Proposal to conserve the name Tweedia (Apocynaceae - Asclepiadoideae) with a conserved type

CALVIÑO, CAROLINA I.; FERNÁNDEZ, MARTINA; EZCURRA, CECILIA

TAXON

INT ASSOC PLANT TAXONOMY

Lugar: Viena; Año: 2014 vol. 63 p. 1375 - 1375

0040-0262

When Hooker & Arnott (J. Bot. 1: 291. 1834) originally described Tweedia, they validly published three species names, T. birostrata, T. brunonis and T. macrolepis, but they doubted if the second should be placed within Tweedia (?Tweedia? brunonis?This will probably be a distinct Genus??). Hooker & Arnott (J. Bot. 1: 291. 1834) did not indicate a type. Meyer (in Descole, Gen. & Sp. Plant. Argent. 2: 1-273. 1944) cited T. brunonis as type. However, we and others (John McNeill, pers. comm.) consider that T. brunonis cannot serve as type because it was not definitely included (see Art. 10.2; McNeill & al. in Regnum Veg. 154. 2012) in the original circumscription of Tweedia, the authors (Hooker & Arnott, J. Bot. 1: 291. 1834) having indicated that it probably belonged in a separate genus. Others (Fred Barrie, Gerry Moore, pers. comm.), however, conclude that T. brunonis was definitely included (definite inclusion being effected by citation of a validly published species name; see Art. 10.3) in the original circumscription of Tweedia (and, therefore, able to serve as type), the original authors? (Hooker & Arnott, J. Bot. 1: 291. 1834) supposition of T. brunonis not being in Tweedia being based on a hypothetical splitting of Tweedia. Later Bullock (Kew Bull. 13: 97?100. 1958) selected Tweedia macrolepis as type of the genus name because it was the only species collected by John Tweedie. Rua (Parodiana 5: 375?410. 1989) rejected the typification by Bullock (Kew Bull. 13: 97?100. 1958) on the grounds that it had been selected by a mechanical method (contrary to Art. 10.5(b); McNeill & al. in Regnum Veg. 154. 2012) and selected T. birostrata as the type of Tweedia. We agree with Rua?s (Parodiana 5: 375?410. 1989) conclusion and further point out that Rec. 9A.2 of the Code (McNeill & al. in Regnum Veg. 154. 2012) regarding lectotypification of species and infraspecific names gives as an example of mechanical method ?the automatic selection ? of a specimen collected by the person after whom a species is named?, a method similar to Bullock?s (Kew Bull. 13: 97?100. 1958). Others (Fred Barrie, John McNeill, pers. comm.) disagree and would not regard Bullock?s (Kew Bull. 13: 97?100. 1958) method of selection as mechanical. Tweedia macrolepis was transferred to Oxypetalum by Decaisne (in Prodr. 8:585. 1844) soon after its original description, and never again treated within Tweedia. If Bullock´s (Kew Bull. 13: 97?100. 1958) selection of the type of Tweedia is not considered against the ICN rules (e.g. following Barrie & McNeill´s interpretation of what a mechanical method of selection is) then the name Tweedia will be synonymized under Oxypetalum, and the seven species until now treated within Tweedia would need to be transferred to Turrigera Decne., resulting in the creation of six new combinations. Turrigera has been treated under the synonymy of Tweedia since 1904 (Malme, Ark. Bot. 2: 1?18. 1904) and never used again in any scientific publication. On the contrary, all publications (more than 15) since this year have used the name Tweedia for this group of Asclepiadoideae species from southwestern South America (see Calviño et al., this issue), the most important being: Malme, Ark. Bot. 2: 1?18. 1904; Meyer in Descole, Gen. & Sp. Plant. Argent. 2: 1-273. 1944; Marticorena & Quezada, Gayana Bot. 42: 1?157. 1985; Rua, Parodiana 5: 375?410. 1989; Ezcurra in Zuloaga et al., Cat. Plant. Vasc. Argent. 2: 78?98. 1999, and in Correa, Fl. Patag. 6: 58?77. 1999; Liede-Schumann et al., Syst. Bot. 30: 184?195. 2005; Ezcurra et al., Cat. Plant. Vasc. Cono Sur 2: 1090?1143. 2008; Rapini et al., Phytotaxa 26: 9?16. 2011. In summary, we reject Meyer?s (in Descole, Gen. & Sp. Plant. Argent. 2: 1-273. 1944) selection of Tweedia brunonis and Bullock?s (Kew Bull. 13: 97?100. 1958) selection of T. macrolepis and accept Rua?s (Parodiana 5: 375?410. 1989) selection of T. birostrata as the type of Tweedia. However, we acknowledge that others would accept either Meyer?s (in Descole, Gen. & Sp. Plant. Argent. 2: 1-273. 1944) or Bullock?s (Kew Bull. 13: 97?100. 1958) typification, thus rendering Rua?s (Parodiana 5: 375?410. 1989) typification superfluous, and compromising the stability of the nomenclature of the group. Because the typification of Tweedia is rooted in divergent but defensible interpretations of the ICN, resolution of this particular case seems only possible by means of conservation of the name Tweedia with the conserved type of T. birostrata under Art. 14 of the ICN (McNeill & al. in Regnum Veg. 154. 2012). This, will preserve the current usage of the name and avoid disadvantageous nomenclatural changes.