Opuntia rioplatense Font (2014: 85)

Köhler, Matias, Font, Fabián & Souza-Chies, Tatiana T., 2018, First record of Opuntia rioplatense (Cactaceae) for the Brazilian Flora, Phytotaxa 379 (4), pp. 293-296 : 293-295

Opuntia rioplatense Font (2014: 85) ( Fig. 1 ) nom. nov. pro Opuntia elata Salm-Dyck (1834: 361) var. obovata Walther

(1930: 204) non O. obovata Griffiths (1919: 202) .

Lectotype (designated by Crook & Mottram 1996: 140):—[Icon] Figure 1 in Walther (1930: 203).

Epitype (designated by Las Peñas et al. 2017: 113):— ARGENTINA. Santa Fe, Rosario, Zavalla, 33º01’27.89”S, 60º54’07.69”W, 10 November 2012, Galetti s.n. (UNR).

Distribution and habitat:— Opuntia rioplatense occurs in central and eastern Argentina (Buenos Aires, Córdoba, Corrientes, Entre Ríos, La Pampa and Santa Fe Provinces), central-western Uruguay (Paysandú, Soriano, Montevideo, Maldonado) and extreme southwestern Brazil (west of Rio Grande do Sul State, our new record). In Brazil, the species is apparently restricted to the Pampa biome, specifically in a steppic-savanna environment known as Espinilho Park. The Espinilho Park is characterized by the occurrence of Prosopis affinis Sprengel (1825: 326) , P. nigra ( Grisebach 1879: 118) Hieronymus (1881: 283) and Vachellia caven ( Molina 1782: 174) Seigler & Ebinger (2005: 148) , exhibiting similarities to the Chaco vegetation in Argentina, the largest South American seasonally dry forest, which is a mosaic of xerophytic forests, woodlands, shrubs, savannas and grasslands ( Roesch et al. 2009).

Notes on taxonomy, karyology and phylogeny: — Opuntia rioplatense is a taxon recently resurrected within Elata group species based on Opuntia elata var. obovata Walther ( Font 2014) , non O. obovata Griffiths (1919: 202) . O. rioplatense differs from O. elata because of its acute flower bud apex ( Fig. 1D ), obovate-elliptic cladodes ( Fig. 1C ) and the obovate fruits ( Fig. 1F ), in contrast to the obtuse-rounded bud apex, elongated-oblong cladodes and the shortly obpyriform fruits. O. rioplatense was already known by the end of the 19 th century by the first Argentine cactologists, but it was always erroneously cited as O. vulgaris Miller (1768) or O. paraguayensis Schuman (1899: 149) .

Opuntia rioplatense is reported as a tetraploid species (2 n = 4 x = 44) ( Realini et al. 2014a; Las Peñas et al. 2017), and our counts have reinforced that ploidy level (Köhler unpublished data). The phylogenetic position of O. rioplatense is still uncertain, as the only phylogeny of the sSA species cannot be considered as conclusive (see Realini et al. 2014b), although there is a clear distinct haplotype between O. elata , and O. rioplatense . The species is probably nested in the Elatae clade (see Majure et al. 2012), and further molecular data should provide for more robust phylogenetic hypothesis regarding the species of this clade (Köhler unpubl. data).

Notes on conservation status: —Although the species is widely distributed in Argentina and Uruguay, we emphasize its restricted occurrence in Brazil in a small area of the State of Rio Grande do Sul. Considering that to date, the species has not been cited or considered for the Brazilian flora ( Flora do Brasil 2018), we highlight the importance of investigating the state of conservation of the species in Brazilian territory to ensure its maintenance.

Figures

FIGURE 1. Opuntia rioplatense A. Habit (M. Köhler et al. 218) B. Trunk with spines (M. Köhler et al. 217) C. Details of cladodes (M. Köhler et al. 221) D. Floral bud with acute apex (M. Köhler et al. 221) E. Flowers in longitudinal section (M. Köhler et al. 220) F.Fruits with longitudinal section (M. Köhler et al. 221).