Tautonymy (i.e., the usage of tautonyms) is permissible in zoological nomenclature (see List of tautonyms for examples), but tautonyms are considered illegitimate under the current nomenclature rules for botanical nomenclature (ICBN Art 23.4). One example of a botanical tautonym is Larix larix (L.) H.Karst (1881). The earliest name for the European larch is Pinus larix L. (1753) but Karsten did not agree with the placement of the species in Pinus and decided to move it to Larix. In making this new combination he created a tautonym, not acceptable under the rules (1906 onwards; the rules are retroactive). In such a case either the next earliest validly published name must be found, in this case Larix decidua Mill. (1768), or (in its absence) a new epithet must be published.
However, it is allowed for the genus and species names to mean the same, without being identical in spelling. For instance, Arctostaphylos uva-ursi means bearberry twice, in Greek and Latin respectively. There are also instances of a repeat of the genus name with a slight modification, such as Lycopersicon lycopersicum (Greek and latinized Greek, the former name for the tomato). Differences as small as a single letter are permissible, as in the Jujube shrub, Ziziphus zizyphus.
A tautonym is sometimes considered to be any word or term made from two identical parts or syllables, such as bonbon, da-da, or wikiwiki. The origin of this usage is uncertain, but it has been suggested that it is of relatively recent derivation, based on a loose understanding of the scientific usage. The general term in linguistics for such double words is reduplicants.