Plant naming

Naming rules

This article is a plain english rewrite of the ninth edition of the International Code of Nomenclature for Cultivated Plants (ICNCP), which is the set of rules about how cultivated plants are named. Because it’s simplified, some information has been left out. This version is aimed at people who are naming new plants, or who want to understand how new plants get named. For an example, you can read more about the Tradescantia cultivar registration authory.

This rewrite doesn’t cover the rules about cultivar groups, grexes, or graft-chimeras. Some of the details about applying the rules to historic names have also been skipped or simplified. Read the full original version if you want to be sure of all the rules.


It’s important to have a system for giving names to plants. Names are for referring to plants, not for describing them or their origins. To make the system work, it’s important to publish and keep track of information about plants and their names.

A document called the ICNCP (nicknamed the Code) sets out the rules for a naming system. It isn’t a law, so nothing happens if people don’t follow it. But anyone involved with plants should follow it, because having a shared system is good for everyone. Experts from around the world have been agreed on these rules since the first version was made in 1953.

The Code gives the rules for naming cultivated plants – that means plants selected and grown deliberately by humans (for example gardens, farms, and houseplants). It doesn’t give rules about:

  • Naming wild plants. Those rules are separate, and given in the International Code of Nomenclature for algae, fungi, and plants (ICN).
  • Common names. Those are less precise names that people use day-to-day when talking about all kinds of plants (wild and cultivated).
  • Trade names. Those are names that people use to sell plants.
  • Statutory registration. Those are the laws that some countries have, to let people protect a new type of plant they made so that no-one can sell it without permission.

The Code is made by the International Society for Horticultural Science (ISHS). They decide the rules and help people follow them.

What is a cultivar?

A cultivar is a set of cultivated plants which all have some special features in common. The features can be anything (for example, certain flower colour, leaf shape, fruit flavour), as long as they are:

  • Distinct. The features make the set of plants different from any other.
  • Uniform. All plants in the set have the same features.
  • Stable. When new plants of the cultivar are made, they have the same features too.

A cultivar is defined by its special features, not by its origin. If two plants can’t be told apart by any of their features, they are the same cultivar – even if they came from different places or separate mutations. If a plant makes seedlings or a mutation and some of the new plants have different features, they are not the same cultivar.

Sometimes people mistakenly use the words “variety” or “form” instead of “cultivar”. A botanical variety (varietas or var.) and a botanical form (forma or f.) are sets of wild plants. They are defined by a different set of rules (separate from the Code), and they are not the same as cultivars. Unless a set of plants has been given a name by botanists studying wild plants, it should be treated as a cultivar.

The special features of a cultivar can be made in lots of different ways, for example:

  • They could come from a certain life stage of another plant (for example, an immature form, or a flowering part).
  • They could come from a mutated part of another plant (a sport).
  • They could be caused by a virus or other infection.
  • They could be caused by a chimera (when the plant has different genetics growing together).
  • They could be caused by a change in ploidy (when the plant has a different number of genes to normal).
  • They could be caused by genetic modification (when people change the genes of a plant with technology).
  • They could come from plants collected from a certain place in the wild.
  • They could be made by selective breeding.

Propagating means making new plants from existing ones. Different cultivars can be propagated in different ways, for example:

  • Asexual propagation (cuttings and divisions).
  • Open-pollinated seeds (where plants are pollinated freely by wild insects).
  • Self-fertilised seeds (where plants pollinate themselves).
  • Seeds collected from a particular place.
  • Seeds from a cross between two other cultivars.

No matter how a cultivar was made or how it’s propagated, it has to be named according to the same rules.

Choosing names

The full name for a cultivar is made of:

  • The wild group it belongs to – at least the genus, but the species or a more precise group if possible. This name can be given in scientific (Latin) form, or as a clear common name.
  • The epithet, which is the part of the name chosen to identify the cultivar.

The most important rule for a new epithet is that it can’t be the same as another epithet which has already been used in the same genus (even if it was a different species). It’s okay if the epithet has been used in a different genus.

There are also some other rules to make sure epithets are suitable and easy to use:

  • They can’t be in Latin.
  • They can’t be more than 30 characters long.
  • They can’t be just a single letter or set of numbers.
  • They can’t include certain words – form, variety, cultivar, grex, group, hybrid, maintenance, mixture, selection, series, sport, strain, improved, transformed.
  • They only punctuation marks allowed are ‘ , . – / \ !
  • They can’t include the scientific or common names of any plant if it might cause confusion.
  • They can’t be too similar to an existing epithet in the same genus.
  • They can’t exaggerate features (like “best” or “biggest”).
  • They can’t be trademarked.
  • They aren’t allowed if the person who originally made the plant doesn’t want that name used.

The epithet is written in Title Case and in ‘Single Quotes’, and without the abbreviations cv. or var. Epithets shouldn’t be translated into other languages, but they can be transcribed or transliterated to different alphabets.

Sometimes people use names which don’t follow any of the rules when selling plants. They are called trade names, and they aren’t regulated by the Code. People should always put the correct name in brackets if they’re using a trade name that doesn’t follow the rules.

Cultivar registration and ICRAs

The ISHS sometimes chooses people or groups to act as International Cultivar Registration Authorities (ICRAs).

The ICRA keeps track of all the existing names and synonyms in a certain genus. If any names are confusing, repeated, or break the rules, the ICRA is in charge of deciding what’s correct. The ICRA is allowed to decide a name is correct even though it breaks the rules, if the name is widely used and the ICRA explains their decision. If someone disagrees with anything the ICRA decides, they can ask the ISHS to decide once and for all.

The ICRA is also in charge of registering new cultivars. If someone makes a new cultivar in that genus, they should give the ICRA information (like a description of the cultivar, and what name they choose), and the ICRA will publish and keep track of it. This makes it easier for anyone to publish a new cultivar, and for anyone to know what cultivars already exist. The ICRA doesn’t decide whether a new cultivar is good or distinct. Their job is just to keep track of all the names and how they are used.

If there’s no ICRA for a group, the rules are still the same. But they might be more difficult to follow or keep track of, because there’s no central register of all the correct names.

Making names official

This is how to make a new name official:

  • Choose a name that follows the rules
  • Describe its special features, and how to tell it apart from similar plants (this could include pictures)
  • Publish that information somewhere that’s:
    • Physical (on paper, not online)
    • Dated
    • Publicly available

Examples of ways to publish:

  • In a nursery catalog which gets given out to customers
  • In a gardening magazine or journal
  • Register the name with the ICRA and they will publish for you in their chosen publication

Once a name has been made official for a new plant, it’s the correct name. Each cultivar only has one correct name, but sometimes more than one name for the same cultivar gets made official. This is how to decide which one is the correct name:

  • Usually, whichever name was made official first is correct (this is called an accepted name).
  • If more than one name has been used for a long time, then the ICRA can decide the more popular one is correct even if it wasn’t the first one (this is called a conserved name).
  • If a name has been used for statutory registration, that name is correct even if it wasn’t the first one (this is called an adopted name).

Any name that has been made official but isn’t the correct one, is called a synonym. It refers to the same cultivar but you shouldn’t use it when you know the correct name.

Some of the rules were less strict in the past. So sometimes a name is correct now even though it breaks some of the rules, because it was allowed at the time it was made.

This article is a simplified summary of the rules for cultivar naming. To see all the rules in full, read the International Code of Nomenclature for Cultivated Plants (ICNCP).

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