Home » Gardening Information » Garden Botany

The Rules for Naming Plants

International Code of Botanical Nomenclature

Over the past 250 years, the botanical community has developed an elaborate system of rules for the proper naming of plants. Members of this community meet every six years to discuss changes to the published code of botanical nomenclature. The latest edition, the International Code of Botanical Nomenclature (Tokyo Code), was published in 1994.

The rules of botanical nomenclature are based on six broad principles:

  1. Independence Plant names and the rules that govern them are independent of animal and bacteria names or rules. This means that it is permissible for a plant to have a name that is also used for an animal. For example, Pieris is both a genus in the Ericaceae (heath family) and the genus of Cabbage White Butterfly (Pieris rapae).
  2. Types Names are based on their types. Every plant name is tied to a particular herbarium specimen called a type. A type is a specimen that a botanist designates as typical of what he or she believes a new species to be. Another botanist may not be able to understand the classification proposed by the first botanist but can always examine the type specimen and use that as a guide to applying the name. If the group is reorganized (say, two species are recognized where formerly only one was recognized), then the original name will refer to only one of the new species-that is, the new species that contains the type for that name. There are also many examples of names that have had to be changed because the type, after it had been examined, was found to belong to a different species. For instance, the small-headed aster of eastern North America had been called Aster vimineus, but the type of this name was shown to be a specimen of the goblet aster, Aster lateriflorus. Therefore, Aster vimineus can no longer be used for the small-headed aster, which is now called Aster racemosa.
  3. Priority The earliest name that is in accordance with the rules is the correct one. Botanists are notorious for their detailed knowledge of precisely when a book or paper was published. In some cases, a name has priority because it predates another by only a few days.
  4. Uniqueness There is only one correct name for any taxon. There are, however, examples of taxa that are treated by different authors as species or subspecies. But for any particular rank there is only one correct name. While any one author can recognize a taxon as a species or subspecies, the author cannot recognize a taxon as both a species and subspecies.
  5. Latin Names are treated as Latin. While many names are derived from languages other than Latin, they are treated as Latin. In other words, Latin rules of grammar are applied to these words. A specific epithet is usually an adjective modifying the genus (a noun) and must agree in number, gender, and so on.
  6. Retroactivity The rules are retroactive. Many names that were correct when published are made incorrect by retroactive changes in the rules.

International Code of Nomenclature for Cultivated Plants

During the past fifty years, a systematized set of rules for the naming of cultivated plants has been developed. The latest edition of the International Code of Nomenclature for Cultivated Plants was published in 1995. These rules apply to the cultivar portion of the name (the part in single quotes) and not the Latin portion. They have been developed around the following 12 principles:

  1. The Need for Rules A system for the naming of cultivated plants is essential for understanding and communication.
  2. Only the Cultivated Groups Are Governed These rules only govern the naming of cultivated plants; the Latin portion of the name is governed by the Botanical Code.
  3. The Importance of Standards Preservation of standards (such as herbarium specimens, photos, and descriptive information) is important for stabilizing the naming of cultivated plants.
  4. Precedence The first cultivar name used is the correct one.
  5. Uniqueness For any particular group, there is only one correct name.
  6. Universality The cultivar names must not be trademarks or otherwise restricted in use.
  7. Legal Terms Take Precedence This code does not regulate the use of terms for cultivated plants defined under national and international legislation but rather recognizes that these legal terms take precedence.
  8. Unacceptability of Trade Designations Trade designations cannot be used as replacements for cultivar names.
  9. Common Names Are Not Regulated Common names are not regulated by the code.
  10. Registration Cultivar names should be registered.
  11. Free Assent The rules have no force of law. The code is enforced only by the free assent of the users.
  12. Retroactivity The rules are retroactive.

Registration Authorities for Cultivated Plants

Most cultivated plants have one or more societies or individuals who register the cultivar names. These international registration authorities (IRAs) check to make sure that the name is in accordance with the International Code of Botanical Nomenclature and the International Code of Nomenclature for Cultivated Plants. They often publish lists of the cultivars for their group and make them available upon request. Here is a list of the current registration authorities or their North American representative (for a complete listing see International Code of Nomenclature for Cultivated Plants, in "Further Reading").