For purposes of priority the date of a name is either the date attributed to it in an Adopted List of Protected Names (Art. 20) or, for unlisted names established prior to the relevant starting date for mandatory registration (Art. 5.2), the date on which it was validly published or became available under the relevant Special Code, or the date on which it was established, on or after that same date, under the BioCode. Limitations of priority that under the Special Codes affect names in certain groups or of certain categories, even if not provided for in the BioCode, still apply.
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Competing names are acceptable names with types that belong to the same taxon. At family-group, genus-group and species-group ranks, the choice between competing names of the same rank is governed by the principle of priority of establishment.
Note 1. Under the principle of co-ordinate status (Art. 6), co-ordinate names in the other rank of the same rank group are automatically established and accordingly take the same date in both ranks of the group.
For any taxon in one of the ranks of the family or genus group, the accepted name is the earliest acceptable one that competes at that rank, except in cases of limitation of precedence under Art. 20–24, or where Art. 31 applies.
For any species-group taxon, the accepted name is the combination of the final epithet of the earliest acceptable name that competes at that rank, with the accepted name of the genus or species to which it is assigned, except (a) in cases of limitation of precedence under Art. 20–24, or (b) if the resulting combination cannot become established under Art. 28.2, or (c) would be unacceptable as a later homonym as defined in Art. 18, or (d) if Art. 31 rules that a different combination be used.
When, for any taxon of the family group, genus group or species group, a choice is possible between acceptable names of equal date, or between final epithets of acceptable names of equal date, the first such choice to be published before the relevant starting date for mandatory registration (Art. 5.2) in conformity with the relevant Special Code, or if there is none, the first registered choice under the BioCode (Art. 12) establishes the precedence of the chosen name, and of any acceptable combination with the same type and final epithet at that rank, over the other competing name(s).
Names of organisms (animals and algae excepted) based on a non-fossil type take precedence over names of the same rank based on a fossil (or subfossil) type (see also Art. 31.2).
The principle of priority is not mandatory for names of taxa not belonging to the family group, genus group or species group.
Authors should follow the principle of priority also when it is not mandatory, unless the result would be nomenclaturally disruptive and contrary to established tradition.
In order to stabilise the nomenclatural status of names in current use, and to prevent their being displaced by names no longer in use, Lists of names and their attributes may, after apposite public review, be submitted to the ICB for adoption (see Div. III.9).
Ex. 1. The Approved Lists of Bacterial Names (see Rule 24a of the bacteriological Code) are, for all events and purposes, equivalent to the Adopted Lists provided for in the BioCode.
Once a List has been adopted, all listed names and their co-ordinate names are protected. A protected name is treated as if conserved against earlier homonyms and unlisted competing names; it is treated as established in the place and on the date cited in the list; and its type, when listed, its spelling and, if specified, its gender are treated as if conserved.