A conserved name or nomen conservandum (plural nomina conservanda, abbreviated as nom. cons.) is a scientific name that has specific nomenclatural protection. That is, the name is retained, even though it violates one or more rules which would otherwise prevent it from being legitimate. Nomen conservandum is a Latin term, meaning "a name to be conserved". The terms are often used interchangeably, such as by the International Code of Nomenclature for Algae, Fungi, and Plants (ICN), while the International Code of Zoological Nomenclature favours the term "conserved name".
The process for conserving botanical names is different from that for zoological names. Under the botanical code, names may also be "suppressed", nomen rejiciendum (plural nomina rejicienda or nomina utique rejicienda, abbreviated as nom. rej.), or rejected in favour of a particular conserved name, and combinations based on a suppressed name are also listed as “nom. rej.”.
In botanical nomenclature, conservation is a nomenclatural procedure governed by Article 14 of the ICN. Its purpose is
It may effect a change in original spelling, type, or (most commonly) priority.
Besides conservation of names of certain ranks (Art. 14), the ICN also offers the option of outright rejection of a name (nomen utique rejiciendum) also called suppressed name under Article 56, another way of creating a nomen rejiciendum that cannot be used anymore. Outright rejection is possible for a name at any rank.
Rejection (suppression) of individual names is distinct from suppression of works (opera utique oppressa) under Article 34, which allows for listing certain taxonomic ranks in certain publications which are considered not to include any validly published names.
Conflicting conserved names are treated according to the normal rules of priority. Separate proposals (informally referred to as "superconservation" proposals) may be made to protect a conserved name that would be overtaken by another. However, conservation has different consequences depending on the type of name that is conserved:
Conserved and rejected names (and suppressed names) are listed in the appendices to the ICN. As of the 2012 (Melbourne) edition, a separate volume holds the bulk of the appendices (except appendix I, on names of hybrids). The substance of the second volume is generated from a database which also holds a history of published proposals and their outcomes, the binding decisions on whether a name is validly published (article 38.4) and on whether it is a homonym (article 53.5). The database can be queried online.
In the course of time there have been different standards for the majority required for a decision. However, for decades the Nomenclature Section has required a 60% majority for an inclusion in the Code, and the Committees have followed this example, in 1996 adopting a 60% majority for a decision.
For zoology, the term "conserved name", rather than nomen conservandum, is used in the International Code of Zoological Nomenclature, although informally both terms are used interchangeably.
This is a more generalized definition than the one for nomen protectum, which is specifically a conserved name that is either a junior synonym or homonym that is in use because the senior synonym or homonym has been made a nomen oblitum ("forgotten name").
An example of a conserved name is the dinosaur genus name Pachycephalosaurus, which was formally described in 1943. Later, Tylosteus (which was formally described in 1872) was found to be the same genus as Pachycephalosaurus (a synonym). By the usual rules, the genus Tylosteus has precedence and would normally be the correct name. But the International Commission on Zoological Nomenclature (ICZN) ruled that the name Pachycephalosaurus was to be given precedence and treated as the valid name, because it was in more common use and better known to scientists.
The ICZN's procedural details are different from those in botany, but the basic operating principle is the same, with petitions submitted to the commission for review.