Linnaean taxonomy

Source: Wikipedia, the free encyclopedia.
The title page of Systema Naturae, Leiden (1735)

Linnaean taxonomy can mean either of two related concepts:

  1. The particular form of biological classification (taxonomy) set up by Carl Linnaeus, as set forth in his Systema Naturae (1735) and subsequent works. In the taxonomy of Linnaeus there are three kingdoms, divided into classes, and they, in turn, into lower ranks in a hierarchical order.
  2. A term for rank-based classification of organisms, in general. That is, taxonomy in the traditional sense of the word: rank-based
    scientific classification. This term is especially used as opposed to cladistic systematics, which groups organisms into clades. It is attributed to Linnaeus, although he neither invented the concept of ranked classification (it goes back to Plato and Aristotle
    ) nor gave it its present form. In fact, it does not have an exact present form, as "Linnaean taxonomy" as such does not really exist: it is a collective (abstracting) term for what actually are several separate fields, which use similar approaches.

Linnaean name also has two meanings, depending on the context: it may either refer to a formal name given by Linnaeus (personally), such as

Giraffa camelopardalis Linnaeus, 1758; or a formal name in the accepted nomenclature (as opposed to a modernistic clade
name).

The taxonomy of Linnaeus

In his Imperium Naturae,

biological nomenclature, now regulated by the nomenclature codes. Two of his works, the first edition of the Species Plantarum (1753) for plants and the tenth edition of the Systema Naturae (1758), are accepted as part of the starting points of nomenclature; his binomials (names for species) and generic names take priority over those of others.[1]
However, the impact he had on science was not because of the value of his taxonomy.

Linnaeus' kingdoms were in turn divided into

genera (singular: genus), and species (singular: species), with an additional rank lower than species, though these do not precisely correspond to the use of these terms in modern taxonomy.[2]

Classification of plants

In Systema Naturae (1735), his classes and orders of plants, according to his Systema Sexuale, were not intended to represent natural groups (as opposed to his ordines naturales in his Philosophia Botanica) but only for use in identification. However, in 1737 he published Genera Plantarum in which he claimed that his classification of genera was a natural system.[3] His botanical classification and sexual system were used well into the nineteenth century.[4] Within each class were several orders. This system is based on the number and arrangement of male (stamens) and female (pistils) organs.[5]

Key to the Sexual System (from the 10th, 1758, edition of the Systema Naturae)
pistil

The Linnaean classes for plants, in the Sexual System, were (page numbers refer to Species plantarum):

  • Classis 1. Monandria: flowers with 1 stamen
  • Classis 2. Diandria: flowers with 2 stamens
  • Classis 3. Triandria: flowers with 3 stamens
  • Classis 4. Tetrandria: flowers with 4 stamens
  • Classis 5. Pentandria: flowers with 5 stamens
  • Classis 6. Hexandria: flowers with 6 stamens
    • Hexandria monogynia pp. 285–352[6]
    • Hexandria polygynia pp. 342–343[7]
  • Classis 7. Heptandria: flowers with 7 stamens
  • Classis 8. Octandria: flowers with 8 stamens
  • Classis 9. Enneandria: flowers with 9 stamens
  • Classis 10. Decandria: flowers with 10 stamens
  • Classis 11. Dodecandria: flowers with 11 to 19 stamens
  • Classis 12. Icosandria: flowers with 20 (or more) stamens,
    perigynous
  • Classis 13. Polyandria: flowers with many stamens, inserted on the receptacle
  • Classis 14. Didynamia: flowers with 4 stamens, 2 long and 2 short
    • Gymnospermia[8]
    • Angiospermia[9]
  • Classis 15. Tetradynamia: flowers with 6 stamens, 4 long and 2 short[10]
  • Classis 16. Monadelphia; flowers with the anthers separate, but the filaments united, at least at the base
  • Classis 17. Diadelphia; flowers with the stamens united in two separate groups[14]
  • Classis 18. Polyadelphia; flowers with the stamens united in several separate groups[18]
  • Classis 19. Syngenesia; flowers with stamens united by their anthers[22]
    • Polygamia aequalis[23]
    • Polygamia superba[24]
    • Polygamia frustranea[25]
    • Polygamia necessaria[26]
    • Monogamia[27]
  • Classis 20. Gynandria; flowers with the stamens united to the pistils[28]
  • Classis 21. Monoecia:
    monoecious
    plants
  • Classis 22. Dioecia:
    dioecious
    plants
  • Classis 23. Polygamia:
    polygamodioecious
    plants
  • Classis 24. Cryptogamia: the "flowerless" plants, including ferns, fungi, algae, and bryophytes

The classes based on the number of stamens were then subdivided by the number of pistils, e.g. Hexandria monogynia with six stamens and one pistil.[29] Index to genera p. 1201[30]

By contrast his ordines naturales numbered 69, from Piperitae to Vagae.

Classification for animals

The 1735 classification of animals

Only in the Animal Kingdom is the higher taxonomy of Linnaeus still more or less recognizable and some of these names are still in use, but usually not quite for the same groups. He divided the Animal Kingdom into six classes. In the tenth edition, of 1758, these were:

Classification for minerals

His taxonomy of minerals has long since been dropped from use. In the tenth edition, 1758, of the Systema Naturae, the Linnaean classes were:

  • Classis 1. Petræ
  • Classis 2. Mineræ
  • Classis 3. Fossilia
  • Classis 4. Vitamentra

Rank-based scientific classification

This rank-based method of classifying living organisms was originally popularized by (and much later named for) Linnaeus, although it has changed considerably since his time. The greatest innovation of Linnaeus, and still the most important aspect of this system, is the general use of

binomen
(the technical term for a binomial in the case of animals). Prior to Linnaean taxonomy, animals were classified according to their mode of movement.

Linnaeus's use of binomial nomenclature was anticipated by the theory of definition used in Scholasticism. Scholastic logicians and philosophers of nature defined the species human, for example, as Animal rationalis, where animal was considered a genus and rationalis (Latin for "rational") the characteristic distinguishing humans from all other animals. Treating animal as the immediate genus of the species human, horse, etc. is of little practical use to the biological taxonomist, however. Accordingly, Linnaeus's classification treats animal as a class including many genera (subordinated to the animal "kingdom" via intermediary classes such as "orders"), and treats homo as the genus of a species Homo sapiens, with sapiens (Latin for "knowing" or "understanding") playing a differentiating role analogous to that played, in the Scholastic system, by rationalis (the word homo, Latin for "human being", was used by the Scholastics to denote a species, not a genus).

A strength of Linnaean taxonomy is that it can be used to organize the different kinds of living

nomenclature codes
.

Species can be placed in a

morph
); in botany, variety (varietas) and form (forma), etc.

Groups of organisms at any of these ranks are called taxa (singular: taxon) or taxonomic groups.

The Linnaean system has proven robust and it remains the only extant working classification system at present that enjoys universal scientific acceptance. However, although the number of ranks is unlimited, in practice any classification becomes more cumbersome the more ranks are added. Among the later subdivisions that have arisen are such entities as phyla, families, and tribes, as well as any number of ranks with prefixes (superfamilies, subfamilies, etc.). The use of newer taxonomic tools such as cladistics and phylogenetic nomenclature has led to a different way of looking at evolution (expressed in many nested clades) and this sometimes leads to a desire for more ranks. An example of such complexity is the scheme for mammals proposed by McKenna and Bell.

Alternatives

Over time, understanding of the relationships between living things has changed. Linnaeus could only base his scheme on the structural similarities of the different organisms. The greatest change was the widespread acceptance of

extant and extinct
are linked together to construct a phylogeny. This is largely what is meant by the term 'Linnaean taxonomy' when used in a modern context. In
phylogeny). Such taxa may be either monophyletic (including all descendants) such as genus Homo, or paraphyletic (excluding some descendants), such as genus Australopithecus
.

Originally, Linnaeus established three kingdoms in his scheme, namely for

Bacteria and Archaea, which contain the prokaryotes, and Eukaryota, comprising the remaining forms. These arrangements should not be seen as definitive. They are based on the genomes of the organisms; as knowledge on this increases, classifications will change.[31]

Representing presumptive evolutionary relationships within the framework of Linnaean taxonomy is sometimes seen as problematic, especially given the wide acceptance of

molecular phylogenies that have challenged long-accepted classifications. Therefore, some systematists have proposed a PhyloCode
to replace it.

See also

References

Bibliography

External links