Understanding Infraspecific Names in Botany
In the world of biological classification, a species is often the most familiar unit of organization. However, nature is rarely so simple. Many plants exhibit variations that are distinct enough to be recognized but not different enough to be classified as entirely separate species. To account for this, botanists use infraspecific names—scientific names for any taxon (a group of one or more populations of an organism) that falls below the rank of species.
The naming of these botanical taxa is strictly regulated by the International Code of Nomenclature for algae, fungi, and plants (ICN). This system ensures that scientists worldwide can communicate precisely about specific plant variations without confusion.
How Infraspecific Names are Constructed
According to Article 24 of the ICN, an infraspecific name is not a single word but a combination of elements. It consists of the species name followed by an infraspecific epithet (a descriptive term), separated by a connecting term that indicates the rank of the taxon.
The Anatomy of a Name
A full infraspecific name follows this specific order: genus name, specific epithet, connecting term, and infraspecific epithet.
In professional writing, it is customary to italicize the genus, the specific epithet, and the infraspecific epithet. The connecting term, however, remains in standard Roman type. For example, in the name Acanthocalycium klimpelianum var. macranthum:
- Genus: Acanthocalycium
- Specific epithet: klimpelianum
- Connecting term: var. (short for varietas or variety)
- Infraspecific epithet: macranthum
Common Ranks and Abbreviations
While the ICN allows for various ranks, there are several recommended abbreviations used to denote the level of the taxon. These ranks are organized hierarchically to show the degree of variation.
| Full Rank Name | Recommended Abbreviation | English Term |
|---|---|---|
| subspecies | subsp. | Subspecies |
| varietas | var. | Variety |
| subvarietas | subvar. | Subvariety |
| forma | f. | Form |
| subforma | subf. | Subform |
Historically, some names used Greek letters (such as α, β, or γ) or letters like "b" as connecting terms. While these are now deprecated, they remain legal and are important as basionyms (the original name on which a new name is based) for current species. In some rare cases, if a rank is not defined, the term "[unranked]" is used.
Rules for Legitimate Naming
For an infraspecific name to be considered legitimate, it must adhere to the strict rules of the ICN. This involves the use of "types" and specific rules regarding how names are repeated or shared.
The Role of the Type Specimen
Every botanical name is attached to a type, which is typically a preserved plant specimen stored in a herbarium. The type serves as the permanent reference point; if a scientist wants to determine if a plant belongs to a specific infraspecific taxon, they compare it to the original type specimen.
Autonyms and Homonyms
A unique feature of botanical nomenclature is the autonym. A species does not have to be divided into infraspecific taxa. However, if a botanist creates a subspecies, the type specimen of the original species automatically becomes the type for a new, automatically created name that repeats the specific epithet.
For example, if the species Poa secunda is divided to create the subspecies Poa secunda subsp. juncifolia, the original type specimen automatically becomes Poa secunda subsp. secunda.
Additionally, the ICN prevents homonyms—where two different taxa are accidentally given the same epithet. If this occurs, the earliest published name is the only legitimate one, and the newer name must be changed.
Botanical vs. Other Naming Systems
Botanical nomenclature differs significantly from the systems used for animals, bacteria, and cultivated plants.
Zoological Nomenclature
In zoology, names below the species rank use a trinomen (a three-part name). Unlike botany, zoology recognizes only one rank below species—the subspecies—and does not use a connecting term (like "subsp.") between the names.
Prokaryotic Nomenclature
The Prokaryotic Code, which split from the ICN in 1975, also only governs the subspecies rank. However, it allows for ungoverned subdivisions such as serovar (sv.) and pathovar (pv.). Authorship in this system is typically listed only for the infraspecific author (e.g., Bacillus subtilis subsp. spizizenii Nakamura et al. 1999).
Cultivated Plants (ICNCP)
Plants created for agriculture or horticulture, known as cultivars, are not regulated by the ICN but by the International Code of Nomenclature for Cultivated Plants (ICNCP). Cultivar names can be attached to any scientific name from the genus level down. For example, Achillea 'Cerise Queen' is a cultivar name attached to a genus.
Key Facts
- Governing Body: The ICN regulates names for algae, fungi, and plants.
- Structure: Infraspecific names combine the species name, a rank-indicating connecting term, and an infraspecific epithet.
- Formatting: Genus, specific epithet, and infraspecific epithet are italicized; the connecting term is not.
- Autonyms: When a species is divided into ranks, the original type automatically receives a repeating name (e.g., species species).
- Types: All legitimate names must be linked to a type specimen, usually kept in a herbarium.
- Distinction: Botanical names use connecting terms (var., subsp.), whereas zoological names (trinomens) do not.
Frequently Asked Questions
Can an infraspecific epithet be used on its own?
No. Just as a specific epithet cannot stand alone, an infraspecific epithet must be accompanied by the genus and species names to be valid. For example, you cannot refer to a variety simply as macranthum; you must use the full name or a recognized abbreviation like A. k. var. macranthum.
What happens if two different plants are given the same infraspecific name?
This creates a homonym. According to the ICN, the name that was published first is the legitimate one, and the later name must be replaced.
What is the difference between a variety and a subspecies?
Both are infraspecific ranks used to categorize variation. While the ICN provides abbreviations for both (var. and subsp.), the specific choice of rank often depends on the taxonomic judgment of the botanist regarding the nature of the variation.
How are authors credited in infraspecific names?
Authorship can be shown in two ways: by listing only the author of the final infraspecific epithet, or by listing the authors of both the species and the infraspecific epithet.
Are cultivated plants like garden roses covered by the ICN?
No. Cultivated plants (cultivars) are governed by the International Code of Nomenclature for Cultivated Plants (ICNCP), which has different rules than those used for wild botanical taxa.