Understanding the International Code of Nomenclature for algae, fungi, and plants
In the scientific community, precision is everything. When a researcher in Japan and a botanist in Brazil discuss a specific organism, they must be certain they are talking about the exact same thing. To prevent confusion, the International Code of Nomenclature for algae, fungi, and plants (ICN or ICNafp) provides the essential set of rules and recommendations for naming these organisms. This system ensures that every taxonomic group—a specific group of organisms known as a taxon—has only one correct name accepted worldwide.
The ICN governs the formal names given to plants, fungi, and several other groups traditionally studied by botanists, phycologists (scientists who study algae), and mycologists (scientists who study fungi). This includes organisms like blue-green algae (Cyanobacteria), slime moulds, oomycetes, chytrids, and various photosynthetic protists. Because these terms represent traditional groups rather than formal biological clades (groups consisting of a common ancestor and all its descendants), they are written in lowercase within the Code's title.
Core Principles of Botanical Nomenclature
The ICN operates on several foundational principles to maintain global scientific consistency. Unlike the systems used for animals, bacteria, or viruses, botanical nomenclature is entirely independent. One of the most important rules is that all names are treated as Latin, regardless of their linguistic origin.
To ensure a name is permanently linked to a specific organism, the Code uses the type method. A name is fixed to a taxon by a type, which is almost always a specimen of dried plant material. These specimens are typically preserved in a herbarium—a specialized facility for storing dried plant collections—though they can also be preserved cultures or images. Many of these collections are now available for researchers to view online.
Another guiding principle is priority. This rule dictates that the first validly published name for a taxon is the correct one. For the purposes of botanical priority, the official starting point is May 1, 1753, which marks the publication of Species Plantarum by Carl Linnaeus.
While priority is a strict rule, the Code allows for the conservation of certain family, genus, and species names. This prevents the destabilization of scientific language that might occur if strict priority were enforced in every instance.
The Evolution of the Code
The history of botanical naming has been long and complex. Early efforts to standardize names were driven by dissatisfaction with the rules established in 1843 for zoological nomenclature. The first international set of rules, the Lois de la nomenclature botanique, was adopted in Paris in 1867. Unlike the modern Code, these early rules were largely recommendations rather than mandatory requirements for validly publishing a name.
Over the decades, various versions emerged, including the Vienna Rules of 1905 and the Cambridge Rules of 1935, eventually leading to the modern system. The Code is not static; it can only be changed by an International Botanical Congress (IBC), with the International Association for Plant Taxonomy providing the necessary infrastructure and support.
Major Modern Updates
The 18th International Botanical Congress, held in Melbourne in 2011, introduced several transformative changes to how science is conducted:
- Electronic Publication: The Code now permits the publication of new names in electronic-only formats, removing the old requirement to deposit physical paper copies in libraries.
- Language Flexibility: While Latin was once mandatory, the Code now allows for either English or Latin to be used for the essential descriptions or diagnoses of new names.
- Unified Naming: The "one fungus, one name" and "one fossil, one name" rules were implemented, eliminating the confusing distinction between different life stages (such as anamorph and teleomorph) of the same organism.
- Fungal Registration: To improve accuracy, new fungal descriptions must now include an identifier from a recognized repository, such as Index Fungorum, MycoBank, or Fungal Names.
Recent and Current Editions
The Code is updated periodically through new editions, each of which supersedes the previous one and is generally retroactive to 1753. The 17th edition, known as the Shenzhen Code, was adopted in July 2017 and published in June 2018. Following this, the 18th edition, the Madrid Code, was published in July 2025, incorporating decisions from the Twentieth IBC held in Madrid in 2024.
Key Facts
- Purpose: Provides standardized rules for naming algae, fungi, and plants.
- Governing Bodies: Managed by the International Botanical Congress (IBC) and supported by the International Association for Plant Taxonomy (IAPT).
- Starting Date: Botanical priority officially begins from May 1, 1753.
- Language: All taxonomic names are treated as Latin.
- Current Edition: The Madrid Code (published July 2025).
History of Code Versions
| Year of Publication | Informal Name |
|---|---|
| 1867 | Laws of botanical nomenclature |
| 1883 | Laws of botanical nomenclature, ed. 2 |
| 1906 | Vienna Rules |
| 1912 | Brussels Rules |
| 1935 | Cambridge Rules |
| 1950 | Amsterdam Code |
| 1952 | Stockholm Code |
| 1956 | Paris Code |
| 1961 | Montreal Code |
| 1966 | Edinburgh Code |
| 1972 | Seattle Code |
| 1978 | Leningrad Code |
| 1983 | Sydney Code |
| 1988 | Berlin Code |
| 1994 | Tokyo Code |
| 2000 | St Louis Code |
| 2006 | Vienna Code |
| 2012 | Melbourne Code |
| 2018 | Shenzhen Code |
| 2025 | Madrid Code (current) |
Frequently Asked Questions
What is the main purpose of the ICN?
The ICN ensures that every plant, fungus, and alga has one unique, universally accepted scientific name, which prevents confusion among researchers worldwide.
When did the rules for botanical naming officially begin?
For the purposes of determining name priority, the formal starting date is May 1, 1753, coinciding with the publication of Linnaeus's Species Plantarum.
Can new plant species be described in English?
Yes. Since the changes made at the Melbourne Congress in 2011, the Code allows for descriptions or diagnoses to be written in either English or Latin.
Is there a different code for plants grown in gardens?
Yes. The naming of cultivated plants is governed by a separate set of rules called the International Code of Nomenclature for Cultivated Plants, which supplements the ICN.
How are fungal names handled differently?
Modern rules follow the "one fungus, one name" principle, and new fungal descriptions are required to use identifiers from recognized repositories like MycoBank or Index Fungorum.