23.1. The name of a species is a binary combination consisting of the name of the genus followed by a single specific epithet in the form of an adjective, a noun in the genitive, or a word in apposition, or several words, but not a phrase name of one or more descriptive substantives and associated adjectives in the ablative (see Art. 23.6(a)), nor certain other irregularly formed designations (see Art. 23.6(c)). If an epithet consists of two or more words, these are to be united or hyphenated. An epithet not so joined when originally published is not to be rejected but, when used, is to be united or hyphenated, as specified in Art. 60.9.
23.2. The epithet in the name of a species may be taken from any source whatever, and may even be composed arbitrarily (but see Art. 60.1).
Ex. 1. Cornus sanguinea, Dianthus monspessulanus, Papaver rhoeas, Uromyces fabae, Fumaria gussonei, Geranium robertianum, Embelia sarasiniorum, Atropa bella-donna, Impatiens noli-tangere, Adiantum capillus-veneris, Spondias mombin (an indeclinable epithet).
23.3. Symbols forming part of specific epithets proposed by Linnaeus do not invalidate the relevant names but must be transcribed.
Ex. 2. Scandix pecten {o+} L. is to be transcribed as Scandix pecten-veneris; Veronica anagallis {o!} L. is to be transcribed as Veronica anagallis-aquatica.
23.4. The specific epithet may not exactly repeat the generic name with or without the addition of a transcribed symbol (tautonym).
Ex. 3. "Linaria linaria" and "Nasturtium nasturtium-aquaticum" are contrary to this rule and cannot be validly published.
23.5. The specific epithet, when adjectival in form and not used as a substantive, agrees grammatically with the generic name (see Art. 32.6).
Ex. 4. Helleborus niger L., Brassica nigra (L.) W. D. J. Koch, Verbascum nigrum L.; Vinca major L., Tropaeolum majus L.; Rubus amnicola Blanch. ("amnicolus"), the specific epithet being a Latin substantive; Peridermium balsameum Peck, but also Gloeosporium balsameae Davis, both derived from the epithet of Abies balsamea (L.) Mill., treated as a substantive in the second example.
23.6. The following designations are not to be regarded as specific names:
(a) Descriptive designations consisting of a generic name followed by a phrase name (Linnaean nomen specificum legitimum) of one or more descriptive substantives and associated adjectives in the ablative.
Ex. 5. Smilax "caule inermi" (Aublet, Hist. Pl. Guiane 2, Tabl.: 27. 1775) is an abbreviated descriptive reference to an imperfectly known species which is not given a binomial in the text but referred to merely by a phrase name cited from Burman.
(b) Other designations of species consisting of a generic name followed by one or more words not intended as specific epithets.
Ex. 6. Viola "qualis" (Krocker, Fl. Siles. 2: 512, 517. 1790); Urtica "dubia?" (Forsskål, Fl. Aegypt.-Arab.: cxxi. 1775), the word "dubia?" being repeatedly used in Forsskål's work for species which could not be reliably identified.
Ex. 7. Atriplex "nova" (Winterl, Index Hort. Bot. Univ. Hung.: fol. A [8] recto et verso. 1788), the word "nova" (new) being here used in connection with four different species of Atriplex. However, in Artemisia nova A. Nelson (in Bull. Torrey Bot. Club 27: 274. 1900), nova was intended as a specific epithet, the species having been newly distinguished from others.
Ex. 8. Cornus "gharaf" (Forsskål, Fl. Aegypt.-Arab.: xci, xcvi. 1775) is an interim designation not intended as a species name. An interim designation in Forsskål's work is an original designation (for an accepted taxon and thus not a "provisional name" as defined in Art. 34.1(b)) with an epithet-like vernacular which is not used as an epithet in the "Centuriae" part of the work. Elcaja "roka" (Forsskål, Fl. Aegypt.-Arab.: xcv. 1775) is another example of such an interim designation; in other parts of the work (p. c, cxvi, 127) this species is not named.
Ex. 9. In Agaricus "octogesimus nonus" and Boletus "vicesimus sextus" (Schaeffer, Fung. Bavar. Palat. Nasc. 1: t. 100. 1762; 2: t. 137. 1763), the generic names are followed by ordinal adjectives used for enumeration. The corresponding species were given valid names, A. cinereus Schaeff. and B. ungulatus Schaeff., in the final volume of the same work (1774).
(c) Designations of species consisting of a generic name followed by two or more adjectival words in the nominative case.
Ex. 10. Salvia "africana coerulea" (Linnaeus, Sp. Pl.: 26. 1753) and Gnaphalium "fruticosum flavum" (Forsskål, Fl. Aegypt.-Arab.: cxix. 1775) are generic names followed by two adjectival words in the nominative case. They are not to be regarded as species names.
Ex. 11. However, Rhamnus "vitis idaea" Burm. f. (Fl. Ind.: 61. 1768) is to be regarded as a species name, since the generic name is followed by a substantive and an adjective, both in the nominative case; these words are to be hyphenated (R. vitis-idaea) under the provisions of Art. 23.1 and Art. 60.9. In Anthyllis "Barba jovis" L. (Sp. Pl.: 720. 1753) the generic name is followed by substantives in the nominative and in the genitive case respectively, and they are to be hyphenated (A. barba-jovis). Likewise, Hyacinthus "non scriptus" L. (Sp. Pl.: 316. 1753), where the generic name is followed by a negative particle and a past participle used as an adjective, is corrected to H. non-scriptus, and Impatiens "noli tangere" L. (Sp. Pl.: 938. 1753), where the generic name is followed by two verbs, is corrected to I. noli-tangere.
Ex. 12. Similarly, in Narcissus "Pseudo Narcissus" L. (Sp. Pl.: 289. 1753) the generic name is followed by an independent prefix and a substantive in the nominative case, and the name is to be corrected to N. pseudonarcissus under the provisions of Art. 23.1 and Art. 60.9.
(d) Formulae designating hybrids (see Art. H.10.3).
23.7. Phrase names used by Linnaeus as specific epithets (nomina trivialia) are to be treated as orthographical errors to be corrected in accordance with later usage by Linnaeus himself.
Ex. 13. Apocynum "fol. [foliis] androsaemi" L. is to be cited as A. androsaemifolium L. (Sp. Pl.: 213. 1753 [corr. L., Syst. Nat., ed. 10, 2: 946. 1759]); and Mussaenda "fr. [fructu] frondoso" L., as M. frondosa L. (Sp. Pl.: 177. 1753 [corr. L., Syst. Nat., ed. 10, 2: 931. 1759]).
23.8. Where the status of a designation of a species is uncertain under Art. 23.6, established custom is to be followed (Pre. 10).
*Ex. 14. Polypodium "F. mas", P. "F.
femina", and P. "F. fragile" (Linnaeus,
Sp. Pl.: 1090-1091. 1753) are, in accordance with established
custom, to be treated as P. filix-mas L., P. filix-femina
L., and P. fragile L., respectively. Likewise, Cambogia
"G. gutta" is to be treated as C. gummi-gutta
L. (Gen. Pl.: [522]. 1754). The intercalations "Trich."
[Trichomanes] and "M." [Melilotus] in the
names of Linnaean species of Asplenium and Trifolium,
respectively, are to be deleted, so that names in the form Asplenium
"Trich. dentatum" and Trifolium "M. indica",
for example, are treated as A. dentatum L. and T. indicum
L. (Sp. Pl.: 765, 1080. 1753).
23A.1. Names of persons and also of countries and localities used in specific epithets should take the form of substantives in the genitive (clusii, porsildiorum, saharae) or of adjectives (clusianus, dahuricus) (see also Art. 60, Rec. 60C and D).
23A.2. The use of the genitive and the adjectival form of the same word to designate two different species of the same genus should be avoided (e.g. Lysimachia hemsleyana Oliv. and L. hemsleyi Franch.).
23A.3. In forming specific epithets, authors should comply also with the following suggestions:
(a) To use Latin terminations insofar as possible.
(b) To avoid epithets which are very long and difficult to pronounce in Latin.
(c) Not to make epithets by combining words from different languages.
(d) To avoid those formed of two or more hyphenated words.
(e) To avoid those which have the same meaning as the generic name (pleonasm).
(f) To avoid those which express a character common to all or nearly all the species of a genus.
(g) To avoid in the same genus those which are very much alike, especially those which differ only in their last letters or in the arrangement of two letters.
(h) To avoid those which have been used before in any closely allied genus.
(i) Not to adopt epithets from unpublished names found in correspondence, travellers' notes, herbarium labels, or similar sources, attributing them to their authors, unless these authors have approved publication (see Rec. 34A).
(j) To avoid using the names of little-known or very restricted
localities, unless the species is quite local.