CHAPTER III. NOMENCLATURE OF TAXA ACCORDING TO THEIR RANK
SECTION 5. NAMES OF TAXA BELOW THE RANK OF SPECIES
(INFRASPECIFIC TAXA)
24.1. The name of an infraspecific taxon is a combination of the name of a species and an infraspecific epithet. A connecting term is used to denote the rank.
Ex. 1. Saxifraga aizoon subf. surculosa Engl. & Irmsch. This taxon may also be referred to as Saxifraga aizoon var. aizoon subvar. brevifolia f. multicaulis subf. surculosa Engl. & Irmsch.; in this way a full classification of the subforma within the species is given, not only its name.
24.2. Infraspecific epithets are formed like specific epithets and, when adjectival in form and not used as nouns, they agree grammatically with the generic name (see Art. 32.5).
Ex. 2. Solanum melongena var. insanum Prain (Bengal Pl.: 746. 1903, "insana").
24.3. Infraspecific names with final epithets such as typicus, originalis, originarius, genuinus, verus, and veridicus, purporting to indicate the taxon containing the type of the name of the next higher taxon, are not validly published unless they are autonyms (Art. 26).
Ex. 3. Lobelia spicata "var. originalis" (McVaugh in Rhodora 38: 308. 1936) was not validly published (see Art. 26 Ex. 1).
24.4. The use of a binary combination instead of an infraspecific 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 the author citation or date of publication.
Ex. 4. Salvia grandiflora subsp. "S. willeana" (Holmboe in Bergens Mus. Skr., ser. 2, 1(2): 157. 1914) is to be cited as S. grandiflora subsp. willeana Holmboe.
Ex. 5. Phyllerpa prolifera var. "Ph. firma" (Kützing, Sp. Alg.: 495. 1849) is to be altered to P. prolifera var. firma Kütz.
Note 1. Infraspecific taxa within different species may bear names with the same final epithet; those within one species may bear names with the same final epithet as the names of other species (but see Rec. 24B.1).
Ex. 6. Rosa glutinosa var. leioclada H. Christ (in Boissier, Fl. Orient. Suppl.: 222. 1888) and Rosa jundzillii f. leioclada Borbás (in Math. Term. Közlem. 16: 376, 383. 1880) are both permissible, as is Viola tricolor var. hirta Ging. (in Candolle, Prodr. 1: 304. 1824), in spite of the previous existence of a species named Viola hirta L.
Note 2. Names of infraspecific taxa within the same species, even if they differ in rank, are homonyms if they have the same epithet but are based on different types (Art. 53.4).
Recommendation 24A
24A.1. Recommendations made for forming specific epithets (Rec. 23A) apply equally for infraspecific epithets.
Recommendation 24B
24B.1. Authors proposing new infraspecific names should avoid epithets previously used as specific epithets in the same genus.
24B.2. When an infraspecific taxon is raised to the rank of species, or the inverse change occurs, the final epithet of its name should be retained unless the resulting combination would be contrary to this Code.