NOMENCLATURE OF TAXA ACCORDING TO THEIR RANK
NAMES OF GENERA AND SUBDIVISIONS OF GENERA
21.1. The name of a subdivision of a genus is a combination of a generic name and a subdivisional epithet. A connecting term (subgenus, sectio, series, etc.) is used to denote the rank.
Note 1. Names of subdivisions of the same genus, even if they differ in rank, are homonyms if they have the same epithet but are based on different types (Art. 53.3), because the rank-denoting term is not part of the name.
21.2. The epithet in the name of a subdivision of a genus is either of the same form as a generic name, or a noun in the genitive plural, or a plural adjective agreeing in gender with the generic name (see Art. 32.2), but not a noun in the genitive singular. It is written with an initial capital letter (see Art. 60.2).
Ex. 1. Euphorbia sect. Tithymalus, Ricinocarpos sect. Anomodiscus; Pleione subg. Scopulorum; Arenaria ser. Anomalae, Euphorbia subsect. Tenellae, Sapium subsect. Patentinervia.
Ex. 2. In “Vaccinium sect. Vitis idaea” (Koch, Syn. Fl. Germ. Helv.: 474. 1837), the intended epithet consisted of two separate words unconnected by a hyphen; this is not therefore a validly published name (Art. 20.3 and 32.1(c); “Vitis idæa” is a pre-Linnaean, binary generic name). The name is correctly attributed to Gray (in Mem. Acad. Arts Sci., n.s., 3: 53. 1846) as Vaccinium sect. Vitis-idaea (hyphenated when published).
21.3. The epithet in the name of a subdivision of a genus is not to be formed from the name of the genus to which it belongs by adding the prefix Eu- (see also Art. 22.2).
Ex. 3. Costus subg. Metacostus; Valeriana sect. Valerianopsis; but not “Carex sect. Eucarex”.
21.4. A name with a binary combination instead of a subdivisional epithet, but otherwise in accordance with this Code, is treated as validly published in the form determined by Art. 21.1 without change of authorship or date.
Ex. 4. Sphagnum “b. Sph. rigida” (Lindberg in Öfvers. Förh. Kongl. Svenska Vetensk.-Akad. 19: 135. 1862) and S. sect. “Sphagna rigida” (Limpricht, Laubm. Deutschl. 1: 116. 1885) are to be cited as Sphagnum [unranked] Rigida Lindb. and S. sect. Rigida (Lindb.) Limpr., respectively.
Note 2. Names of hybrids at the rank of a subdivision of a genus are formed according to the provisions of Art. H.7.
21A.1. When it is desired to indicate the name of a subdivision of the genus to which a particular species belongs in connection with the generic name and specific epithet, the subdivisional epithet should be placed in parentheses between the two; when desirable, the subdivisional rank may also be indicated.
Ex. 1. Astragalus (Cycloglottis) contortuplicatus; A. (Phaca) umbellatus; Loranthus (sect. Ischnanthus) gabonensis.
21B.2. The epithet in the name of a subgenus or section is preferably a noun; that in the name of a subsection or lower-ranked subdivision of a genus is preferably a plural adjective.
21B.3. Authors, when proposing new epithets for names of subdivisions of genera, should avoid those in the form of a noun when other co-ordinate subdivisions of the same genus have them in the form of a plural adjective, and vice-versa. They should also avoid, when proposing an epithet for a name of a subdivision of a genus, one already used for a subdivision of a closely related genus, or one that is identical with the name of such a genus.
21B.4. When a section or a subgenus is raised to the rank of genus, or the inverse change occurs, the original name or epithet should be retained unless the resulting name would be contrary to the Code.