Basionym

In the scientific name of organisms, basionym or basyonym means the original name on which a new name is based; the author citation of the new name should include the authors of the basionym in parentheses. The term "basionym" is used in both botany and zoology. In zoology, alternate terms such as original combination or protonym are sometimes used instead. Bacteriology uses a similar term, basonym, spelled without an i.

Although "basionym" and "protonym" are often used interchangeably, they have slightly different technical definitions. A basionym is the correct spelling of the original name (according to the applicable nomenclature rules), while a protonym is the original spelling of the original name. These are typically the same, but in rare cases may differ.

When creating new taxonomic names, there are specific rules about how basionyms can be used. A new combination or name at new rank must be based directly on the original basionym rather than on any intermediate combinations. This means that if a species is transferred between multiple genera over time, each new combination must refer back to the original name rather than to more recent combinations. This helps maintain a clear chain of nomenclature and prevents confusion about the ultimate source of the name. For example, when transferring a species that has already been moved to a different genus, taxonomists must cite the original species name as the basionym, not the intermediate combination.