32-399: Mesangiospermae is a clade of flowering plants (angiosperms) that contains about 99.95% of all angiosperm species. Mesangiosperms are therefore known as the core angiosperms , in contrast to the earlier-diverging species known as the basal angiosperms. Mesangiospermae includes about 350,000 species, while there are about 175 extant species of basal angiosperms. It is a name created under
64-766: A common ancestor and all its lineal descendants – on a phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are the fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over
96-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it
128-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking
160-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on
192-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,
224-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,
256-471: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution
288-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed
320-471: Is sometimes written as /Mesangiospermae even though this is not required by the PhyloCode . The "clademark" slash indicates that the term is intended as phylogenetically defined. In molecular phylogenetic studies , the mesangiosperms are always strongly supported as a monophyletic group. There is no distinguishing characteristic which is found in all mature mesangiosperms but which is not found in any of
352-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with
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#1733092561248384-717: The Hauterivian stage of the Cretaceous period . Molecular clock comparisons of DNA sequences indicate that the mesangiosperms originated between 140 and 150 Mya (million years ago) near the beginning of the Cretaceous period. This was about 25 Ma (million years) after the origin of the angiosperms in the mid- Jurassic . By 135Mya, the mesangiosperms had radiated into 5 groups: Chloranthales , Magnoliids , Monocots , Ceratophyllales , and Eudicots . The radiation into 5 groups probably occurred in about 4 million years. Because
416-409: The magnoliids —and Ginkgo biloba , which is not an angiosperm. The close relationships among flowering plants with tricolpate pollen grains was initially seen in morphological studies of shared derived characters . These plants have a distinct trait in their pollen grains of exhibiting three colpi or grooves paralleling the polar axis. Later molecular evidence confirmed the genetic basis for
448-400: The " Eudicot " monophyletic group, the "true dicotyledons " (which are distinguished from all other flowering plants by their tricolpate pollen structure). The number of pollen grain furrows or pores helps classify the flowering plants , with eudicots having three colpi ( tricolpate ), and other groups having one sulcus . Pollen apertures are any modification of the wall of
480-409: The basal angiosperms. Nevertheless, the mesangiosperms are recognizable in the earliest stage of embryonic development. The ovule contains a megagametophyte , also known as an embryo sac , that is bipolar in structure and contains 8 cell nuclei . The antipodal cells are persistent , and the endosperm is triploid . The oldest known fossils of flowering plants are fossil mesangiosperms from
512-410: The basal eudicots and the core eudicots . Basal eudicot is an informal name for a paraphyletic group. The core eudicots are a monophyletic group. A 2010 study suggested the core eudicots can be divided into two clades, Gunnerales and a clade called Pentapetalae , comprising all the remaining core eudicots. The Pentapetalae can be then divided into three clades: This division of the eudicots
544-429: The eudicots is tricolpates , a name which refers to the grooved structure of the pollen . Members of the group have tricolpate pollen, or forms derived from it. These pollens have three or more pores set in furrows called colpi. In contrast, most of the other seed plants (that is the gymnosperms , the monocots and the paleodicots) produce monosulcate pollen, with a single pore set in a differently oriented groove called
576-496: The evolutionary relationships among flowering plants with tricolpate pollen grains and dicotyledonous traits. The term means "true dicotyledons", as it contains the majority of plants that have been considered dicots and have characteristics of the dicots. One of the genetic traits which defines the eudicots is the duplication of DELLA protein-encoding genes in their most recent common ancestor . The term "eudicots" has subsequently been widely adopted in botany to refer to one of
608-553: The following clades: Amborellales Nymphaeales Austrobaileyales magnoliids Chloranthales monocots Ceratophyllales eudicots The mesangiosperms are usually recognized in classification systems that do not assign groups to taxonomic rank . The name Mesangiospermae is a branch-modified node-based name in phylogenetic nomenclature . It is defined as the most inclusive crown clade containing Platanus occidentalis , but not Amborella trichopoda , Nymphaea odorata , or Austrobaileya scandens . It
640-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"
672-469: The interval of this radiation (about 4 million years) is short in proportion to its age (about 145 million years), it had long appeared that the 5 groups of mesangiosperms had arisen simultaneously. The mesangiosperms were shown as an unresolved pentatomy in phylogenetic trees . In 2007, two studies attempted to resolve the phylogenetic relationships among these 5 groups by comparing large portions of their chloroplast genomes . These studies agreed on
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#1733092561248704-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"
736-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of
768-420: The most likely phylogeny for the mesangiosperms. In this phylogeny, the monocots are sister to the clade [Ceratophyllales + eudicots]. However, this result is not strongly supported. The approximately unbiased topology test showed that some of the other possible positions of the monocots had more than 5% probability of being correct. The major weakness of these 2 studies was the small number of species whose DNA
800-440: The most well-known eudicot genera are those of the sunflower ( Helianthus ), dandelion ( Taraxacum ), forget-me-not ( Myosotis ), cabbage ( Brassica ), apple ( Malus ), buttercup ( Ranunculus ), maple ( Acer ) and macadamia ( Macadamia ). Most leafy, mid-latitude trees are also classified as eudicots, with notable exceptions being the magnolias and American tulip tree ( Liriodendron )—which belong to
832-428: The pollen grain. These modifications include thinning, ridges and pores, they serve as an exit for the pollen contents and allow shrinking and swelling of the grain caused by changes in moisture content. The elongated apertures/ furrows in the pollen grain are called colpi (singular colpus ), which, along with pores, are a chief criterion for identifying the pollen classes. The eudicots can be divided into two groups:
864-630: The rules of the PhyloCode system of phylogenetic nomenclature . While such a clade with a similar circumscription exists in the APG III system , it was not given a name. Besides the mesangiosperms, the other groups of flowering plants are Amborellales , Nymphaeales , and Austrobaileyales . These constitute a paraphyletic grade called basal angiosperms . The order names , ending in -ales are used here without reference to taxonomic rank because these groups contain only one order. Mesangiospermae includes
896-709: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Eudicots The eudicots , Eudicotidae , or eudicotyledons are a clade of flowering plants (angiosperms) which are mainly characterized by having two seed leaves (cotyledons) upon germination . The term derives from dicotyledon (etymologically, eu = true; di = two; cotyledon = seed leaf). Historically, authors have used
928-454: The sulcus. The name "tricolpates" is preferred by some botanists to avoid confusion with the dicots, a nonmonophyletic group. The name "eudicots" (plural) is used in the APG systems (from APG system , of 1998, to APG IV system , of 2016) for classification of angiosperms. It is applied to a clade , a monophyletic group, which includes most of the (former) dicots. "Tricolpate" is a synonym for
960-442: The terms tricolpates or non-magnoliid dicots . The current botanical terms were introduced in 1991, by evolutionary botanist James A. Doyle and paleobotanist Carol L. Hotton, to emphasize the later evolutionary divergence of tricolpate dicots from earlier, less specialized, dicots. Scores of familiar plants are eudicots, including many commonly cultivated and edible plants, numerous trees , tropicals and ornamentals. Among
992-539: The two largest clades of angiosperms (constituting over 70% of the angiosperm species), monocots being the other. The remaining angiosperms include magnoliids and what are sometimes referred to as basal angiosperms or paleodicots, but these terms have not been widely or consistently adopted, as they do not refer to a monophyletic group. According to molecular clock calculations, the lineage that led to eudicots split from other plants about 134 million years ago or 155-160 million years ago. The earlier name for
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1024-446: Was being used in the phylogenetic analysis, 45 in one study and 64 in the other. This was unavoidable, because complete chloroplast genome sequences are known for only a few plants. Clade In biological phylogenetics , a clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of
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