The original APG system is unusual in being based, not on total evidence, but on the
cladistic analysis of the DNA sequences of three genes, two chloroplast genes and one gene coding for ribosomes. Although based on
molecular evidence only, its constituent groups prove to be supported by other evidence as well, for example
pollen morphology supports the split between the
eudicots and the rest of the former
dicotyledons. 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 using
botanical names above the level of order, that is, an order is the highest
rank that will have a formal
botanical name in this system. Higher groups are defined only as
clades, with names such as
monocots,
eudicots,
rosids,
asterids. The APG system was superseded in 2003 by a revision, the
APG II system, in 2009 by a next revision, the
APG III system, and then in 2016 by a further revision, the
APG IV system. ==Groups==