Division (taxonomy)

This article is about categorisations of organisms. For division of invidual cells, see cell division.

Division is a taxonomic rank in biological classification that is used differently in zoology and in botany.

In botany and mycology, division is the traditional name for a rank now considered equivalent to phylum. The use of either term is allowed under the International Code of Botanical Nomenclature.^[1]

The main Divisions of land plants are the Marchantiophyta (liverworts), Anthocerotophyta (hornworts), Bryophyta (mosses), Filicophyta (ferns), Sphenophyta (horsetails), Cycadophyta (cycads), Ginkgophyta (ginkgo)s, Pinophyta (conifers), Gnetophyta (gnetophytes), and the Magnoliophyta (Angiosperms, flowering plants). The Magnoliophyta now dominate terrestrial ecosystems, comprising 80% of vascular plant species.^[2]

In zoology, the term division is applied to an optional rank subordinate to the infraclass and superordinate to the legion and cohort. A widely used classification (e.g. Carroll 1988^[3]) recognises teleost fishes as a Division Teleostei within Class Actinopterygii (the ray-finned fishes). Less commonly (as in Milner 1988^[4]), living tetrapods are ranked as Divisions Amphibia and Amniota within the clade of vertebrates with fleshy limbs (Sarcopterygii).

Proposals for standardisation

In 1978, a group of botanists including Harold Charles Bold, Arthur Cronquist and Lynn Margulis proposed replacing the term "division" with "phylum" in botanical nomenclature, arguing that maintaining different terms for the same taxonomic rank across biological kingdoms created unnecessary confusion. This was particularly problematic for unicellular eukaryotes, where heterotrophic organisms were classified under zoological nomenclature (using "phylum") while autotrophic organisms fell under botanical nomenclature (using "division"). They proposed updating the International Code of Botanical Nomenclature to use "phylum" and "subphylum" throughout, while maintaining that names originally published as divisions would be treated as if they had been published as phyla.^[5]

Molecular phylogenetic classification

The use of molecular methods, particularly 16S ribosomal RNA analysis, helped establish major bacterial divisions in the 1980s. In 1985, Carl Woese and colleagues identified ten major groups of eubacteria through oligonucleotide signature analysis, noting that these groupings were "appropriately termed eubacterial Phyla or Divisions." This work provided early molecular evidence for the equivalence of bacterial divisions with phyla and helped establish a phylogenetic basis for high-level bacterial classification.^[6]

Viruses and prokaryotes

In 2020, the International Committee on Taxonomy of Viruses (ICTV) formalised a 15-rank hierarchical classification system, ranging from the highest rank "realm" (rather than domain) down through the lower ranks, notably using "phylum" rather than "division". Under this system, the first viral realm established was Riboviria, encompassing all RNA viruses that encode an RNA-directed RNA polymerase.^[7]

In 2021, the International Code of Nomenclature of Prokaryotes (ICNP) formally included the rank of phylum for the first time, adopting the suffix "-ota" for phylum names. This led to the publication of names for 46 prokaryotic phyla with cultured representatives, replacing some established names with neologisms – for example, "Proteobacteria" became "Pseudomonadota" and "Firmicutes" became "Bacillota".^[8]

References

1. McNeill, J.; et al., eds. (2012). International Code of Nomenclature for algae, fungi, and plants (Melbourne Code), Adopted by the Eighteenth International Botanical Congress Melbourne, Australia, July 2011 (electronic ed.). International Association for Plant Taxonomy. Retrieved 2017-05-14.
2. Judd, Walter S.; Campbell, Christopher S.; Kellogg, Elizabeth A.; Stevens, Peter F.; Donoghue, Michael J. (2002). Plant systematics, a phylogenetic approach (2nd ed.). Sunderland MA, USA: Sinauer Associates Inc. ISBN 0-87893-403-0.
3. (Carroll 1988)
4. (Milner 1988)
5. Bold, H.C.; Cronquist, A.; Jeffey, C.; Johnson, L.A.S.; Marguilis, L.; Merximiller, H.; Takhtajan, A.L. (1978). "Proposa (10) to substitute the term phylum for division for groups treated as plants" (PDF). Taxon. 27 (1): 121–122.
6. Woese, C.R.; Stackebrandt, E.; Macke, T.J.; Fox, G.E. (1985). "A phylogenetic definition of the major eubacterial taxa". Systematic and Applied Microbiology. 6 (2): 143–151. Bibcode:1985SyApM...6..143W. doi:10.1016/S0723-2020(85)80047-3. PMID 11542017.
7. International Committee on Taxonomy of Viruses Executive Committee; Gorbalenya, Alexander E.; Krupovic, Mart; Mushegian, Arcady; Kropinski, Andrew M.; Siddell, Stuart G.; Varsani, Arvind; Adams, Michael J.; Davison, Andrew J.; Dutilh, Bas E.; Harrach, Balázs; Harrison, Robert L.; Junglen, Sandra; King, Andrew M. Q.; Knowles, Nick J.; Lefkowitz, Elliot J.; Nibert, Max L.; Rubino, Luisa; Sabanadzovic, Sead; Sanfaçon, Hélène; Simmonds, Peter; Walker, Peter J.; Zerbini, F. Murilo; Kuhn, Jens H. (2020). "The new scope of virus taxonomy: partitioning the virosphere into 15 hierarchical ranks". Nature Microbiology. 5 (5): 668–674. doi:10.1038/s41564-020-0709-x. PMC 7186216. PMID 32341570.
8. Pallen, Mark J. (2024). "The dynamic history of prokaryotic phyla: discovery, diversity and division". International Journal of Systematic and Evolutionary Microbiology. 74 (9): e006508. doi:10.1099/ijsem.0.006508. PMC 11382960. PMID 39250184.

Works cited

• Carroll, Robert L. (1988), Vertebrate Paleontology and Evolution, New York: W.H. Freeman & Co., ISBN 0-716-7-1822-7
• Milner, Andrew (1988), "The relationships and origin of living amphibians", in M.J. Benton (ed.), 'The Phylogeny and Classification of the Tetrapods, vol. 1: Amphibians, Reptiles, Birds, Oxford: Clarendon Press, pp. 59–102