Article 5. Principle of Binominal Nomenclature.
5.1. Names of species. The scientific name of a species, and not of a taxon of any other rank, is a combination of two names (a binomen), the first being the generic name and the second being the specific name. The generic name must begin with an upper-case letter and the specific name must begin with a lower-case letter [Art. 28].
5.1.1. For the application of the Principle of Binominal Nomenclature to the availability of genus-group names published without associated nominal species and of subspecific names published in trinomina see Article 11.4.
5.1.2. For the application of the Principle of Binominal Nomenclature in the use of subgeneric names and names for aggregates of species and subspecies see Article 6.
5.2. Names of subspecies. The scientific name of a subspecies is a combination of three names (a trinomen, i.e. a binomen followed by a subspecific name) [Art. 11.4.2]. The subspecific name must begin with a lower-case letter [Art. 28].
5.3. Typographical signs and qualifying abbreviations excluded. A typographical sign such as ?, and an abbreviation such as aff., prox. or cf., when used to qualify the application of a scientific name, does not form part of the name of a taxon even when inserted between the components of a name.