Mesangiospermae is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

that contains the majority of

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

s (angiosperms). Mesangiosperms are therefore known as the core angiosperms, in contrast to the three orders of earlier-diverging species known as the

basal angiosperms The basal angiosperms are the flowering plants which diverged from the lineage leading to most flowering plants. In particular, the most basal angiosperms were called the ANITA grade, which is made up of ''Amborella'' (a single species of shrub f ...

: Nymphaeales (including water lilies),

Austrobaileyales Austrobaileyales is an order of flowering plants consisting of about 100 species of woody plants growing as trees, shrubs and lianas. A well known example is '' Illicium verum'', commonly known as star anise. The order belongs to the group of b ...

(including

star anise ''Illicium verum'' (star anise or badian, Chinese star anise, star anise seed, star aniseed and star of anise) is a medium-sized evergreen tree native to South China and northeast Vietnam. Its star-shaped pericarps harvested just before ripen ...

), and

Amborellales ''Amborella'' is a monotypic genus of understory shrubs or small trees endemic to the main island, Grande Terre, of New Caledonia in the southwest Pacific Ocean. The genus is the only member of the family Amborellaceae and the order Amborella ...

. Mesangiospermae includes about 350,000 species,Alan J. Paton, Neil Brummitt, Rafaël Govaerts, Kehan Harman, Sally Hinchcliffe, Bob Allkin, & Eimear Nic Lughadha (2008). "Towards Target 1 of the Global Strategy for Plant Conservation: a working list of all known plant species - progress and prospects". ''Taxon'' 57(2):602-611. while there are about 175 extant species of basal angiosperms. Peter F. Stevens (2001 onwards). Angiosperm Phylogeny Website In: Missouri Botanical Garden Website. (see ''External links'' below). It is a name created under the rules of the ''

PhyloCode The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature. Its current version is specifically designed to regulate the naming of clades, leaving the ...

'' system of

phylogenetic nomenclature Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional method, by which taxon names are defined by a '' type'', which c ...

. While such a clade with a similar circumscription exists in the APG III system, it was not given a name.

Phylogeny

Besides the mesangiosperms, the other groups of flowering plants are

, Nymphaeales, and

. These constitute a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

grade called

. The order

names A name is a term used for identification by an external observer. They can identify a class or category of things, or a single thing, either uniquely, or within a given context. The entity identified by a name is called its referent. A person ...

, ending in -ales are used here without reference to taxonomic rank because these groups contain only one order. Mesangiospermae includes the following clades: * Ceratophyllales * Chloranthales *

eudicots The eudicots or eudicotyledons are flowering plants that have two seed leaves (cotyledons) upon germination. The term derives from ''dicotyledon'' (etymologically, ''eu'' = true; ''di'' = two; ''cotyledon'' = seed leaf). Historically, authors h ...

* magnoliidae * monocots

Name

The mesangiosperms are usually recognized in

classification Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...

systems that do not assign groups to

taxonomic rank In biology, taxonomic rank (which some authors prefer to call nomenclatural rank because ranking is part of nomenclature rather than taxonomy proper, according to some definitions of these terms) is the relative or absolute level of a group of or ...

. The name Mesangiospermae is a branch-modified node-based name in

. It is defined as the most inclusive crown clade containing ''

Platanus occidentalis ''Platanus occidentalis'', also known as American sycamore, American planetree, western plane, occidental plane, buttonwood, and water beech, is a species of ''Platanus'' native to the eastern and central United States, the mountains of northeast ...

'', but not '' Amborella trichopoda'', '' Nymphaea odorata'', or '' Austrobaileya scandens''.Philip D. Cantino, James A. Doyle, Sean W. Graham, Walter S. Judd, Richard G. Olmstead, Douglas E. Soltis, Pamela S. Soltis, and Michael J. Donoghue. 2007. Electronic Supplement: pages E1-E44. To: Cantino et alii. 2007. "Towards a phylogenetic nomenclature of ''Tracheophyta''". ''Taxon'' 56(3):822-846. (see ''External links'' below). It is sometimes written as /Mesangiospermae even though this is not required by the

. The "clademark" slash indicates that the term is intended as phylogenetically defined.

Description

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

studies, the mesangiosperms are always strongly supported as a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group. Douglas E. Soltis, Pamela S. Soltis, Peter K. Endress, and Mark W. Chase (2005). ''Phylogeny and Evolution of the Angiosperms''. Sinauer: Sunderland, MA There is no distinguishing characteristic which is found in all mature mesangiosperms but which is not found in any of the basal angiosperms. Nevertheless, the mesangiosperms are recognizable in the earliest stage of embryonic development.William E. Friedman and Kirsten C. Ryerson (2009). "Reconstructing the ancestral female gametophyte of angiosperms: Insights from Amborella and other ancient lineages of flowering plants". ''American Journal of Botany'' 96(1):129-143. The

ovule In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the sporangium, megasporangium), ...

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 The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid (meaning three chromosome sets per nucleus) in most species, which may be auxin-driven. It surrounds the Embryo#Pla ...

is triploid.

History

The oldest known

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s of flowering plants are fossil mesangiosperms from the

Hauterivian The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.6 ± 2 Ma and 125.77 (million years ago). The Hauterivian is preceded by the Valangi ...

stage of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period. Else Marie Friis, K. Raunsgaard Pedersen, and Peter R. Crane (2006). "Cretaceous angiosperm flowers: Innovation and evolution in plant reproduction". ''Palaeogeography, Palaeoclimatology, Palaeoecology''232(2-4):251–293.

Molecular clock The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleot ...

comparisons of DNA sequences indicate that the mesangiosperms originated between 140 and 150 Mya (million years ago) near the beginning of the Cretaceous period.T. Jonathan Davies, Timothy G. Barraclough, Mark W. Chase, Pamela S. Soltis, Douglas E. Soltis, and Vincent Savolainen (2004). "Darwin's abominable mystery: Insights from a supertree of the angiosperms". ''Proceedings of the National Academy of Sciences'' 101(7):1904-1909. This was about 25 Ma (million years) after the origin of the angiosperms in the mid-

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

.Michael J. Moore, Charles D. Bell, Pamela S. Soltis, and Douglas E. Soltis (2007). "Using plastid genome-scale data to resolve enigmatic relationships among basal angiosperms". ''Proceedings of the National Academy of Sciences'' 104(49):19363-19368. By 135Mya, the mesangiosperms had radiated into 5 groups: Chloranthales, Magnoliids, Monocots, Ceratophyllales, and

Eudicots The eudicots or eudicotyledons are flowering plants that have two seed leaves (cotyledons) upon germination. The term derives from ''dicotyledon'' (etymologically, ''eu'' = true; ''di'' = two; ''cotyledon'' = seed leaf). Historically, authors h ...

. The radiation into 5 groups probably occurred in about 4 million years. Because 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 tree A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In ...

s. In 2007, two studies attempted to resolve the

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

relationships among these 5 groups by comparing large portions of their

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

genomes.Robert K. Jansen, Zhengqiu Cai, Linda A. Raubeson, Henry Daniell, Claude W. dePamphilis, James Leebens-Mack, Kai F. Müller, Mary Guisinger-Bellian, Rosemarie C. Haberle, Anne K. Hansen, Timothy W. Chumley, Seung-Bum Lee, Rhiannon Peery, Joel R. McNeal, Jennifer V. Kuehl, and Jeffrey L. Boore (2007). "Analysis of 81 genes from 64 plastid genomes resolves relationships in angiosperms and identifies genome-scale evolutionary patterns" ''Proceedings of the National Academy of Sciences'' 104(49):19369-19374 These studies agreed on the most likely phylogeny for the mesangiosperms. In this phylogeny, the monocots are

sister A sister is a woman or a girl who shares parents or a parent with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a familial relationship, it is sometimes used endearingly to ref ...

to the clade eratophyllales + 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 was being used in the phylogenetic analysis, 45 in one study and 64 in the other. This was unavoidable, because complete chloroplast genome

sequences In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is call ...

are known for only a few plants.

References

Bibliography

* * *

External links

Angiosperm Phylogeny
a
Missouri Botanical Garden
*
Divergence Times
T. Jonathan Davies et alii. (2004). ''PNAS'' 101(7):1904-1909.

In
Montreal genomics
{{Taxonbar, from=Q2710933 Angiosperms Plant unranked clades