Unit 2: Taxonomic Hierarchy & Botanical Nomenclature

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Principles and Rules of ICN

The International Code of Nomenclature for algae, fungi, and plants (ICN) is the set of rules and recommendations dealing with the formal botanical names that are given to plants. Its intent is that each taxonomic group of plants has only one correct name that is accepted worldwide.

Core Principles of ICN

• Independence: Botanical nomenclature is independent of zoological and bacteriological nomenclature.
• Typification: The application of names of taxonomic groups is determined by means of nomenclatural types.
• Priority: The nomenclature of a taxonomic group is based upon priority of publication.
• Uniqueness: Each taxonomic group with a particular circumscription, position, and rank can bear only one correct name.
• Scientific Names: Scientific names of taxonomic groups are treated as Latin regardless of their derivation.

Ranks and Names

Taxonomic groups are treated in a hierarchical system of ranks. The primary ranks are Kingdom, Division, Class, Order, Family, Genus, and Species.

Suffixes for Specific Ranks

Typification and Author Citation

Typification

Typification is the process of designating a specific specimen (the type) to which the name of a taxon is permanently attached.

• Holotype: The single specimen designated by the author at the time of publication.
• Isotype: A duplicate specimen of the holotype, collected at the same time and place.
• Lectotype: A specimen chosen from the original material to serve as the type when no holotype was designated or is lost.
• Neotype: A specimen chosen to serve as the type when all original material is missing.

Author Citation

For a name to be complete and accurate, it should be followed by the name of the author who first validly published it. Example: Solanum tuberosum L. (where 'L.' stands for Linnaeus).

Valid Publication and Principle of Priority

Valid Publication

To be validly published, a name must be:

1. Effectively published (distributed in printed matter to the public/institutions).
2. Accompanied by a description or diagnosis of the taxon.
3. Formulated according to the rules of the ICN.

Principle of Priority

If a taxon has been given multiple names, the oldest validly published name is the correct one. This principle starts from May 1, 1753 (Linnaeus's Species Plantarum). Limitations: Priority does not apply to ranks above family.

Naming of Hybrids

Hybrids are named using an 'x' sign.

• Interspecific: Fragaria x ananassa (Hybrid between two species).
• Intergeneric: x Triticosecale (Hybrid between Triticum and Secale).

Taxonomic Documentation

Documentation is essential for storing and retrieving information about plant diversity.

• Flora: A book describing the plants of a specific geographical area (e.g., Flora of British India).
• Monograph: A comprehensive study of a single taxonomic group (usually a genus or family) across its entire global range.
• Journals: Periodical publications where new taxa are described and taxonomic research is shared.

Taxonomic Keys

Keys are artificial devices used for the rapid identification of plants.

• Single Access (Dichotomous) Keys: Provide two contrasting choices (couplets) at each step.
  • Indented Key: Each pair of choices is indented under the previous pair.
  • Bracketeded Key: The two choices of a couplet are placed on adjacent lines.
• Multi-access (Polyclave) Keys: Allow the user to choose characters in any order, often used in computer-based identification systems.

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