11.1. Each family or taxon of lower rank with a particular circumscription, position, and rank can bear only one correct name, special exceptions being made for 9 families and 1 subfamily for which alternative names are permitted (see Art. 18.5 and 19.7). However, the use of separate names for the form-taxa of fungi and for form-genera of fossil plants is allowed under Art. 3.3 and 59.5.
11.2. In no case does a name have priority outside the rank in which it is published (but see Art. 53.5).
Ex. 1. Campanula sect. Campanopsis R. Br. (Prodr.: 561. 1810) when treated as a genus is called Wahlenbergia Roth (1821), a name conserved against the taxonomic synonym Cervicina Delile (1813), and not Campanopsis (R. Br.) Kuntze (1891).
Ex. 2. Magnolia virginiana var. foetida L. (1753) when raised to specific rank is called M. grandiflora L. (1759), not M. foetida (L.) Sarg. (1889).
Ex. 3. Lythrum intermedium Ledeb. (1822) when treated as a variety of L. salicaria L. (1753) is called L. salicaria var. glabrum Ledeb. (Fl. Ross. 2: 127. 1843), not L. salicaria var. intermedium (Ledeb.) Koehne (in Bot. Jahrb. Syst. 1: 327. 1881).
Ex. 4. When the two varieties constituting Hemerocallis lilioasphodelus L. (1753), var. flava L. and var. fulva L., are considered to be distinct species, the one not including the lectotype of the species name is called H. fulva (L.) L. (1762), but the other one bears the name H. lilioasphodelus L., which in the rank of species has priority over H. flava (L.) L. (1762).
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 (see Art. 14) or where Art. 11.7, 15, 19.4, 56, 57, or 59 apply.
Ex. 5. When Aesculus L. (1753), Pavia Mill. (1754), Macrothyrsus Spach (1834) and Calothyrsus Spach (1834) are referred to a single genus, its name is Aesculus L.
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 in 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, 15, 56 or 57, or (b) if the resulting combination would be invalid under Art. 32.1(b) or illegitimate under Art. 53, or (c) if Art. 11.7, 22.1, 26.1, or 59 rule that a different combination is to be used.
Ex. 6. 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 substitute name D. sect. Ariadna Wendelbo (in Bot. Not. 112: 496. 1959) is illegitimate.
Ex. 7. Antirrhinum spurium L. (1753) when transferred to Linaria Mill. is called L. spuria (L.) Mill. (1768).
Ex. 8. When transferring Serratula chamaepeuce L. (1753) to Ptilostemon Cass., Cassini illegitimately named the species P. muticus Cass. (1826). In that genus, the correct name is P. chamaepeuce (L.) Less. (1832).
Ex. 9. Spartium biflorum Desf. (1798) when transferred to Cytisus Desf. could not be called C. biflorus because of the previously and validly published C. biflorus L'Hér. (1791); the substitute name C. fontanesii Spach (1849) was therefore correctly proposed.
Ex. 10. Spergula stricta Sw. (1799) when transferred to Arenaria L. is called A. uliginosa Schleich. ex Schltdl. (1808) because of the existence of the name A. stricta Michx. (1803), based on a different type; but on further transfer to the genus Minuartia the epithet stricta is again available and the species is called M. stricta (Sw.) Hiern (1899).
Ex. 11. Arum dracunculus L. (1753) when transferred to Dracunculus Mill. is named D. vulgaris Schott (1832), as use of the Linnaean epithet would result in a tautonym.
Ex. 12. Cucubalus behen L. (1753) when transferred to Behen Moench was legitimately renamed B. vulgaris Moench (1794) to avoid the tautonym "B. behen". In Silene L., the epithet behen is unavailable because of the existence of S. behen L. (1753). Therefore, the substitute name S. cucubalus Wibel (1799) was proposed. This, however, is illegitimate since the specific epithet vulgaris was available. In Silene, the correct name of the species is S. vulgaris (Moench) Garcke (1869).
Ex. 13. 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. 14: 115. 1903).
11.5. When, for any taxon of the rank of family or below, a choice is possible between legitimate names of equal priority in the corresponding rank, or between available final epithets of names of equal priority in the corresponding rank, the first such choice to be effectively published (Art. 29, 30, 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).
Note 1. 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 nomenclatural synonyms thereof.
Ex. 14. When Dentaria L. (1753) and Cardamine L. (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. 15. When Entoloma (Fr. ex Rabenh.) P. Kumm. (1871), Leptonia (Fr. : Fr.) P. Kumm. (1871), Eccilia (Fr. : Fr.) P. Kumm. (1871), Nolanea (Fr. : Fr.) P. Kumm. (1871), and Claudopus Gillet (1876) are united, one of the generic names simultaneously published by Kummer must be used for the combined genus. Donk, who did so (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. 16. Brown (in Tuckey, Narr. Exp. Congo: 484. 1818) was the first to unite Waltheria americana L. (1753) and W. indica L. (1753). He adopted the name W. indica for the combined species, and this name is accordingly treated as having priority over W. americana.
Ex. 17. Baillon (in Adansonia 3: 162. 1863), when uniting for the first time Sclerocroton integerrimus Hochst. (1845) and S. reticulatus Hochst. (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, Excoecaria, Sapium) to which the species is assigned.
Ex. 18. Linnaeus (1753) simultaneously published the names Verbesina alba and V. prostrata. Later (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. 3: 438. 1832), who adopted the name E. prostrata (L.) L. Therefore V. prostrata is treated as having priority over V. alba.
Ex. 19. Donia speciosa and D. formosa, which were simultaneously published by Don (1832), were illegitimately renamed Clianthus oxleyi and C. dampieri by Lindley (1835). Brown (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. C. speciosus (D. Don) Asch. & Graebn. (1909), published with D. speciosa and C. dampieri listed as synonyms, is an illegitimate later homonym of C. speciosus (Endl.) Steud. (1840); again, conditions for a choice under Art. 11.5 were not satisfied. Ford & Vickery (1950) published the legitimate combination C. formosus (D. Don) Ford & Vickery and cited D. formosa and D. speciosa as synonyms, but since the epithet of the latter was unavailable in Clianthus a choice was not possible and again Art. 11.5 does not apply. Thompson (1990) was the first to effect an acceptable choice when publishing the combination Swainsona formosa (D. 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 or names of the same date and rank that established it.
Note 2. 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. 20. Heracleum sibiricum L. (1753) includes H. sibiricum subsp. lecokii (Godr. & Gren.) Nyman (Consp. Fl. Europ.: 290. 1879) and H. sibiricum subsp. sibiricum automatically established at the same time. When H. sibiricum is included in H. sphondylium L. (1753) as a subspecies, the correct name for the taxon is H. sphondylium subsp. sibiricum (L.) Simonk. (Enum. Fl. Transsilv.: 266. 1887), not subsp. lecokii, whether or not subsp. lecokii is treated as distinct.
Ex. 21. The publication of Salix tristis var. microphylla Andersson (Salices Bor.-Amer.: 21. 1858) created the autonym S. tristis Aiton (1789) var. tristis. If S. tristis, including var. microphylla, is recognized as a variety of S. humilis Marshall (1785), the correct name is S. humilis var. tristis (Aiton) Griggs (in Proc. Ohio Acad. Sci. 4: 301. 1905). However, if both 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 both used.
Ex. 22. In the classification adopted by Rollins and Shaw, Lesquerella lasiocarpa (Hook. ex A. Gray) S. Watson (1888) is composed of two subspecies, subsp. lasiocarpa (which includes the type of the name of the species and is cited without an author) and subsp. berlandieri (A. Gray) Rollins & E. A. Shaw. The latter subspecies is composed of two varieties. In that classification the correct name of the variety which includes the type of subsp. berlandieri is L. lasiocarpa var. berlandieri (A. Gray) Payson (1922), not L. lasiocarpa var. berlandieri (cited without an author) or L. lasiocarpa var. hispida (S. Watson) Rollins & E. A. Shaw (1972), based on Synthlipsis berlandieri var. hispida S. Watson (1882), since publication of the latter name established the autonym S. berlandieri A. Gray var. berlandieri which, at varietal rank, is treated as having priority over var. hispida.
11.7. Names of plants (algae excepted) based on a non-fossil type are treated as having priority over names of the same rank based on a fossil (or subfossil) type.
Ex. 23. If Platycarya Siebold & Zucc. (1843), a non-fossil genus, and Petrophiloides Bowerb. (1840), a fossil genus, are united, the name Platycarya is accepted for the combined genus, although it is antedated by Petrophiloides.
Ex. 24. The generic name Metasequoia Miki (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 (1948) as based on the non-fossil type was approved. Otherwise, any new generic name based on M. glyptostroboides would have had to be treated as having priority over Metasequoia Miki.
11.8. For purposes of priority, names in Latin form given to hybrids are sub-ject to the same rules as are those of non-hybrid taxa of equivalent rank.
Ex. 25. The name xSolidaster H. R. Wehrh. (1932) antedates the name xAsterago Everett (1937) for the hybrid Aster L. x Solidago L.
Ex. 26. The name xGaulnettya Marchant (1937) antedates the name xGaulthettya Camp (1939) for the hybrid Gaultheria L. x Pernettya Gaudich.
Ex. 27. Anemone xhybrida Paxton (1848) antedates A. xelegans Decne. (1852), pro sp., as the binomial for the hybrids derived from A. hupehensis (Lemoine & E. Lemoine) Lemoine & E. Lemoine x A. vitifolia Buch.-Ham. ex DC.
Ex. 28. Camus (in Bull. Mus. Natl. Hist. Nat. 33: 538. 1927) published the name xAgroelymus A. Camus as the name of a nothogenus, without a Latin description or diagnosis, mentioning only the names of the parents involved (Agropyron Gaertn. and Elymus L.). Since this name was not validly published under the Code then in force (Stockholm 1953), Rousseau (in Mém. Jard. Bot. Montréal 29: 10-11. 1952), published a Latin diagnosis. However, the date of valid publication of the name xAgro-elymus under this Code (Art. H.9) is 1927, not 1952, and the name also antedates xElymopyrum Cugnac (in Bull. Soc. Hist. Nat. Ardennes 33: 14. 1938) which is accompanied by a statement of parentage and a description in French but not Latin.
11.9. The principle of priority is not mandatory for names
of taxa above the rank of family (but see Rec. 16B).