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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Angiosperm Phylogeny Group | 1/3 | https://en.wikipedia.org/wiki/Angiosperm_Phylogeny_Group | reference | science, encyclopedia | 2026-05-05T10:21:13.405150+00:00 | kb-cron |
The Angiosperm Phylogeny Group (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 discovered through phylogenetic studies. As of 2016, four incremental versions of a classification system have resulted from this collaboration, published in 1998, 2003, 2009 and 2016. An important motivation for the group was what they considered deficiencies in prior angiosperm classifications since they were not based on monophyletic groups (i.e., groups that include all the descendants of a common ancestor). APG publications are increasingly influential, with a number of major herbaria changing the arrangement of their collections to match the latest APG system.
== Angiosperm classification and the APG ==
In the past, classification systems were typically produced by an individual botanist or by a small group. The result was a large number of systems (see List of systems of plant taxonomy). Different systems and their updates were generally favoured in different countries. Examples are the Engler system in continental Europe, the Bentham & Hooker system in Britain (particularly influential because it was used by Kew), the Takhtajan system in the former Soviet Union and countries within its sphere of influence and the Cronquist system in the United States. Before the availability of genetic evidence, the classification of angiosperms (also known as flowering plants, Angiospermae, Anthophyta or Magnoliophyta) was based on their morphology (particularly of their flower) and biochemistry (the kinds of chemical compounds in the plant). After the 1980s, detailed genetic evidence analysed by phylogenetic methods became available and while confirming or clarifying some relationships in existing classification systems, it radically changed others. This genetic evidence created a rapid increase in knowledge that led to many proposed changes; stability was "rudely shattered". This posed problems for all users of classification systems (including encyclopaedists). The impetus came from a major molecular study published in 1993 based on 5000 flowering plants and a photosynthesis gene (rbcL). This produced a number of surprising results in terms of the relationships between groupings of plants, for instance the dicotyledons were not supported as a distinct group. At first there was a reluctance to develop a new system based entirely on a single gene. However, subsequent work continued to support these findings. These research studies involved an unprecedented collaboration between a very large number of scientists. Therefore, rather than naming all the individual contributors a decision was made to adopt the name Angiosperm Phylogeny Group classification, or APG for short. The first publication under this name was in 1998, and attracted considerable media attention. The intention was to provide a widely accepted and more stable point of reference for angiosperm classification. As of 2016, three revisions have been published, in 2003 (APG II), in 2009 (APG III) and in 2016 (APG IV), each superseding the previous system. Thirteen researchers have been listed as authors to the three papers, and a further 43 as contributors (see Members of the APG below). A classification presents a view at a particular point in time, based on a particular state of research. Independent researchers, including members of the APG, continue to publish their own views on areas of angiosperm taxonomy. Classifications change, however inconvenient this is to users. However, the APG publications are increasingly regarded as an authoritative point of reference and the following are some examples of the influence of the APG system:
A significant number of major herbaria, including Kew, are changing the order of their collections in accordance with APG. The influential World Checklist of Selected Plant Families (also from Kew) is being updated to the APG III system. In the United States in 2006, a photographic survey of the plants of the US and Canada is organized according to the APG II system. In the UK, the 2010 edition of the standard flora of the British Isles (by Stace) is based on the APG III system. The previous editions were based on the Cronquist system.
== Principles of the APG system == The principles of the APG's approach to classification were set out in the first paper of 1998, and have remained unchanged in subsequent revisions. Briefly, these are:
The Linnean system of orders and families should be retained. "The family is central in flowering plant systematics." An ordinal classification of families is proposed as a "reference tool of broad utility". Orders are considered to be of particular value in teaching and in studying family relationships. Groups should be monophyletic (i.e. consist of all descendants of a common ancestor). The main reason why existing systems are rejected is because they do not have this property, they are not phylogenetic. A broad approach is taken to defining the limits of groups such as orders and families. Thus of orders, it is said that a limited number of larger orders will be more useful. Families containing only a single genus and orders containing only a single family are avoided where this is possible without violating the over-riding requirement for monophyly. Above or parallel to the level of orders and families, the term clades is used more freely. (Some clades have later been given formal names in a paper associated with the 2009 revision of the APG system.) The authors say that it is "not possible, nor is it desirable" to name all clades in a phylogenetic tree; however, systematists need to agree on names for some clades, particularly orders and families, to facilitate communication and discussion. For a detailed discussion on phylogenetic nomenclature, see Cantino et al. (2007).)
== APG I (1998) ==