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.”.
Botany
Conservation
In botanical nomenclature, conservation is a nomenclatural procedure governed by Article 14 of the ICN. Its purpose is "to avoid disadvantageous nomenclatural changes entailed by the strict application of the rules, and especially of the principle of priority [...]" (Art. 14.1). Conservation is possible only for names at the rank of family, genus or species.
It may effect a change in original spelling, type, or (most commonly) priority. Conserved spelling (orthographia conservanda, orth. cons.) allows spelling usage to be preserved even if the name was published with another spelling: Euonymus (not Evonymus), Guaiacum (not Guajacum), etc. (see orthographical variant). Conserved types (typus conservandus, typ. cons.) are often made when it is found that a type in fact belongs to a different taxon from the description, when a name has subsequently been generally misapplied to a different taxon, or when the type belongs to a small group separate from the monophyletic bulk of a taxon. Conservation of a name against an earlier taxonomic (heterotypic) synonym (which is termed a rejected name, nomen rejiciendum, nom. rej.) is relevant only if a particular taxonomist includes both types in the same taxon.
Rejection
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.
Effects
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: A conserved family name is protected against all other family names based on genera that are considered by the taxonomist to be part of the same family. A conserved genus or species name is conserved against any homonyms, homotypic synonyms, and those specific heterotypic synonyms that are simultaneously declared nomina rejicienda (as well as their own homotypic synonyms). As taxonomic changes are made, other names may require new proposals for conservation and/or rejection.
Documentation
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.