Introduction to Taxonomy

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Taxonomy is the classification of organisms in an ordered system that indicates natural relationships.

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Carolus Linnaeus was a Swedish botanist whom founded the taxonomic system used in Zoology. His system has evolved over time. The Linnaean system designates five such classifications: flora, fauna, fungi, prokaryotes, and protoctists. Depending on the person studying and reviewing the taxonomy of Phyla in Zoology, these trees may differ, especially with regards to ongoing research in many fields of study.

Title page of Systema Naturae, 1760.
  • Definitions:
    • Kingdom The highest taxonomic classification into which organisms are grouped.
    • Phylum A primary division of the animal kingdom ranking above a class
    • Class A primary taxonomic category of organisms ranking below a phylum and ranking above an order
    • Order A primary taxonomic category of organisms ranking below a class and above a family
    • Family A primary taxonomic category of organisms ranking below an order and above a genus
    • Genus A primary taxonomic category of organisms ranking below an order and above a genus. It is comprised of species displaying similar characteristics. In taxonomic nomenclature, the genus is used, either alone or followed by a Latin adjective or epithet, to form the species name.
    • Species A primary taxonomic category of organisms, ranking below a genus and comprised of related organisms capable of interbreeding. In writing, organisms in this category are represented in binomial nomenclature by an uncapitalized Latin adjective or noun following a capitalized genus name, as seen in Anolis carolinensis. The genus is often shorthanded, as found in A. carolinensis.
    • Trinomial nomenclature A three-part taxonomic designation indicating genus, species, and subspecies, such as Anolis sagrei sagrei.

Examples of Linnaean Taxonomy[edit]

The usual classifications of five species follow: the fruit fly, so familiar in genetics laboratories (Drosophila melanogaster), humans (Homo sapiens), the peas used by Gregor Mendel in his discovery of genetics (Pisum sativum), the "fly agaric" mushroom Amanita muscaria, and the bacterium Escherichia coli. The eight major ranks are given in bold; a selection of minor ranks are given as well.

Rank Fruit Fly Human Pea Fly Agaric E. coli
Domain Eukarya Eukarya Eukarya Eukarya Bacteria
Kingdom Animalia Animalia Plantae Fungi
Phylum or Division Arthropoda Chordata Magnoliophyta Basidiomycota Proteobacteria
Subphylum or subdivision Hexapoda Vertebrata Magnoliophytina Hymenomycotina
Class Insecta Mammalia Magnoliopsida Homobasidiomycetae Gammaproteobacteria
Subclass Pterygota Theria Magnoliidae Hymenomycetes
Order Diptera Primates Fabales Agaricales Enterobacteriaceae
Suborder Brachycera Haplorrhini Fabineae Agaricineae
Family Drosophilidae Hominidae Fabaceae Amanitaceae Enterobacteriaceae
Subfamily Drosophilinae Homininae Faboideae Amanitoideae
Genus Drosophila Homo Pisum Amanita Escherichia
Species Drosophila melanogaster Homo sapiens Pisum sativum Amanita muscaria Escherichia coli

Table Notes:

  • The ranks of higher taxa, especially intermediate ranks, are prone to revision as new information about relationships is discovered. For example, the traditional classification of primates (class Mammalia — subclass Theria — infraclass Eutheria — order Primates) has been modified by new classifications such as McKenna and Bell (class Mammalia — subclass Theriformes — infraclass Holotheria) with Theria and Eutheria assigned lower ranks between infraclass and the order Primates. See mammal classification for a discussion. These differences arise because there are only a small number of ranks available and a large number of branching points in the fossil record.
  • Within species further units may be recognised. Animals may be classified into subspecies (for example, Homo sapiens sapiens, modern humans) or morphs (for example Corvus corax varius morpha leucophaeus, the Pied Raven). Plants may be classified into subspecies (for example, Pisum sativum subsp. sativum, the garden pea) or varieties (for example, Pisum sativum var. macrocarpon, snow pea), with cultivated plants getting a cultivar name (for example, Pisum sativum var. macrocarpon 'Snowbird'). Bacteria may be classified by strains (for example Escherichia coli, a strain that can cause food poisoning).

Terminations of names (suffixes)[edit]

Taxon above the genus level are often given names based on the type genus, with a standard termination. The terminations used in forming these names depend on the kingdom, and sometimes the phylum and class, as set out in the table below.

Rank Plants Algae Fungi Animals Bacteria[1]
Division/Phylum -phyta -mycota
Subdivision/Subphylum -phytina -mycotina
Class -opsida -phyceae -mycetes -ia
Subclass -idae -phycidae -mycetidae -idae
Superorder -anae
Order -ales -ales
Suborder -ineae -ineae
Infraorder -aria
Superfamily -acea -oidea
Epifamily -oidae
Family -aceae -idae -aceae
Subfamily -oideae -inae -oideae
Infrafamily -odd
Tribe -eae -ini -eae
Subtribe -inae -ina -inae
Infratribe -ad

Table notes:

  • In botany and mycology names at the rank of family and below are based on the name of a genus, sometimes called the type genus of that taxon, with a standard ending. For example, the rose family Rosaceae is named after the genus Rosa, with the standard ending "-aceae" for a family. Names above the rank of family are formed from a family name, or are descriptive (like Gymnospermae or Fungi).
  • For animals, there are standard suffixes for taxa only up to the rank of superfamily.[2]
  • Forming a name based on a generic name may be not straightforward. For example, the Latin "homo" has the genitive "hominis", thus the genus "Homo" (human) is in the Hominidae, not "Homidae".
  • The ranks of epifamily, infrafamily and infratribe (in animals) are used where the complexities of phyletic branching require finer-than-usual distinctions. Although they fall below the rank of superfamily, they are not regulated under the International Code of Zoological Nomenclature and hence do not have formal standard endings. The suffixes listed here are regular, but informal.[3]

  • Phylum Protozoa
  • Subphylum Plasmodroma
  • Class Mastigophora
  • Subclass Phytomastigina
  • Order Chloromonadina
  • Subclass Zoomastigina
  • Order Hypermastigina
  • Class Sporozoa
  • Subclass Cnidosporidia
  • Order Actinomyxidia
  • Subclass Haplosporidia
  • Subclass Sarcosporidia
  • Subclass Telosporidia
  • Order Coccidia
  • Class Sarcodina
  • Order Amoebina
  • Subphylum Ciliophora
  • Class Ciliata
  • Subclass Protociliata
  • Subclass Euciliata
  • Order Chonotricha
  • Order Holotricha
  • Suborder Apostomea
  • Order Peritricha
  • Suborder Sessilia
  • Order Spirotricha
  • Suborder Ctenostomata
  • Class Suctoria
  • Phylum Prolifera
  • Class Calcarea
  • Order Homocoela
  • Class Hexactinellida
  • Order Hexasterophora
  • Class Demospongiae
  • Subclass Tetractinellida
  • Phylum Coelenterata
  • Class Hydrozoa
  • Order Hydroida
  • Suborder Anthomedusae
  • Order Hydrocorallina
  • Suborder Milleporina
  • Order Trachylina
  • Suborder Trachymedusae
  • Order Siphonophora
  • Class Scyphozoa
  • Order Stauromedusae
  • Order Cubomedusae
  • Order Coronatae
  • Order Discomedusae
  • Suborder Semaeostomae
  • Class Anthozoa
  • Subclass Alcyonaria
  • Order Alcyonacea
  • Subclass Zoantharia
  • Order Actiniaria
  • Suborder Actinaria
  • Order Madreporaria
  • Order Zonanthidea
  • Order Antipatharia
  • Order Ceriantharia


  1. Bacteriologocal Code (1990 Revision)
  2. ICZN article 27.2
  3. As supplied by Eugene S. Gaffney & Peter A. Meylan (1988), "A phylogeny of turtles", in M.J. Benton (ed.), The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds 157-219 (Oxford: Clarendon Press).
Bacteriologocal Code (1990 Revision)

Jump up ↑ ICZN article 27.2 Jump up ↑ As supplied by Eugene S. Gaffney & Peter A. Meylan (1988), "A phylogeny of turtles", in M.J. Benton (ed.), The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds 157-219 (Oxford: Clarendon Press).

Further reading and resources[edit]