Tautonyms in Scientific Nomenclature
In the world of biological classification, names are more than just labels; they are precise tools used to categorize life. Most species follow binomial nomenclature, a system where a two-part name identifies an organism. However, some species possess a unique naming characteristic known as a tautonym.
A tautonym is a scientific name in which both parts of the name are spelled identically. For example, the black rat is known as Rattus rattus. In this structure, the first part represents the genus (the broader group), and the second part is the specific epithet (in botany and mycology) or the specific name (in zoology).
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Key Facts
- Definition: A scientific name where the genus and specific name are identical (e.g., Bison bison).
- Zoology: Tautonyms are permitted and often indicate that the species is the type species of its genus.
- Botany: Tautonyms are explicitly prohibited and are treated as invalid names.
- Bacteria: Tautonyms were banned between 1947 and 1975 but are now allowed.
- Viruses: Tautonyms are permitted under the code of nomenclature for viruses.
Tautonyms in Zoology
In zoological nomenclature, tautonymous names are fully permissible. This includes not only binomials but also trinomial names used for subspecies, such as Gorilla gorilla gorilla or Bison bison bison.
Tautonyms typically emerge in two ways: during the initial naming of a species or through reclassification. For instance, the hidden mirror skipper of Brazil was named Speculum speculum—derived from the Latin word for "mirror"—due to its shiny wing coloration. Conversely, the extinct kangaroo Nombe nombe became a tautonym in 2022 after being reclassified from Protemnodon nombe following a review of its dental attributes.
It is also possible for a species to lose its tautonym through reclassification. An example is Polyspila polyspila, which is now known as Calligrapha polyspila.
The Role of Type Species
In animal classification, a tautonym often implicitly indicates that the species is the type species of its genus. While this can also be signaled by using the epithets typus or typicus, the tautonym is a common, though not exclusive, indicator.
Botanical Nomenclature and Prohibitions
Unlike zoology, the rules for botanical nomenclature strictly prohibit tautonyms. While the official codes do not provide a specific reason for this ban, it is believed to have stemmed from concerns over a century ago regarding potential confusion when taxon names shared identical spelling and capitalization.
This rule is applied retroactively. For example, the European larch was once proposed as Larix larix in 1880 by Gustav Karl Wilhelm Hermann Karsten. Because this created a tautonym, the name was deemed invalid under rules established in 1906. Consequently, the next earliest valid name, Larix decidua Mill. (1768), was used instead.
Pleonasm and Modified Repetition
While identical spelling is banned in botany, pleonasm—where both parts of the name mean the same thing in different languages—is allowed. Examples include Arctostaphylos uva-ursi (meaning "bearberry" in both Greek and Latin) and Picea omorika (using Latin and Serbian terms for spruce).
Additionally, names that repeat the genus with slight modifications, such as Ziziphus zizyphus, are permitted under the Code of Nomenclature, despite some historical contention.
Current Trends and Proposals
The rigid stance on botanical tautonyms has recently been challenged. In April 2023, a proposal was submitted to allow tautonyms in botany on a non-retroactive basis. Proponents argue that since zoological and bacteriological codes have used tautonyms for decades without issue, adopting them would simplify the botanical code and preserve original epithets.
Summary of Tautonym Permissibility
| Organism Group | Tautonyms Allowed? | Notes |
|---|---|---|
| Animals (Zoology) | Yes | Includes subspecies (trinomials). |
| Bacteria/Prokaryotes | Yes | Prohibited only between 1947 and 1975. |
| Plants/Algae/Fungi | No | Explicitly prohibited; applied retroactively. |
| Viruses | Yes | Permitted by the viral nomenclature code. |
Frequently Asked Questions
What is a tautonym in biology?
A tautonym is a scientific name where the genus name and the specific epithet are spelled exactly the same, such as Rattus rattus.
Why are tautonyms banned in botany?
Although not explicitly detailed in current codes, the prohibition likely arose from historical concerns that identical spelling and capitalization in taxon names would cause confusion.
Can a species stop being a tautonym?
Yes. If a species is reclassified into a different genus, it may lose its tautonymous name. For example, Polyspila polyspila became Calligrapha polyspila.
What is the difference between a tautonym and a pleonasm?
A tautonym involves identical spelling (e.g., Bison bison), whereas a pleonasm involves names that mean the same thing but are spelled differently, often using different languages (e.g., Arctostaphylos uva-ursi).
Are tautonyms allowed for bacteria?
Yes, they are currently permitted for all bacteria and prokaryotes, although they were prohibited for a period between 1947 and 1975.