APG III system

The APG III system of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy being developed by the Angiosperm Phylogeny Group (APG). Published in 2009, it was superseded in 2016 by a further revision, the APG IV system.

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.

The APG III system recognized all of the 45 orders of the previous system, as well as 14 new ones. The order Ceratophyllales was erroneously marked as a new order, but it had been recognized in both of the previous APG systems. The newly recognized orders were:

The designation of alternative "bracketed families" was abandoned in APG III, because its inclusion in the previous system had been unpopular. APG III recognized 413 families, 43 fewer than in the previous system. Forty-four of the 55 "bracketed families" were discontinued, and 20 other families were discontinued as well.

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