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.
21.2. The epithet 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, but not a noun in the genitive singular. It is written with an initial capital letter (see
Art. 32.5 and 60.2).
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-.
Ex. 1. Costus subg. Metacostus; Ricinocarpos sect.
Anomodiscus; Valeriana sect. Valerianopsis; Euphorbia sect.
Tithymalus; Pleione subg. Scopulorum; Euphorbia subsect.
Tenellae; Sapium subsect. Patentinervia; Arenaria ser.
Anomalae; but not Carex sect. "Eucarex".
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. 53.4).
Note 2. The names of hybrids with the rank of a subdivision of a genus are formed according to the provisions of
Art. H.7.
21.4. The use of a binary combination instead of a subdivisional epithet is not admissible. Contrary to
Art. 32.1(b), names so constructed are validly published but are to be altered to the proper form without change of author citation or date of publication.
Ex. 2. 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.
Recommendation 21A
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.
Recommendation 21B
21B.1. The epithet in the name of a subgenus or section is preferably a noun, that in the name of a subsection or lower subdivision of a genus preferably a plural adjective.
21B.2. 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 which is identical with the name of such a genus.
21B.3. 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 this Code.
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