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.
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 main groups in the system (all unranked clades) are: The APG system recognises 462 families and 40 orders: these are assigned as follows.