TheAPG system (Angiosperm Phylogeny Group system) of plant classification is the first version of a modern, mostlymolecular-based,system of plant taxonomy. Published in 1998 by theAngiosperm Phylogeny Group, it was replaced by the improvedAPG II in 2003,APG III system in 2009 andAPG IV system in 2016.
The original APG system is unusual in being based, not on total evidence, but on thecladistic analysis of the DNA sequences of three genes, two chloroplast genes and one gene coding for ribosomes. Although based onmolecular evidence only, its constituent groups prove to be supported by other evidence as well, for examplepollenmorphology supports the split between theeudicots and the rest of the formerdicotyledons.
The system is rather controversial in its decisions at the family level, splitting a number of long-established families and submerging some other families. It also is unusual in not usingbotanical names above the level of order, that is, an order is the highestrank that will have a formalbotanical name in this system. Higher groups are defined only asclades, with names such asmonocots,eudicots,rosids,asterids.
The APG system was superseded in 2003 by a revision, theAPG II system, in 2009 by a next revision, theAPG III system, and then in 2016 by a further revision, theAPG IV system.
The main groups in the system (allunrankedclades) are:
The APG system recognises 462 families and 40 orders: these are assigned as follows. In the beginning of each listing some families or orders that are not placed in a further clade:
Note: "+ ..." = optional seggregrate family, that may be split off from the preceding family.
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