Article 11

11.1. Each family or lower-ranked taxon with a particular circumscription, position, and rank can bear only one correct name. Special exceptions are made for nine families and one subfamily for which alternative names are permitted (see Art. 18.5 and 19.8). The use of separate names is allowed for fossil-taxa that represent different parts, life-history stages, or preservational states of what may have been a single organismal taxon or even a single individual (Art. 1.2).

Ex. 1. The generic name Sigillaria Brongn. (in Bull. Sci. Soc. Philom. Paris 1822: 26. 1822) was established for fossils of “bark” fragments, but Brongniart (in Arch. Mus. Hist. Nat. 1: 405. 1839) subsequently included stems with preserved anatomy within his concept of Sigillaria. Cones with preserved anatomy that may in part represent the same biological taxon are referred to as Mazocarpon M. J. Benson (in Ann. Bot. (Oxford) 32: 569. 1918), whereas such cones preserved as adpressions are known as Sigillariostrobus Schimp. (Traité Paléont. Vég. 2: 105. 1870). All these generic names can be used concurrently in spite of the fact that they may, at least in part, apply to the same organism.

11.2. A name has no priority outside the rank at which it is published (but see Art. 53.3).

Ex. 2. When Campanula sect. Campanopsis R. Br. (Prodr.: 561. 1810) is treated as a genus, it is called Wahlenbergia Roth (Nov. Pl. Sp.: 399. 1821), a name conserved against the heterotypic (taxonomic) synonym Cervicina Delile (Descr. Egypte, Hist. Nat.: 150. 1813), and not Campanopsis (R. Br.) Kuntze (Revis. Gen. Pl. 2: 378. 1891).

Ex. 3. Solanum subg. Leptostemonum Bitter (in Bot. Jahrb. Syst. 55: 69. 1919) is the correct name of the subgenus that includes its type, S. mammosum L., because it is the earliest available name at that rank. The homotypic S. sect. Acanthophora Dunal (Hist. Nat. Solanum: 131, 218. 1813), the inclusion of which caused the illegitimacy of S. sect. Leptostemonum Dunal (in Candolle, Prodr. 13(1): 29, 183. 1852), has no priority outside its own rank.

Ex. 4. Helichrysum stoechas subsp. barrelieri (Ten.) Nyman (Consp. Fl. Eur.: 381. 1879) when treated at specific rank is called H. conglobatum (Viv.) Steud. (Nomencl. Bot., ed. 2, 1: 738. 1840), based on Gnaphalium conglobatum Viv. (Fl. Libyc. Spec.: 55. 1824), and not H. barrelieri (Ten.) Greuter (in Boissiera 13: 138. 1967), based on G. barrelieri Ten. (Fl. Napol. 5: 220. 1835–1838).

Ex. 5. Magnolia virginiana var. foetida L. (Sp. Pl.: 536. 1753) when raised to specific rank is called M. grandiflora L. (Syst. Nat., ed. 10: 1082. 1759), not M. foetida (L.) Sarg. (in Gard. & Forest 2: 615. 1889).

Note 1. The provisions of Art. 11 determine priority between different names applicable to the same taxon; they do not concern homonymy.

11.3. For any taxon from family to genus, inclusive, the correct name is the earliest legitimate one with the same rank, except in cases of limitation of priority by conservation or protection (see Art. 14 and F.2) or where Art. 11.7, 11.8, 19.4, 56, 57, F.3, or F.7 apply.

Ex. 6. When Aesculus L. (Sp. Pl.: 344. 1753), Pavia Mill. (Gard. Dict. Abr., ed. 4: Pavia. 1754), Macrothyrsus Spach (in Ann. Sci. Nat., Bot., ser. 2, 2: 61. 1834), and Calothyrsus Spach (l.c.: 62. 1834) are referred to a single genus, its correct name is Aesculus.

11.4. For any taxon below the rank of genus, the correct name is the combination of the final epithet of the earliest legitimate name of the taxon at the same rank, with the correct name of the genus or species to which it is assigned, except (a) in cases of limitation of priority under Art. 14, 56, 57, F.2, F.3, or F.7, or (b) if Art. 11.7, 11.8, 22.1, or 26.1 rules that a different combination be used, or (c) if the resulting combination could not be validly published under Art. 32.1(c) or would be illegitimate under Art. 53. If (c) applies, the final epithet of the next earliest legitimate name at the same rank is to be used instead or, if there is no final epithet available, a replacement name or the name of a new taxon may be published.

Ex. 7. Primula sect. Dionysiopsis Pax (in Jahresber. Schles. Ges. Vaterländ. Kultur 87: 20. 1909) when transferred to Dionysia Fenzl becomes D. sect. Dionysiopsis (Pax) Melch. (in Mitt. Thüring. Bot. Vereins 50: 164–168. 1943); the replacement name D. sect. Ariadna Wendelbo (in Bot. Not. 112: 496. 1959) is illegitimate under Art. 52.1.

Ex. 8. Antirrhinum spurium L. (Sp. Pl.: 613. 1753) when transferred to Linaria Mill. is called L. spuria (L.) Mill. (Gard. Dict., ed. 8: Linaria No. 15. 1768).

Ex. 9. When transferring Serratula chamaepeuce L. (Sp. Pl.: 819. 1753) to Ptilostemon Cass., Cassini illegitimately (Art. 52.1) named the species P. muticus Cass. (in Cuvier, Dict. Sci. Nat. 44: 59. 1826). In Ptilostemon, the correct name is P. chamaepeuce (L.) Less. (Gen. Cynaroceph.: 5. 1832).

Ex. 10. The correct name for Rubus aculeatiflorus var. taitoensis (Hayata) T. S. Liu & T. Y. Yang (in Annual Taiwan Prov. Mus. 12: 12. 1969) is R. taitoensis Hayata var. taitoensis because R. taitoensis Hayata (in J. Coll. Sci. Imp. Univ. Tokyo 30(1): 96. 1911) has priority over R. aculeatiflorus Hayata (Icon. Pl. Formosan. 5: 39. 1915).

Ex. 11. When transferring Spartium biflorum Desf. (Fl. Atlant. 2: 133. 1798) to Cytisus Desf., Ball correctly proposed the replacement name C. fontanesii Spach ex Ball (in J. Linn. Soc., Bot. 16: 405. 1878) because of the previously and validly published C. biflorus L’Hér. (Stirp. Nov.: 184. 1791); the combination C. biflorus based on S. biflorum would be illegitimate under Art. 53.1.

Ex. 12. Spergula stricta Sw. (in Kongl. Vetensk. Acad. Nya Handl. 20: 235. 1799) when transferred to Arenaria L. is called A. uliginosa Schleich. ex Schltdl. (in Mag. Neuesten Entdeck. Gesammten Naturk. Ges. Naturf. Freunde Berlin 7: 207. 1808) because of the existence of the name A. stricta Michx. (Fl. Bor.-Amer. 1: 274. 1803), based on a different type; but on further transfer to the genus Minuartia L. the epithet stricta is again available and the species is called M. stricta (Sw.) Hiern (in J. Bot. 37: 320. 1899).

Ex. 13. Arum dracunculus L. (Sp. Pl.: 964. 1753) when transferred to Dracunculus Mill. is named D. vulgaris Schott (Melet. Bot. 1: 17. 1832). The use of the Linnaean epithet in Dracunculus would result in a tautonym (Art. 23.4), which would not be validly published (Art. 32.1(c)).

Ex. 14. Cucubalus behen L. (Sp. Pl.: 414. 1753) when transferred to Behen Moench was legitimately renamed B. vulgaris Moench (Methodus: 709. 1794) to avoid the tautonym “B. behen”. In Silene L., the epithet behen is unavailable because of the existence of S. behen L. (Sp. Pl.: 418. 1753). Therefore, the replacement name S. cucubalus Wibel (Prim. Fl. Werth.: 241. 1799) was proposed. This, however, is illegitimate (Art. 52.1) because the specific epithet vulgaris was available. In Silene, the correct name of the species is S. vulgaris (Moench) Garcke (Fl. N. Mitt.-Deutschland, ed. 9: 64. 1869).

Ex. 15. Helianthemum italicum var. micranthum Gren. & Godr. (Fl. France 1: 171. 1847) when transferred as a variety to H. penicillatum Thibaud ex Dunal retains its varietal epithet and is named H. penicillatum var. micranthum (Gren. & Godr.) Grosser (in Engler, Pflanzenr. IV. 193 (Heft 14): 115. 1903).

Ex. 16. The final epithet in the combination Thymus praecox subsp. arcticus (Durand) Jalas (in Veröff. Geobot. Inst. ETH Stiftung Rübel Zürich 43: 190. 1970), based on T. serpyllum var. arcticus Durand (Pl. Kaneanae Groenl.: 196. 1856), was first used at the rank of subspecies in the combination T. serpyllum subsp. arcticus (Durand) Hyl. (in Uppsala Univ. Årsskr. 1945(7): 276. 1945). However, if T. britannicus Ronniger (in Repert. Spec. Nov. Regni Veg. 20: 330. 1924) is included in this taxon, the correct name at subspecific rank is T. praecox subsp. britannicus (Ronniger) Holub (in Preslia 45: 359. 1973), for which the final epithet was first used at this rank in the combination T. serpyllum subsp. britannicus (Ronniger) P. Fourn. (Quatre Fl. France: 841. 1938, “S.-E. [Sous-Espèce] Th. Britannicus”).

Ex. 17. Transfer of Polypodium tenerum Roxb. (in Calcutta J. Nat. Hist. 4: 490. 1844) to Cyclosorus Link (Hort. Berol. 2: 128. 1833) would result in a later homonym due to the existence of C. tener (Fée) Christenh. (in Bot. J. Linn. Soc. 161: 250. 2009), based on Goniopteris tenera Fée (Mém. Foug. 11: 60. 1866). The correct name is a heterotypic synonym, C. ciliatus (Wall. ex Benth.) Panigrahi (in Res. J. Pl. Environm. 9: 66. 1993), based on the next earliest legitimate name of the taxon at the same rank, Aspidium ciliatum Wall. ex Benth. (Fl. Hongkong.: 455. 1861).

Note 2. The valid publication of a name at a rank lower than genus precludes any simultaneous homonymous combination (Art. 53), irrespective of the priority of other names with the same final epithet that may require transfer to the same genus or species.

Ex. 18. Tausch included two species in his new genus Alkanna: A. tinctoria Tausch (in Flora 7: 234. 1824), a new species based on “Anchusa tinctoria” in the sense of Linnaeus (Sp. Pl., ed. 2: 192. 1762), and A. matthioli Tausch (l.c. 1824), a replacement name based on Lithospermum tinctorium L. (Sp. Pl.: 132. 1753). Both names are legitimate and take priority from 1824.

Ex. 19. Raymond-Hamet transferred to the genus Sedum both Cotyledon sedoides DC. (in Mém. Agric. Econ. Soc. Agric. Seine 11: 11. 1808) and Sempervivum sedoides Decne. (in Jacquemont, Voy. Inde 4(Bot.): 63. 1844). He combined the epithet of the later name, Sempervivum sedoides, under Sedum, as S. sedoides (Decne.) Raym.-Hamet (in Candollea 4: 26. 1929), and published a replacement name, S. candollei Raym.-Hamet (l.c. 1929), for the earlier name. Both of Raymond-Hamet’s names are legitimate.

11.5. When, for any taxon at the rank of family or below, a choice is possible between legitimate names of equal priority at the corresponding rank, or between available final epithets of names of equal priority at the corresponding rank, the first such choice to be effectively published (Art. 29-31) establishes the priority of the chosen name, and of any legitimate combination with the same type and final epithet at that rank, over the other competing name(s) (but see Art. 11.6; see also Rec. F.5A.2).

Note 3. A choice as provided for in Art. 11.5 is effected by adopting one of the competing names, or its final epithet in the required combination, and simultaneously rejecting or relegating to synonymy the other(s) or their homotypic (nomenclatural) synonyms.

Ex. 20. When Dentaria L. (Sp. Pl.: 653. 1753) and Cardamine L. (l.c.: 654. 1753) are united, the resulting genus is called Cardamine because that name was chosen by Crantz (Cl. Crucif. Emend.: 126. 1769), who first united them.

Ex. 21. When Claudopus Gillet (Hyménomycètes: 426. 1876), Eccilia (Fr.:Fr.) P. Kumm. (Führer Pilzk.: 23. 1871), Entoloma (Fr. ex Rabenh.) P. Kumm. (l.c.: 23. 1871), Leptonia (Fr.:Fr.) P. Kumm. (l.c.: 24. 1871), and Nolanea (Fr.:Fr.) P. Kumm. (l.c.: 24. 1871) are united, one of the four generic names simultaneously published by Kummer must be used for the combined genus. Donk (in Bull. Jard. Bot. Buitenzorg, ser. 3, 18(1): 157. 1949) selected Entoloma, which is therefore treated as having priority over the other names.

Ex. 22. Brown (in Tuckey, Narr. Exped. Zaire: 484. 1818) was the first to unite Waltheria americana L. (Sp. Pl.: 673. 1753) and W. indica L. (l.c. 1753). He adopted the name W. indica for the combined species, and this name is accordingly treated as having priority over W. americana.

Ex. 23. Baillon (in Adansonia 3: 162. 1863), when uniting for the first time Sclerocroton integerrimus Hochst. (in Flora 28: 85. 1845) and S. reticulatus Hochst. (l.c. 1845), adopted the name Stillingia integerrima (Hochst.) Baill. for the combined taxon. Consequently Sclerocroton integerrimus is treated as having priority over S. reticulatus irrespective of the genus (Sclerocroton, Stillingia, or any other) to which the species is assigned.

Ex. 24. Linnaeus (Sp. Pl.: 902. 1753) simultaneously published the names Verbesina alba and V. prostrata. Later (Mant. Pl.: 286. 1771), he published Eclipta erecta, an illegitimate name because V. alba was cited in synonymy, and E. prostrata, based on V. prostrata. The first author to unite these taxa was Roxburgh (Fl. Ind., ed. 1832, 3: 438. 1832), who adopted the name E. prostrata (L.) L. Therefore, V. prostrata is treated as having priority over V. alba.

Ex. 25. Donia speciosa and D. formosa, which were simultaneously published by Don (Gen. Hist. 2: 468. 1832), were illegitimately renamed Clianthus oxleyi and C. dampieri, respectively, by Lindley (in Trans. Hort. Soc. London, ser. 2, 1: 522. 1835). Brown (in Sturt, Narr. Exped. C. Australia 2: 71. 1849) united both in a single species, adopting the illegitimate name C. dampieri and citing D. speciosa and C. oxleyi as synonyms; his choice is not of the kind provided for by Art. 11.5. Clianthus speciosus (G. Don) Asch. & Graebn. (Syn. Mitteleur. Fl. 6(2): 725. 1909), published with D. speciosa and C. dampieri listed as synonyms, is an illegitimate later homonym of C. speciosus (Endl.) Steud. (Nomencl. Bot., ed. 2, 1: 384. 1840); again, conditions for a choice under Art. 11.5 were not satisfied. Ford & Vickery (in Contr. New South Wales Natl. Herb. 1: 303. 1950) published the legitimate combination C. formosus (G. Don) Ford & Vickery and cited D. formosa and D. speciosa as synonyms, but because the epithet of the latter was unavailable in Clianthus Sol. ex Lindl. a choice was not possible and again Art. 11.5 does not apply. Thompson (in Telopea 4: 4. 1990) was the first to effect an acceptable choice when publishing the combination Swainsona formosa (G. Don) Joy Thomps. and indicating that D. speciosa was a synonym of it.

11.6. An autonym is treated as having priority over the name(s) of the same date and rank that upon their valid publication established the autonym (see Art. 22.3 and 26.3).

Note 4. When the final epithet of an autonym is used in a new combination under the requirements of Art. 11.6, the basionym of that combination is the name from which the autonym is derived, or its basionym if it has one.

Ex. 26. The publication of Synthyris subg. Plagiocarpus Pennell (in Proc. Acad. Nat. Sci. Philadelphia 85: 86. 1933) simultaneously established the autonym Synthyris Benth. (in Candolle, Prodr. 10: 454. 1846) subg. Synthyris. If Synthyris, including subg. Plagiocarpus, is recognized as a subgenus of Veronica L. (Sp. Pl.: 9. 1753), the correct name is V. subg. Synthyris (Benth.) M. M. Mart. Ort. & al. (in Taxon 53: 440. 2004), which has precedence over a combination in Veronica based on S. subg. Plagiocarpus.

Ex. 27. Heracleum sibiricum L. (Sp. Pl.: 249. 1753) includes H. sibiricum subsp. lecokii (Godr. & Gren.) Nyman (Consp. Fl. Eur.: 290. 1879) and H. sibiricum subsp. sibiricum automatically established at the same time. When H. sibiricum, so circumscribed, is included in H. sphondylium L. (l.c. 1753) as a single subspecies, the correct name of that subspecies is H. sphondylium subsp. sibiricum (L.) Simonk. (Enum. Fl. Transsilv.: 266. 1887), not “H. sphondylium subsp. lecokii”.

Ex. 28. The publication of Salix tristis var. microphylla Andersson (Salices Bor.-Amer.: 21. 1858) simultaneously established the autonym S. tristis Aiton (in Hort. Kew. 3: 393. 1789) var. tristis. If S. tristis, including var. microphylla, is recognized as a variety of S. humilis Marshall (Arbust. Amer.: 140. 1785), the correct name is S. humilis var. tristis (Aiton) Griggs (in Proc. Ohio Acad. Sci. 4: 301. 1905). However, if both these varieties of S. tristis are recognized as varieties of S. humilis, then the names S. humilis var. tristis and S. humilis var. microphylla (Andersson) Fernald (in Rhodora 48: 46. 1946) are used.

11.7. For purposes of priority, names of fossil-taxa (diatom taxa excepted) compete only with names based on a fossil type.

Ex. 29. The name Polysphaeridium zoharyi (M. Rossignol) J. P. Bujak & al. (in Special Pap. Palaeontol. 24: 34. 1980), based on Hystrichosphaeridium zoharyi M. Rossignol (in Pollen & Spores 4: 132. 1962), may be retained for a fossil-species of cysts even though cysts of the same kind are known to be part of the life cycle of the non-fossil species Pyrodinium bahamense L. Plate (in Arch. Protistenk. 7: 427. 1906).

Ex. 30. Reid (in Nova Hedwigia 29: 429–462. 1977) indicated that his new fossil-species Votadinium calvum was the resting cyst of the non-fossil dinoflagellate Peridinium oblongum (Auriv.) Cleve (in Kongl. Svenska Vetensk. Acad. Handl., n.s., 32(8): 20. 1900). Votadinium calvum can be used as the correct name for the cyst fossil-species because it has a fossil type and therefore does not compete for priority with P. oblongum.

11.8. Names of organisms (diatoms excepted) based on a non-fossil type are treated as having priority over names at the same rank based on a fossil type where these names are treated as synonyms for a non-fossil taxon.

Ex. 31. If Platycarya Siebold & Zucc. (in Abh. Math.-Phys. Cl. Königl. Bayer. Akad. Wiss. 3: 741. 1843), based on a non-fossil type, and Petrophiloides Bowerb. (Hist. Fruits London Clay: 43. 1840), based on a fossil type, are treated as heterotypic synonyms for a non-fossil genus, the name Platycarya is correct even though it is antedated by Petrophiloides.

Ex. 32. The generic name Metasequoia Miki (in Jap. J. Bot. 11: 261. 1941) was based on the fossil type of M. disticha (Heer) Miki. After discovery of the non-fossil species M. glyptostroboides Hu & W. C. Cheng, conservation of Metasequoia Hu & W. C. Cheng (in Bull. Fan Mem. Inst. Biol., Bot., ser. 2, 1: 154. 1948) as based on the non-fossil type was approved. Otherwise, any new generic name based on M. glyptostroboides would have been treated as having priority over Metasequoia Miki.

Ex. 33. Hyalodiscus Ehrenb. (in Ber. Bekanntm. Verh. Königl. Preuss. Akad. Wiss. Berlin 1845: 71. 1845), based on the fossil type of H. laevis Ehrenb. (l.c.: 78. 1845), is the name of a diatom genus that includes non-fossil species. If later synonymous generic names based on a non-fossil type exist, they are not treated as having priority over Hyalodiscus because Art. 11.8 excepts diatoms.

Ex. 34. Boalch & Guy-Ohlson (in Taxon 41: 529–531. 1992) synonymized the two non-diatom algal generic names Pachysphaera Ostenf. (in Knudsen & Ostenfeld, Iagtt. Overfladevand. Temp. Salth. Plankt. 1898: 52. 1899) and Tasmanites E. J. Newton (in Geol. Mag. 12: 341. 1875). Pachysphaera is based on a non-fossil type and Tasmanites on a fossil type. Under the Code in effect in 1992, Tasmanites had priority and was therefore adopted. Under the current Art. 11.8, which excepts only diatoms and not algae in general, Pachysphaera is the correct name for a non-fossil genus for which both of these names are treated as heterotypic synonyms.

Ex. 35. The non-fossil species Gonyaulax ellegaardiae K. N. Mertens & al. (in J. Phycol. 51: 563. 2015) was indicated in the protologue to produce a cyst corresponding to the fossil-species Spiniferites pachydermus (M. Rossignol) P. C. Reid (in Nova Hedwigia 25: 607. 1974). Both names were correct because Mertens & al. did not treat them as synonyms. However, if these names are treated as synonyms for the non-fossil species, G. ellegaardiae is treated as having priority even though it is antedated by S. pachydermus.

Note 5. In accordance with Art. 53, later homonyms are illegitimate whether the type is fossil or non-fossil.

Ex. 36. Endolepis Torr. (in Pacif. Railr. Rep. 12(2, 2): 47. 1860–1861), based on a non-fossil type, is an illegitimate later homonym of Endolepis Schleid. (in Schmid & Schleiden, Geognos. Verhältnisse Saalthales Jena: 72. 1846), based on a fossil type.

Ex. 37. Cornus paucinervis Hance (in J. Bot. 19: 216. 1881), based on a non-fossil type, is an illegitimate later homonym of C. paucinervis Heer (Fl. Tert. Helv. 3: 289. 1859), based on a fossil type.

Ex. 38. Ficus crassipes F. M. Bailey (Rep. Pl. Prelim. Gen. Rep. Bot. Meston’s Exped. Bellenden-Ker Range: 2. 1889), F. tiliifolia Baker (in J. Linn. Soc., Bot. 21: 443. 1885), and F. tremula Warb. (in Bot. Jahrb. Syst. 20: 171. 1894), each based on a non-fossil type, were illegitimate later homonyms of, respectively, F. crassipes (Heer) Heer (Fl. Foss. Arct. 6(2): 70. 1882), F. tiliifolia (A. Braun) Heer (Fl. Tert. Helv. 2: 68. 1856), and F. tremula Heer (in Abh. Schweiz. Paläontol. Ges. 1: 11. 1874), each based on a fossil type. The three names with non-fossil types have been conserved against their earlier homonyms in order to maintain their use (see App. IV).

11.9. For purposes of priority, names given to hybrids are subject to the same rules as are those of non-hybrid taxa at equivalent rank (but see Art. H.8).

Ex. 39. The name ×Solidaster H. R. Wehrh. (in Bonstedt, Pareys Blumengärtn. 2: 525. 1932) has priority over ×Asterago Everett (in Gard. Chron., ser. 3, 101: 6. 1937) for the hybrids between Aster L. and Solidago L.

Ex. 40. Anemone ×hybrida Paxton (in Paxton’s Mag. Bot. 15: 239. 1849) has priority over A. ×elegans Decne. (pro sp.) (Rev. Hort. (Paris) 1852: 41. 1852). The former is correct when both are considered to apply to the same hybrid, A. hupehensis (Lemoine & É. Lemoine) Lemoine & É. Lemoine × A. vitifolia Buch.-Ham. ex DC. (Art. H.4.1).

Ex. 41. Camus (in Bull. Mus. Natl. Hist. Nat. 33: 538. 1927) published the name ×Agroelymus E. G. Camus ex A. Camus without a description or diagnosis, mentioning only the names of the parent genera (Agropyron Gaertn. and Elymus L.). Because this name was not validly published under the Code then in force, Rousseau (in Mém. Jard. Bot. Montréal 29: 10–11. 1952) published a Latin diagnosis. However, under the present Code (Art. H.9), the date of valid publication of ×Agroelymus is 1927, not 1952, and therefore it has priority over the name ×Elymopyrum Cugnac (in Bull. Soc. Hist. Nat. Ardennes 33: 14. 1938).

11.10. The principle of priority does not apply above the rank of family (but see Rec. 16A).