What is Type Material?

Type material plays an intrinsic role in naming species. For any new species, scientists or reporting authors declare a “type.” They then deposit a specimen, or “type material,” in a publicly available biorepository. This “type material” is tied to the new species name and serves as a reference for future comparisons. Researchers can then use DNA sequences obtained from type material to identify other samples from the same species. NCBI currently uses such an approach to verify the taxonomic assignment of prokaryotic genomes. Genomes from type materials act as an unambiguous reference for a taxonomic name and play an important role in comparative genomics, especially for taxon verification or reclassification.

The term “type material,” as officially defined by the International Nucleotide Sequence Database Collaboration (INSDC), includes several variations on “type” as defined in the relevant codes of nomenclature, with “type material” collectively referring to all or to cases where the type is ambiguous at the time of labeling. One or more types are designated as an objective standard to fix the scientific name of a species or infraspecies (subspecies, variety, or forma). Some common kinds of type, the organisms to which they apply, and their definitions are as follows:

Culture from type (algae, plants, and fungi): This designation is used where one (or preferably more) living culture is extracted from the type.

Epitype (algae, plants, and fungi): In botanical nomenclature only, a type designated to expand on the original holotype concept under specific conditions. There should only be one epitype.

Holotype (eukaryotes): There is only one holotype, usually a single specimen, and the “name-bearer” of its described taxon. It serves as the standard to which all subsequent examples of the described taxon are compared.

Isotype (algae, plants, and fungi): One or more duplicate specimens from the holotype collection can be deposited in other institutions. Usually, the collection number is the same as the holotype, but the institution code must be different. “Iso” can be appended to other kinds of types to indicate duplicates, e.g., isosyntype. Isotype is not a formally accepted term in the ICZN.

Neotype (eukaryotes): If the holotype is lost or destroyed, a neotype specimen is designated from a collection considered to be representative of the original holotype. There is only one neotype.

Neotype strain (prokaryotes): The equivalent term to neotype used for prokaryotes.

Paratype (eukaryotes): One or more additional specimens chosen to further illustrate traits in the described taxon.

Reference material/reference strain (not designated in any code): The reference material and reference strain qualifiers are not types, but internal INSDC terms used to capture any reference strain or material exclusively of types.

Type material (all organisms, except viruses): Used in ambiguous cases and could potentially indicate any of the other types.

Type strain (prokaryotes): Equivalent term to holotype used for prokaryotes. There can be multiple co-identical type strains, cultured from a single source.

Generated November 25, 2024