This presentation has taken as standard the "three domain - six kingdom" model of organism diversity, based on 16S ribosomal RNA sequence comparisons, of Carl Woese and co-workers. This divides cellular organisms into:
GJ Olsen and CR Woese (1993). FASEB Journal 7: 113-123.
However, Robert H Whittaker and Lyn Margulis have suggested that organisms should be divided into five kingdoms: that is,
This model includes some "plants" as protists, and makes no distinction between Archaea and Bacteria.
RH Whittaker and L Margulis (1978). BioSystems 10: 3-18
To complicate matters, James Lake and co-workers have lately proposed a radical re-structuring of the "universal" phylogenetic tree, to split Archaea into Halobacteria, Methanogens and Eocytes. This would mean there are three major groupings of prokaryotes (Eubacteria + Halobacteria, Methanogens and Eocytes), which could all constitute kingdoms on their own, given each is as unrelated to the others as any are to Eukarya.
JA Lake (1991). Trends in Biochemical Sciences 16: 46-50.
There is also a 2-empire / 8-kingdom scheme, with Archaeobacteria and Eubacteria as kingdoms in Empire Bacteria, and 6 kingdoms in Empire Eukaryota:
Cavalier-Smith T (1993). Microbiological Reviews 57: 953-994
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