Angiosperm Phylogeny Group: Encyclopedia - Angiosperm Phylogeny Group

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, variously known as Angiospermae, Anthophyta, Magnoliophyta etc, 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 increasingly challenged during the 1990s. These classification schemes were based on molecular as well as morphological relationships, unlike older classifications that were based almost entirely on morphology. 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 a stable point of reference, publishing the APG-system (1998). This system is based on two chloroplast genes and one gene coding for ribosomes. This system deals mostly with higher ranks and, as there are still severe limits to our knowledge, a firm classification is not possible in all cases.

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:

• not to use formal, scientific names above the level of order
• to place a substantial number of taxa whose classification has traditionally been uncertain
• 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 to 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 presents a view at a particular point in time, based on a particular state of research. New results are always appearing. Nonetheless the APG publications are increasingly regarded as an authoritative point of reference.

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.

Adapted from the Wikipedia article "Angiosperm Phylogeny Group", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki