APG III system

The APG III system (Angiosperm Phylogeny Group III system) of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy. The system was published in 2009 by the Angiosperm Phylogeny Group, 6½ years after its predecessor the APG II system was published, and 11 years after the initial APG system was published in 1998.

Along with the publication outlining the new system, there were two accompanying publications in the same issue of the Botanical Journal of the Linnean Society. The first, by Chase & Reveal, was a formal phylogenetic classification of all land plants (embryophytes), compatible with the APG III classification. As the APG have chosen to eschew ranks above order, this paper was meant to fit the system into the existing Linnaean hierarchy for those that prefer such a classification. The result was that all land plants were placed in the class Equisitopsida, which was then divided into 16 subclasses (including the Magnoliidae, containing all flowering plants) and a multitude of superorders. The second, by Haston et al., was a linear sequence of families following the APG III system (LAPG III). This provided a numbered list to the 413 families of APG III. A linear sequence is of particular use to herbarium curators and those working on floristic works wishing to arrange their taxa according to APG III.