Undescribed Taxa: The Gap Between Species Discovery and Formal Naming
In the vast field of taxonomy—the science of naming, defining, and classifying organisms—there exists a significant category of life known as undescribed taxa. An undescribed taxon is a group, such as a species, that has been discovered by scientists but has not yet been formally described or named according to established nomenclature codes.
Until a formal description is published, these organisms lack an official scientific name. While researchers often use temporary, informal labels to communicate their findings, these do not hold official standing. In some cases, a name may be published but fail to meet the strict requirements of the nomenclature codes; such a name is referred to as a nomen nudum (a "naked name").
Depending on the level of information available, an undescribed species is typically denoted by its genus name followed by "sp.". If multiple undescribed species exist within a single genus, they are often distinguished by letters or numbers. For example, the shark genus Pristiophorus once included four undescribed species labeled Pristiophorus sp. A, B, C, and D. By 2008, sp. A and sp. B were formally described as Pristiophorus peroniensis and P. delicatus, respectively.
Key Facts
- Definition: An undescribed taxon is a discovered species that lacks a formal scientific description and name.
- The Taxonomic Impediment: The average time from the initial discovery of a species to its formal description is between 13 and 21 years.
- Marine Biodiversity: While over 246,000 marine species are described, total estimates range from several hundred thousand to multiple millions.
- Molecular Tools: DNA barcoding helps identify "dark taxa"—genetically distinct organisms that lack formal names.
- Nomen Nudum: A published name that is invalid because the taxon was not adequately described.
Modern Context and the Taxonomic Impediment
The pace of discovery has accelerated due to advances in molecular biology and image-based identification. One of the most significant breakthroughs is the identification of cryptic species—organisms that look identical physically (morphologically) but are genetically distinct.
Despite these tools, a widening gap exists between discovery and formal naming, a phenomenon known as the taxonomic impediment. This delay is driven by a shortage of taxonomic experts and the labor-intensive process required to prepare a formal description. This is particularly evident in marine environments, where the number of undescribed species is estimated to be massive.
Molecular Approaches to Identification
Modern science utilizes Molecular Operational Taxonomic Units (MOTUs), which are groups of organisms distinguished by DNA sequence similarity. In some environmental DNA studies, the number of MOTUs exceeds the number of described species by an order of magnitude.
DNA barcoding uses standardized genetic markers to identify species. When a sequence does not match any known species in a reference database, it is flagged as a potential undescribed species, often called "dark taxa." However, molecular data alone is usually insufficient for formal naming; traditional morphological analysis and ecological data are still required to finalize a description.
Provisional Naming Across Disciplines
Bacteriology
In bacteriology, a name is only valid if the bacteria are deposited in a Bacteriology Culture Collection. If this is impossible, the species is given the provisional status of Candidatus.
Botany
Botanists may use a specimen number from a herbarium or a provisional name enclosed in quotation marks. If the name is unpublished, the Latin term ineditus (or ined.) may be used. For instance, many species in the genus Polyscias have appeared in literature under such designations. Quotation marks can also indicate an illegitimate name, such as "Endressia" (sensu Whiffin), which was later replaced by Pendressia in 2018 after being identified as an illegitimate homonym.
Database Management of Undescribed Taxa
To maintain scientific rigor, biodiversity databases have created systems to track unnamed species. The World Register of Marine Species (WoRMS) uses categories such as "Temporary" to accommodate species of uncertain classification or those identified as distinct but not yet named.
The Global Biodiversity Information Facility (GBIF) and Ocean Biodiversity Information System (OBIS) use the Darwin Core standard, employing fields like "taxonConceptID" to track these specimens. A major challenge is that a single specimen may have different identifiers across GenBank, BOLD (Barcode of Life Data System), and published literature. To solve this, managers recommend standardized formats incorporating institutional collection codes to ensure data remains linked once a formal name is finally assigned.
| Term | Meaning | Context |
|---|---|---|
| Undescribed Taxon | Discovered but not formally named | General Taxonomy |
| Nomen Nudum | Published name lacking adequate description | Nomenclature Codes |
| Candidatus | Provisional status for uncultured bacteria | Bacteriology |
| MOTU | Group defined by DNA sequence similarity | Molecular Biology |
| Dark Taxa | Genetically distinct but unnamed sequences | DNA Barcoding |
Frequently Asked Questions
What is the difference between an undescribed species and a nomen nudum?
An undescribed species is one that has been discovered but not yet formally named or described. A nomen nudum is a name that has been published, but is considered invalid because it was not accompanied by an adequate scientific description.
Why does it take so long to formally describe a new species?
This delay, known as the taxonomic impediment, is caused by a shortage of trained taxonomic experts and the time-consuming nature of conducting morphological and ecological analyses required for a valid description.
What are cryptic species?
Cryptic species are organisms that appear morphologically identical to one another but are genetically distinct enough to be classified as separate species, often revealed through DNA analysis.
How do scientists name a species before it is officially described?
They typically use the genus name followed by "sp." (e.g., Genus sp.). If there are multiple unknown species in one genus, they may use letters or numbers, such as Genus sp. A and Genus sp. B.
What is a MOTU in molecular taxonomy?
A Molecular Operational Taxonomic Unit (MOTU) is a group of organisms clustered together based on the similarity of their DNA sequences, used to identify biodiversity that may not yet be described morphologically.