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Angiosperm Phylogeny Group
The Angiosperm Phylogeny Group is an international group of systematic botanists who have come together to try to establish a consensus view of the taxonomy of flowering plants in the light of the rapid rise of molecular systematics.
The angiosperms or flowering plants, now technically referred to as Magnoliophyta, are one of the groups of organisms whose classification has been affected most radically as direct molecular analysis of relationships has become available. The influential classification scheme published by Arthur Cronquist in 1981, the Cronquist system, was already being superseded during the 1990s by improved schemes produced by W. S. Judd and others. However all of these schemes depended on the analysis of plant morphology, various aspects of the visible structures of plants. Direct analysis of the molecular content of the genetic material has made possible a much closer approach to the cladistic goal of making classification reflect descent. The molecular data that have become available, since around 1990, have clarified our views of some relationship and radically changed others.
The rapid increase in knowledge has led to many proposed changes in classifications, and these pose problems both for systematists and for users of classifications (such as encyclopaedists). By bringing together researchers from major institutions world-wide, and publishing jointly, the Angiosperm Phylogeny Group have sought to provide some stable points of reference, while making clear where our knowledge is too limited, or too much in flux, to allow a firm classification at this time.
The first APG classification was published in 1998; a revised version was published in 2003 (APG, 2003), and is known as APG II 2003 or just APG II. Its major innovations were:
- to place a substantial number of taxa whose classification had been left undetermined in the original version
- to offer alternative classifications for some groups, in which for example a number of families can either be regarded as separate or can be merged into a single larger family. APG II refers so such groups as "bracketed" taxa.
Bracketed taxa are introduced to help cope with the transition from the older, morphologically based classifications to the newer, molecularly-based systems, since the process has tended to produce a number of rather small taxa, e.g. monogeneric families, which are inconvenient for users. As the APG authors note (p. 402), "We generally accept the opinion of specialists... but we also recognise that specialists nearly always favour splitting of groups...".
Independent researchers, including members of the APG, continue to publish their own views on areas of angiosperm taxonomy, and in any case no classification is ever final; it represents a consensus (often a compromise) view at a particular point in time, based on a particular state of research, and new results are always appearing. Nonetheless the APG publications are increasingly regarded as an authoritative point of reference, and many botanists (including Wikipedia contributors) rely on them as a source for taxonomic assessments that are readily accessible and whose basis can be understood by all.
Institutions represented among the principal authors of the APG II classification include:
- Royal Swedish Academy of Sciences
- Uppsala University, Sweden
- Royal Botanic Gardens, Kew, United Kingdom
- University of Maryland, College Park, USA
- University of Florida, Gainsville, USA
- Missouri Botanical Garden, USA
with contributions from many other institutions world-wide.
- Angiosperm Phylogeny Group (2003). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141: 399-436. (Available online: Abstract | Full text (HTML) | Full text (PDF))
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