The APG system (Angiosperm Phylogeny Group system) of plant classification is the first version of a modern, mostly
molecular
A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings.
A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished ...
-based,
system of plant taxonomy. Published in 1998 by the
Angiosperm Phylogeny Group
The Angiosperm Phylogeny Group, or APG, is an informal international group of systematic botanists who collaborate to establish a consensus on the taxonomy of flowering plants (angiosperms) that reflects new knowledge about plant relationships dis ...
, it was replaced by the improved
APG II#REDIRECT APG II system {{R from other capitalisation ...
in 2003,
APG III system
The APG III system of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy being developed by the Angiosperm Phylogeny Group (APG). Published in 2009, it was superseded in 2016 by a furth ...
in 2009 and
APG IV systemAPG is an abbreviation with several different meanings:
* Aberdeen Proving Ground, a United States Army installation in Aberdeen, Maryland, also
**Phillips Army Airfield, the airfield of the above, from its IATA airport code
* Aboriginal Provisional ...
in 2016.
History
The original APG system is unusual in being based, not on total evidence, but on the
cladistic
Cladistics (, from Greek , ''kládos'', "branch") is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships ...
analysis of the DNA sequences of three genes, two chloroplast genes and one gene coding for ribosomes. Although based on
molecular evidence only, its constituent groups prove to be supported by other evidence as well, for example
pollen
Pollen Tube Diagram
Pollen is a powdery substance consisting of pollen grains which are male microgametophytes of seed plants, which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gamet ...
morphology
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
*Morphology (archaeology), study of the shapes or forms of artifacts
*Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
supports the split between the
eudicots
The eudicots, Eudicotidae or eudicotyledons are a clade of flowering plants mainly characterized by having two seed leaves upon germination. The term derives from Dicotyledons.
Traditionally they were called tricolpates or non-magnoliid dicots b ...
and the rest of the former
dicotyledons
200px, Young castor oil plant showing its prominent two embryonic leaves (cotyledons), that differ from the adult leaves.
The dicotyledons, also known as dicots (or more rarely dicotyls), are one of the two groups into which all the flowering ...
.
The system is rather controversial in its decisions at the family level, splitting a number of long-established families and submerging some other families. It also is unusual in not using
botanical name
A botanical name is a formal scientific name conforming to the ''International Code of Nomenclature for algae, fungi, and plants'' (ICN) and, if it concerns a plant cultigen, the additional cultivar or Group epithets must conform to the ''Internati ...
s above the level of order, that is, an order is the highest
rank
Rank is the relative position, value, worth, complexity, power, importance, authority, level, etc. of a person or object within a ranking, such as:
Level or position in a hierarchical organization
* Academic rank
* Diplomatic rank
* Hierarchy
* Hi ...
that will have a formal
botanical name
A botanical name is a formal scientific name conforming to the ''International Code of Nomenclature for algae, fungi, and plants'' (ICN) and, if it concerns a plant cultigen, the additional cultivar or Group epithets must conform to the ''Internati ...
in this system. Higher groups are defined only as
clades
A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic—that is, composed of a common ancestor and all its lineal descendants - on a phylogenetic tree. R ...
, with names such as
monocots
Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of th ...
,
eudicots
The eudicots, Eudicotidae or eudicotyledons are a clade of flowering plants mainly characterized by having two seed leaves upon germination. The term derives from Dicotyledons.
Traditionally they were called tricolpates or non-magnoliid dicots b ...
,
rosids
The rosids are members of a large clade (monophyletic group) of flowering plants, containing about 70,000 species, more than a quarter of all angiosperms.
The clade is divided into 16 to 20 orders, depending upon circumscription and classification ...
,
asterids
Oregano from Lamiales
In the APG IV system (2016) for the classification of flowering plants, the name asterids denotes a clade (a monophyletic group). Common examples include the common daisy, the forget-me-nots, nightshades (including potatoes, ...
.
The APG system was superseded in 2003 by a revision, the
APG II system#REDIRECT APG II system#REDIRECT APG II system {{R from other capitalisation ... {{R from other capitalisation ...