The type system is central to all taxonomy in botany and zoology. The point is to fix each name to a particular specimen. This is to make clear what is meant by the names. Thus genus and species names are attached to a particular specimen. There is also a written description published in a listed journal, together with an illustration. The idea is that what one person means by the names should be the same as what another person means by the names.
The type species of a genus is the species that has the same type (specimen) as the genus. For example, Malus sylvestris, the European Wild Apple, is the type species of the genus Malus.
According to a precise set of rules laid down by the ICZN and the IBC, the scientific name of every taxon is almost always based on one particular type specimen, or in some cases specimens. Types are usually physical specimens that are kept in a museum or herbarium research collection. Failing that, an image of an individual of that taxon has sometimes been designated as a type.
So, a type is one particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to show the defining features of that particular taxon.
A type description must include a diagnosis (typically, a discussion of similarities to and differences from closely related species), and an indication of where the type specimen or specimens are deposited for examination.
There are international codes which set out exactly how the naming of a type species is done.
- specimen: usually an actual example of the animal or plant which is being named
- International Commission on Zoological Nomenclature and International Botanical Congress
- For example, the International Code of Nomenclature for algae, fungi, and plants or the International Code of Zoological Nomenclature.