Basionym

In the scientific naming of organisms, a basionym or basyonym is 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

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. A basionym must therefore be legitimate. Basionyms are regulated by the code's articles 6.10, 7.3, 41, and others.

When a current name has a basionym, the author or authors of the basionym are included in parentheses at the start of the author citation. If a basionym is later found to be illegitimate, it becomes a replaced synonym and the current name's author citation must be changed so that the basionym authors do not appear.

Historical rules for basionyms have evolved over time. Prior to 1 January 1953, the requirements for referencing basionyms were less stringent: an indirect reference to a basionym or replaced synonym was sufficient for valid publication of a new combination, name at new rank, or replacement name. After this date, more explicit references became required. This change of rank from family to subfamily is an example of status novus (abbreviated stat. nov.), also called a "name at new rank".

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