NOMENCLATURE OF TAXA ACCORDING TO THEIR RANK
NAMES OF SPECIES
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 (see also Art. 23.6). If an epithet consisted originally 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. 60.11.
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. Adiantum capillus-veneris, Atropa bella-donna, Cornus sanguinea, Dianthus monspessulanus, Embelia sarasiniorum, Fumaria gussonei, Geranium robertianum, Impatiens noli-tangere, Papaver rhoeas, Spondias mombin (an indeclinable epithet), Uromyces fabae.
23.3. Symbols forming part of specific epithets proposed by Linnaeus do not prevent valid publication of the relevant names but must be transcribed.
Ex. 2. Scandix ‘pecten ♀’ L. is to be transcribed as Scandix pecten-veneris; Veronica ‘anagallis ’ L. is to be transcribed as Veronica anagallis-aquatica.
23.4. The specific epithet, with or without the addition of a transcribed symbol, may not exactly repeat the generic name (a designation formed by such repetition is a tautonym).
Ex. 3. “Linaria linaria” and “Nasturtium nasturtium-aquaticum” are tautonyms and cannot be validly published.
Ex. 4. Linum radiola L. (Sp. Pl.: 281. 1753) when transferred to Radiola Hill may not be named “Radiola radiola”, as was done by Karsten (Deut. Fl.: 606. 1882), because that combination is a tautonym and cannot be validly published. The next earliest name, L. multiflorum Lam. (Fl. Franç. 3: 70. 1779), is an illegitimate superfluous name for L. radiola. Under Radiola, the species has been given the legitimate name R. linoides Roth (Tent. Fl. Germ. 1: 71. 1788).
23.5. The specific epithet, when adjectival in form and not used as a noun, agrees with the gender of the generic name; when the epithet is a noun in apposition or a genitive noun, it retains its own gender and termination irrespective of the gender of the generic name. Epithets not conforming to this rule are to be corrected (see Art. 32.2) to the proper form of the termination (Latin or transcribed Greek) of the original author(s). In particular, the usage of the word element ‑cola as an adjective is a correctable error.
Ex. 5. Names with Latin adjectival epithets: Helleborus niger L., Brassica nigra (L.) W. D. J. Koch, Verbascum nigrum L.; Rumex cantabricus Rech. f., Daboecia cantabrica (Huds.) K. Koch (Vaccinium cantabricum Huds.); Vinca major L., Tropaeolum majus L.; Bromus mollis L., Geranium molle L.; Peridermium balsameum Peck, derived from the epithet of Abies balsamea (L.) Mill. treated as an adjective.
Ex. 6. Names with transcribed Greek adjectival epithets: Brachypodium distachyon (L.) P. Beauv. (Bromus distachyos L.); Oxycoccus macrocarpos (Aiton) Pursh (Vaccinium macrocarpon Aiton).
Ex. 7. Names with a noun for an epithet: Convolvulus cantabrica L., Gentiana pneumonanthe L., Liriodendron tulipifera L., Lythrum salicaria L., Schinus molle L., all with epithets featuring pre-Linnaean generic names. Gloeosporium balsameae Davis, derived from the epithet of Abies balsamea (L.) Mill. treated as a noun.
Ex. 8. Correctable errors in Latin adjectival epithets: Zanthoxylum trifoliatum L. (Sp. Pl.: 270. 1753) upon transfer to Acanthopanax (Decne. & Planch.) Miq. (m, see Art. 62.2(a)) is correctly A. trifoliatus (L.) Voss (Vilm. Blumengärtn., ed. 3: 1: 406. 1894, ‘trifoliatum’); Mimosa latisiliqua L. (Sp. Pl.: 519. 1753) upon transfer to Lysiloma Benth. (n) is correctly L. latisiliquum (L.) Benth. (in Trans. Linn. Soc. London 30: 534. 1875, ‘latisiliqua’); Corydalis chaerophylla DC. (Prodr. 1: 128. 1824) upon transfer to Capnoides Mill. (f, see Art. 62.4) is correctly Capnoides chaerophylla (DC.) Kuntze (Revis. Gen. Pl. 1: 14. 1891, ‘chaerophyllum’).
Ex. 9. Correctable errors in transcribed Greek adjectival epithets: Andropogon distachyos L. (Sp. Pl.: 1046. 1753, ‘distachyon’), nom. cons.; Bromus distachyos L. (Fl. Palaest.: 13. 1756) upon transfer to Brachypodium P. Beauv. (n) is correctly B. distachyon (L.) P. Beauv. (Ess. Agrostogr.: 155. 1812, ‘distachyum’) or to Trachynia Link (f) is correctly T. distachyos (L.) Link (Hort. Berol. 1: 43. 1827, ‘distachya’); Vaccinium macrocarpon Aiton (Hort. Kew. 2: 13. 1789) upon transfer to Oxycoccus Hill (m) is correctly O. macrocarpos (Aiton) Pursh (Fl. Amer. Sept. 1: 263. 1813, ‘macrocarpus’) or to Schollera Roth (f) is correctly S. macrocarpos (Aiton) Steud. (Nomencl. Bot. 746. 1821, ‘macrocarpa’).
Ex. 10. Correctable errors in epithets that are nouns: the epithet of Polygonum segetum Kunth (in Humboldt & al., Nov. Gen. Sp. 2, ed. qu.: 177. 1817) is a genitive plural noun (of the corn fields); when Small (Fl. S.E. U.S.: 378. 1903) proposed the new combination Persicaria ‘segeta’, it was a correctable error for Persicaria segetum (Kunth) Small. In Masdevallia echidna Rchb. f. (in Bonplandia 3: 69. 1855), the epithet corresponds to the generic name of an animal; when Garay (in Svensk Bot. Tidskr. 47: 201. 1953) proposed the new combination Porroglossum ‘echidnum’, it was a correctable error for P. echidna (Rchb. f.) Garay.
Ex. 11. Correctable error in the usage of ‑cola as an adjective: when Blanchard (in Rhodora 8: 170. 1906) proposed Rubus ‘amnicolus’, it was a correctable error for R. amnicola Blanch.
23.6. The following designations are not to be regarded as species names:
(a) Designations consisting of a generic name followed by a phrase name (Linnaean “nomen specificum legitimum”) commonly of one or more nouns and associated adjectives in the ablative case, but also including any single-word phrase names in works in which phrase names of two or more words predominate.
Ex. 12. 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.
Ex. 13. In Miller, The gardeners dictionary … abridged, ed. 4 (1754), phrase names of two or more words largely predominate over those that consist of a single word and that are thereby similar to Linnaean nomina trivialia (specific epithets) but are not distinguished typographically or in any other way from other phrase names. Therefore, designations in that work such as “Alkekengi officinarum”, “Leucanthemum vulgare”, “Oenanthe aquatica”, and “Sanguisorba minor” are not validly published names.
(b) Other designations of species consisting of a generic name followed by one or more words not intended as a specific epithet.
Ex. 14. Viola “qualis” [of what sort] (Krocker, Fl. Siles. 2: 512, 517. 1790). Urtica “dubia?” [doubtful] (Forsskål, Fl. Aegypt.-Arab.: cxxi. 1775); the word “dubia?” was repeatedly used in Forsskål’s work for species that could not be reliably identified.
Ex. 15. Atriplex “nova” (Winterl, Index Hort. Bot. Univ. Hung.: fol. A  recto et verso. 1788); the word “nova” (new) was here used in connection with four different species of Atriplex. However, in Artemisia nova A. Nelson (in Bull. Torrey Bot. Club 27: 274. 1900), the species was newly distinguished from others and nova was intended as a specific epithet.
Ex. 16. 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 not therefore a “provisional name” as defined in Art. 36.1(a)) with an epithet-like vernacular that 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 (pp. c, cxvi, 127) this species is not named.
Ex. 17. 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 validly published names, A. cinereus Schaeff. : Fr. and B. ungulatus Schaeff., in the final volume of the same work (l.c. 4: 100, 88. 1774).
Ex. 18. Honckeny (1782; see Art. 46 Ex. 47) used species designations such as, in Agrostis, “A. Reygeri I.”, “A. Reyg. II.”, “A. Reyg. III.” (all referring to species described but not named in Reyger, Tent. Fl. Gedan.: 36–37. 1763), and also “A. alpina. II” for a newly described species following after A. alpina Scop. These are informal designations used for enumeration, not validly published binomials; they may not be expanded into, e.g., “Agrostis reygeri-prima”.
(c) Designations of species consisting of a generic name followed by two or more adjectival words in the nominative case.
Ex. 19. “Salvia africana caerulea” (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. 20. Rhamnus ‘vitis idaea’ Burm. f. (Fl. Ind.: 61. 1768) is to be regarded as a species name because the generic name is followed by a noun 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 60.11. In Anthyllis ‘Barba jovis’ L. (Sp. Pl.: 720. 1753) the generic name is followed by a noun in the nominative case and a noun in the genitive case, 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. 21. In Narcissus ‘Pseudo Narcissus’ L. (Sp. Pl.: 289. 1753) the generic name is followed by a prefix (a word that cannot stand independently) and a noun in the nominative case, and the name is to be corrected to N. pseudonarcissus under the provisions of Art. 23.1 and 60.11.
(d) Formulae designating hybrids (see Art. H.10.2).
23.7. Phrase names used by Linnaeus as specific epithets (“nomina trivialia”) are to be corrected in accordance with later usage by Linnaeus himself (but see Art. 23.6(c)).
Ex. 22. Apocynum ‘fol. [foliis] androsaemi’ L. is cited as A. androsaemifolium L. (Sp. Pl.: 213. 1753 [corr. L., Syst. Nat., ed. 10: 946. 1759]); and Mussaenda ‘fr. [fructu] frondoso’ L., as M. frondosa L. (Sp. Pl.: 177. 1753 [corr. L., Syst. Nat., ed. 10: 931. 1759]).
*Ex. 23. 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.: . 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 nouns in the genitive (clusii, porsildiorum, saharae) or of adjectives (clusianus, dahuricus) (see also Art. 60, Rec. 60C, and 60D).
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:
(a) Use Latin terminations insofar as possible.
(b) Avoid epithets that are very long or difficult to pronounce in Latin.
(c) Not make epithets by combining words from different languages.
(d) Avoid those formed of two or more hyphenated words.
(e) Avoid those that have the same meaning as the generic name (pleonasm).
(f) Avoid those that express a character common to all or nearly all the species of a genus.
(g) Avoid in the same genus those that are very much alike, especially those that differ only in their last letters or in the arrangement of two letters.
(h) Avoid those that have been used before in any closely allied genus.
(i) Not 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. 50G).
(j) Avoid using the names of little-known or very restricted localities unless the species is quite local.