
TheAPG IV system of flowering plant classification is the fourth version of a modern, mostlymolecular-based,system of plant taxonomy forflowering plants (angiosperms) being developed by theAngiosperm Phylogeny Group (APG). It was published in 2016, seven years after its predecessor theAPG III system was published in 2009, and 18 years after the firstAPG system was published in 1998.[1] In 2009, a linear arrangement of the system was published separately;[2] the APG IV paper includes such an arrangement, cross-referenced to the 2009 one.[1]
Compared to the APG III system, the APG IV system recognizes five new orders (Boraginales,Dilleniales,Icacinales,Metteniusales andVahliales), along with some new families, making a total of 64 angiosperm orders and 416 families.[1] In general, the authors describe their philosophy as "conservative", based on making changes from APG III only where "a well-supported need" has been demonstrated. This has sometimes resulted in placements that are not compatible with published studies, but where further research is needed before the classification can be changed.[3]
Key to symbols used:
Like the earlier APG systems, the APG IV revision is based on aphylogenetic tree for the angiosperms, as shown below.[4]