Kingdom (biology) - Systems of Classification - Summary

Summary

The sequence from the two-kingdom system up to Cavalier-Smith's six-kingdom system can be summarized in the table below.

Linnaeus
1735
Haeckel
1866
Chatton
1925
Copeland
1938
Whittaker
1969
Woese et al.
1977
Woese et al.
1990
Cavalier-Smith
1993
Cavalier-Smith
1998
2 kingdoms 3 kingdoms 2 empires 4 kingdoms 5 kingdoms 6 kingdoms 3 domains 8 kingdoms 6 kingdoms
(not treated) Protista Prokaryota Monera Monera Eubacteria Bacteria Eubacteria Bacteria
Archaebacteria Archaea Archaebacteria
Eukaryota Protoctista Protista Protista Eukarya Archezoa Protozoa
Protozoa
Chromista Chromista
Vegetabilia Plantae Plantae Plantae Plantae Plantae Plantae
Fungi Fungi Fungi Fungi
Animalia Animalia Animalia Animalia Animalia Animalia Animalia

Note that the equivalences in this table are not perfect. For example, Haeckel placed the red algae (his Florideae, modern Florideophyceae) and blue-green algae (his Archephyta, modern Cyanobacteria) in his Plantae.

The kingdom-level classification of life is still widely employed as a useful way of grouping organisms, notwithstanding some problems with this approach:

  • Kingdoms such as Bacteria represent grades rather than clades, and so are rejected by phylogenetic classification systems.
  • The most recent research does not support the classification of the eukaryotes into any of the standard systems. As of April 2010, no set of kingdoms is sufficiently supported by research to attain widespread acceptance. In 2009, Andrew Roger and Alastair Simpson emphasized the need for diligence in analyzing new discoveries: "With the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution."

Read more about this topic:  Kingdom (biology), Systems of Classification

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