clade of the Glires, invalidating Euarchonta as a clade.Neoophora
Neoophora is a group of rhabditophoran flatworms with ectolecithal eggs, i.e., yolk is not present in the egg as in most animals, but rather is secreted by accessory glands called vitellaria or yolk glands. These glands have the same embryonic origin as the ovaries, but usually constitute a separate organ in adult animals.The monophyly of Neoophora is disputed, since some recent molecular studies indicated that the most basal order, Lecithoepitheliata, is more closely related to Polycladida, a non-neoophoran order, than to other neoophorans. This would imply that the ectolecithal condition would have evolved twice. The clade formed by all other neoophorans, excluding Lecithoepitheliata, is usually called Euneoophora.Orthopterida
The Orthopterida is a superorder of the Polyneoptera that represents the extant orders Orthoptera (grasshoppers, crickets, and katydids), and Phasmatodea (stick insects and leaf insects). The Orthopterida also includes the extinct orders Titanoptera and Caloneurodea. There is general consensus of monophyly in this superorder, based on reduction of the second valvulae, an ovipositor derived from the gonoplac, and an enlarged precostal region on the forewing.
The two other superorders of the Polyneoptera are the Plecopterida, which represents the orders Plecoptera (stoneflies), Emboidea (Embioptera/Embiidina; webspinners), and Zoraptera (angel insects), and the Dictyoptera, which represents Blattodea (cockroaches & termites), and Mantodea (mantids). Two other orders, the Notoptera (ice-crawlers and gladiators) and Dermaptera (earwigs) are also placed in the Polyneoptera but outside the superorders discussed above.Panorpida
Panorpida or Mecopterida is a proposed superorder of Endopterygota. The conjectured monophyly of the Panorpida is historically based on morphological evidence, namely the reduction or loss of the ovipositor and several internal characteristics, including a muscle connecting a pleuron and the first axillary sclerite at the base of the wing, various features of the larval maxilla and labium, and basal fusion of CuP and A1 veins in the hind wings. The monophyly of the Panorpida is also supported by recent molecular data.Planorboidea
Planorboidea is a superfamily of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks.All of the gastropods in this superfamily are sinistral in shell coiling.
The monophyly of Planorboidea was confirmed by Albrecht et al. (2007).Rhabditophora
Rhabditophora (from rhabdito-, rhabdite + Greek -φορος [-phoros], bearer, i.e., "rhabdite bearers") is a class of flatworms. It includes all parasitic flatworms (clade Neodermata) and most free-living species that were previously grouped in the now obsolete class Turbellaria. Therefore, it contains the majority of species in the phylum Platyhelminthes, excluding only the catenulids, to which they appear to be the sister group.
The clade Rhabditophora was originally erected by Ulrich Ehlers in 1985 based on morphological analyses and its monophyly was later confirmed by molecular studies.Scalidophora
Scalidophora is a group of marine pseudocoelomate protostomes that was proposed on morphological grounds to unite three phyla: the Kinorhyncha, the Priapulida and the Loricifera. The three phyla have four characters in common — chitinous cuticle that is moulted, rings of scalids on the introvert, flosculi, and two rings of introvert retracts. However, the monophyly of the Scalidophora is not supported by molecular studies, where the position of the Loricifera was uncertain or as sister to the Panarthropoda. Both studies supported a reduced Scalidophora comprising the Kinorhyncha and Priapulida as sister phyla. Their closest relatives are the Panarthropoda, Nematoda and Nematomorpha; thus they are placed in the group Ecdysozoa.
The two species in the genus Markuelia, known from fossilized embryos from the middle Cambrian, are thought to be stem Scalidophorans.
The group has also been considered a single group, Cephalorhyncha, with three classes.
The group is named after the spines (scalids) covering the introvert (head that can be retracted into the trunk).Sphaeropleales
Sphaeropleales is an order of green algae that used to be called Chlorococcales. The order includes some of the most common freshwater planktonic algae such as Scenedesmus and Pediastrum. The Spaeropleales includes vegetatively non-motile unicellular or colonial taxa that have biflagellate zoospores with flagella that are directly opposed in direction (the DO arrangement): Sphaeroplea, Atractomorpha, Neochloris, Hydrodictyon, and Pediastrum. All of these taxa have basal body core connections.With an increase in the number of taxa for which sequence data are available, there is evidence of an expanded DO clade that includes additional zoosporic (Bracteacoccus, Schroederia) and some strictly autosporic genera such as Ankistrodesmus, Scenedesmus, Selenastrum, and Monoraphidium. The filamentous Microspora has been allied with the coccoid genus Bracteacoccus based on molecular data.
Monophyly of the DO clade is supported by phylogenetic analysis of multi-gene data.Tritonioidea
Tritonioidea is a superfamily of small sea slugs, nudibranchs, shell-less marine gastropod mollusks in the clade Dendronotida.Tritonioidea is the only superfamily in the clade Dendronotida.
The taxonomy of Bouchet & Rocroi for the clade Dendronotida was largely based on the classification established by Boss in 1982, who in turn based his conclusions on the study by Odhner in 1968.The study of Wägele and Willan, published in 2000, concluded that Dendronotida is monophyletic, although this monophyly had been questioned, based on the wide variety in sperm morphology, in a paper by Healy & Willan in 1991.