In zoological nomenclature, author citation refers to listing the person (or team) who first makes a scientific name of a taxon available. This is done in a scientific work while fulfilling the formal requirements under the International Code of Zoological Nomenclature ("the Code"). According to Article 51.1 of the Code, "the name of the author does not form part of the name of a taxon and its citation is optional, although customary and often advisable." However recommendation 51A suggests "the original author and date of a name should be cited at least once in each work dealing with the taxon denoted by that name. This is especially important and has a unique character between homonyms and in identifying species-group names which are not in their native combinations". For the sake of information retrieval, the author citation and year appended to the scientific name, e.g. genus-species-author-year, genus-author-year, family-author-year, etc., is often considered a "de facto" unique identifier, although this usage may often be imperfect. Rank matters The Code recognises three groups of names, according to rank: family-group names, at the ranks of superfamily, family, subfamily, tribe, subtribe (any rank below superfamily and above genus). genus-group names, at the ranks of genus and subgenus. species-group names, at the ranks of species and subspecies. Within each group, the same authorship applies regardless of the taxon level to which the name (with, in the case of a family-group name, the appropriate ending) is applied. For example, the taxa that the red admiral butterfly can be assigned to: Family: Nymphalidae Swainson, 1827 Subfamily: Nymphalinae Swainson, 1827 Tribe: Nymphalini Swainson, 1827 Genus: Vanessa Fabricius, 1807 Subgenus: Vanessa (Vanessa) Fabricius, 1807 Species: Vanessa atalanta (Linnaeus, 1758) Subspecies: Vanessa atalanta atalanta (Linnaeus, 1758) The parentheses around the author citation indicate that this was not the original taxonomic placement. In this case, Linnaeus published the name as Papilio atalanta Linnaeus, 1758. Identity of the author(s) The identity of the author had long been a matter of dispute and of secondary importance. In the first attempt to provide international rules for zoological nomenclature in 1895, the author was defined as the author of the scientific description, and not as the person who provided the name (published or unpublished), as had been usual practice in various animal groups before. This had the result that in some disciplines, for example in malacology, most taxonomic names had to change their authorship because they