In botanical nomenclature, autonyms are automatically created names, as regulated by the International Code of Nomenclature for algae, fungi, and plants that are created for certain subdivisions of genera and species, those that include the type of the genus or species. An autonym might not be mentioned in the publication that creates it as a side-effect. Autonyms "repeat unaltered" the genus name or species epithet of the taxon being subdivided, and no other name for that same subdivision is validly published (article 22.2). For example, Rubus subgenus Eubatus is not validly published, and the subgenus is known as Rubus subgen. Rubus.
Autonyms are cited without an author. The publication date of the autonym is taken to be the same as that of the subdivision(s) that automatically established the autonym, with some special provisions (the autonym is considered to have priority over the other names of the same rank established at the same time (article 11.6)).
Articles 6.8, 22.1-3 and 26.1-3 relate to establishing autonyms.
Autonyms are not created if the name of the genus or species being subdivided is illegitimate.
The definition of an autonym is in Art. 6.8 of the ICN:
The application of names of taxonomic groups is determined by means of nomenclatural types (Principle II of the ICN). For all taxa, nomenclatural types are preserved specimens or illustrations.
In the case of an infraspecific taxon, if a botanist described a new taxon and publishes a new name at infraspecific level, all elements that previously belonged to the species (and are not included in the newly described taxon) now become a new infraspecific taxon. But as neither the type nor the final epithet has changed, there is no need for a change in author citation.
The same goes for a subdivision of a genus. If a botanist creates a new subdivision of a genus, for example by dividing a large genus into two or more subgenera, sections, or series, then a new subdivision of the genus at each of the new ranks will share the type of the genus and have as its epithet the name of the genus.
As will be clear from the definition, an autonym can be one of two kinds:
The name of a subdivision of a genus that includes the type of the genus is not validly published if its epithet does not repeat the generic name unaltered, in other words: it may not be anything other than an autonym, for example