53.1. A name of a family, genus or species, unless conserved
(Art. 14) or sanctioned (Art.
15), is illegitimate if it is a later homonym, that is, if it is spelled exactly like a name based on a different type that was previously and validly published for a taxon of the same rank (see also
Art. 6 Note 1).
Ex. 1. The name Tapeinanthus Boiss. ex Benth. (1848), given to a genus of
Labiatae, is a later homonym of Tapeinanthus Herb. (1837), a name previously and validly published for a genus of
Amaryllidaceae. Tapeinanthus Boiss. ex Benth. is therefore unavailable for use. It was renamed
Thuspeinanta T. Durand (1888).
Ex. 2. The name Torreya Arn. (1838) is a nomen conservandum and is therefore available for use in spite of the existence of the earlier homonym
Torreya Raf. (1818).
Ex. 3. Astragalus rhizanthus Boiss. (1843) is a later homonym of the validly published name
Astragalus rhizanthus Royle (1835) and is therefore unavailable for use. Boissier renamed it
A. cariensis Boiss. (1849).
Note 1. A later homonym is unavailable for use even if the earlier homonym is illegitimate or is otherwise generally treated as a synonym.
Ex. 4. Zingiber truncatum S. Q. Tong (1987) is illegitimate, being a later homonym of
Z. truncatum Stokes (1812), even though the latter name is itself illegitimate under
Art. 52.1 because in its protologue the name
Amomum zedoaria Christm. (1779) was cited in synonymy.
Ex. 5. The name Amblyanthera Müll. Arg. (1860) is a later homonym of the validly published
Amblyanthera Blume (1849) and is therefore unavailable for use, although
Amblyanthera Blume is now considered to be a synonym of Osbeckia L. (1753).
53.2. A sanctioned name is illegitimate if it is a later homonym of another sanctioned name (see also
Art. 15 Note 1).
53.3. When two or more generic or specific names based on different types are so similar that they are likely to be confused (because they are applied to related taxa or for any other reason) they are to be treated as homonyms (see also
*Ex. 6. Names treated as homonyms: Asterostemma Decne. (1838) and
Astrostemma Benth. (1880); Pleuropetalum Hook. f. (1846) and Pleuripetalum T. Durand (1888);
Eschweilera DC. (1828) and Eschweileria Boerl. (1887); Skytanthus Meyen (1834) and
Scytanthus Hook. (1844).
*Ex. 7. The three generic names Bradlea Adans. (1763),
Bradleja Banks ex Gaertn. (1790), and Braddleya Vell. (1827), all commemorating Richard Bradley, are treated as homonyms because only one can be used without serious risk of confusion.
*Ex. 8. The names Acanthoica Lohmann (1902) and
Acanthoeca W. N. Ellis (1930), both designating flagellates, are sufficiently alike to be considered homonyms (Taxon 22: 313. 1973).
*Ex. 9. Epithets so similar that they are likely to be confused if combined under the same generic or specific name:
chinensis and sinensis; ceylanica and zeylanica; napaulensis, nepalensis, and
nipalensis; polyanthemos and polyanthemus; macrostachys and macrostachyus; heteropus and
heteropodus; poikilantha and poikilanthes; pteroides and pteroideus; trinervis and
trinervius; macrocarpon and macrocarpum; trachycaulum and trachycaulon.
*Ex. 10. Names not likely to be confused: Rubia L. (1753) and
Rubus L. (1753); Monochaetum (DC.) Naudin (1845) and Monochaete Döll (1875);
Peponia Grev. (1863) and Peponium Engl. (1897); Iris L. (1753) and
Iria (Pers.) Hedw. (1806); Desmostachys Miers (1852) and Desmostachya (Stapf) Stapf (1898);
Symphyostemon Miers (1841) and Symphostemon Hiern (1900); Gerrardina Oliv. (1870) and
Gerardiina Engl. (1897); Urvillea Kunth (1821) and Durvillaea
Bory (1826); Peltophorus Desv. (1810; Gramineae) and Peltophorum (Vogel) Benth. (1840;
Leguminosae); Senecio napaeifolius (DC.) Sch. Bip. (1845, "napeaefolius"; see
Art. 60 Ex. 14) and
S. napifolius MacOwan (1890; the epithets being derived, respectively, from
Napaea and Brassica napus); Lysimachia hemsleyana Oliv. (1891) and
L. hemsleyi Franch. (1895) (see, however, Rec.
23A.2); Euphorbia peplis L. (1753) and
E. peplus L. (1753).
Ex. 11. Names conserved against earlier names treated as homonyms (see
Lyngbya Gomont (vs. Lyngbyea Sommerf.); Columellia Ruiz & Pav. (vs.
Columella Lour.), both commemorating Columella, the Roman writer on agriculture;
Cephalotus Labill. (vs. Cephalotos Adans.); Simarouba Aubl. (vs.
53.4. The names of two subdivisions of the same genus, or of two infraspecific taxa within the same species, even if they are of different rank, are treated as homonyms if they have the same or a confusingly similar epithet and are not based on the same type.
Ex. 12. The names Andropogon sorghum subsp.
halepensis (L.) Hack. and A. sorghum var. halepensis (L.) Hack. (in Candolle & Candolle, Monogr. Phan. 6: 502. 1889) are legitimate, since both have the same type and the epithet may be repeated under
Ex. 13. Anagallis arvensis var. caerulea (L.) Gouan (Fl. Monsp.: 30. 1765), based on
A. caerulea L. (1759), makes illegitimate the name A. arvensis subsp.
caerulea Hartm. (Sv. Norsk Exc.-Fl.: 32. 1846), based on the later homonym
A. caerulea Schreber (1771).
Ex. 14. Scenedesmus armatus var. brevicaudatus (Hortob.) Pankow (in Arch. Protistenk. 132: 153. 1986), based on
S. carinatus var. brevicaudatus Hortob. (in Acta Bot. Acad. Sci. Hung. 26: 318. 1981), is a later homonym of
S. armatus f. brevicaudatus L. S. Péterfi (in Stud. Cercet. Biol. (Bucharest), Ser. Biol. Veg. 15: 25. 1963) even though the two names apply to taxa of different infraspecific rank.
Scenedesmus armatus var. brevicaudatus (L. S. Péterfi) E. H. Hegew. (in Arch. Hydrobiol. Suppl. 60: 393. 1982), however, is not a later homonym since it is based on the same type as
S. armatus f. brevicaudatus L. S. Péterfi.
Note 2. The same final epithet may be used in the names of subdivisions of different genera, and of infraspecific taxa within different species.
Ex. 15. Verbascum sect. Aulacosperma Murb. (Monogr. Verbascum: 34, 593. 1933) is permissible, although there is an earlier
Celsia sect. Aulacospermae Murb. (Monogr. Celsia: 34, 56. 1926). This, however, is not an example to be followed, since it is contrary to
53.5. When it is doubtful whether names or their epithets are sufficiently alike to be confused, a request for a decision may be submitted to the General Committee (see
Div. III), which will refer it for examination to the committee or committees for the appropriate taxonomic group or groups. A recommendation may then be put forward to an International Botanical Congress, and, if ratified, will become a binding decision.
Ex. 16. Names ruled as likely to be confused, and therefore to be treated as homonyms:
Ficus gomelleira Kunth (1847) and F. gameleira Standl. (1937) (Taxon 42: 111. 1993);
Solanum saltiense S. Moore (1895) and S. saltense (Bitter) C. V. Morton (1944) (Taxon 42: 434. 1993);
Balardia Cambess. (1829; Caryophyllaceae) and Ballardia Montrouz. (1860;
Myrtaceae) (Taxon 42: 434. 1993).
Ex. 17. Names ruled as not likely to be confused:
Cathayeia Ohwi (1931; Flacourtiaceae) and Cathaya Chun & Kuang (1962; fossil
Pinaceae) (Taxon 36: 429. 1987); Cristella Pat. (1887; Fungi) and
Christella H. Lév. (1915; Pteridophyta) (Taxon 35: 551. 1986); Coluria R. Br. (1823;
Rosaceae) and Colura (Dumort.) Dumort. (1835; Hepaticae) (Taxon 42: 433. 1993);
Acanthococcus Hook. f. & Harv. (1845; Rhodophyta) and Acanthococos Barb. Rodr. (1900;
Palmae) (Taxon 42: 433. 1993); Rauia Nees & Mart. (1823; Rutaceae) and
Rauhia Traub (1957; Amaryllidaceae) (Taxon 42: 433. 1993).
53.6. When two or more homonyms have equal priority, the first of them that is adopted in an effectively published text
(Art. 29, 30,
31) by an author who simultaneously rejects the other(s) is treated as having priority. Likewise, if an author in an effectively published text substitutes other names for all but one of these homonyms, the homonym for the taxon that is not renamed is treated as having priority.
Ex. 18. Linnaeus simultaneously published "10."
Mimosa cinerea (Sp. Pl.: 517. 1753) and "25." M. cinerea (Sp. Pl.: 520. 1753). In 1759, he renamed species 10
M. cineraria L. and retained the name M. cinerea for species 25, so that the latter is treated as having priority over its homonym.
Ex. 19. Rouy & Foucaud (Fl. France 2: 30. 1895) published the name
Erysimum hieraciifolium var. longisiliquum, with two different types, for two different taxa under different subspecies. Only one of these names can be maintained.
Note 3. A homonym renamed or rejected under Art. 53.6 remains legitimate and takes precedence over a later synonym of the same rank, should a transfer to another genus or species be effected.
Ex. 20. Mimosa cineraria L. (1759), based on M. cinerea L. (Sp. Pl.: 517 [non 520]. 1753; see Art. 53 Ex. 18), was transferred to Prosopis by Druce (1914) as P. cineraria (L.) Druce. However, the correct name in Prosopis is a combination based on M. cinerea.
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