Angiosperm Phylogeny Group - Angiosperm Classification and The APG

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).

See also: Flowering plants:History of classification

After the 1980's, detailed genetic evidence analysed by phylogenetic methods became available and while confirmed or clarified 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).

In the late 1990s, an informal group of researchers from major institutions worldwide came together under the title of the 'Angiosperm Phylogeny Group' or APG. Their intention was to provide a widely accepted and more stable point of reference for angiosperm classification. Their first attempt at a new system was published in 1998 (the APG system). As of 2010, two revisions have been published, in 2003 (APG II) and in 2009 (APG III), each superseding the previous system. Eight researchers have been listed as authors to the three papers, and a further 33 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 USA, a recent photographic survey of the plants of the USA and Canada is organized according to the APG II system.
• In the UK, the latest edition of the standard flora of the British Isles (by Stace) is based on the APG III system. The previous edition was based on the Cronquist system.

Peter F. Stevens, one of the authors of all three of the APG papers, maintains a web site, APweb, hosted by the Missouri Botanical Garden, which has been regularly updated since 2001, and is a useful source for the latest research in angiosperm phylogeny which follows the APG approach.