Oxalis eriocarpa De Candolle (1825: 23)

Nuernberg-Silva, Anelise & Fiaschi, Pedro, 2021, Taxonomic revision and morphological delimitation of Oxalis sect. Ripariae (Oxalidaceae), Phytotaxa 529 (1), pp. 125-159 : 137-138

3. Oxalis eriocarpa De Candolle (1825: 23)

≡ Trifolium magellanicum Poiret (1808: 25) non Oxalis magellanica Forster (1789: 33). Type (lectotype designated by Lourteig (1983: 73):— URUGUAY. Montevideo, May 1767, Commerson 84 (P00295091; isolectotypes: FI006256 [web]!, P00678569!, P02440081!, P02440082!) (figs. 6, 8).

= Oxalis amara Saint-Hilaire (1825: 95) . Type (lectotype designated by Lourteig (1983: 73), first-step; second-step designated by López et al. (2018: 190):— BRAZIL. Rio Grande do Sul. Dans les paturages du Nbidi, 1816-21, A. Saint-Hilaire C² 1861 (P02440086! image of the lectotype available at https://science.mnhn.fr/institution/mnhn/collection/p/item/p02440086; isolectotypes: P02440084!, P02440085!).

= Oxalis amara var. monanthos Progel (1877: 492) . Type: Not designated.

= Oxalis amara var. scabra Progel (1877: 492) . Type: Not designated.

= Oxalis amara var. grandiflora R. Knuth (1930: 492) Type: Not designated: ≡ Oxalis uruguaycola Herter (1943: 211) . Type: Not designated.

Decumbent subshrub. Stem up to ca. 20 cm long, tuberose stem up to ca. 3 × 8 cm, lateral aerial branches prostrate; shorter hairs 0.1–0.2 mm long, patent or curved, sparse to abundant; longer hairs 0.5–2 mm long, ascending, patent and descending, abundant, yellowish; glandular hairs ca. 0.5 mm long, occasional throughout; internodes 1–2.1 cm long. Stipules ca. 2 × 1 mm, rectangular, connate to the petiole, hairs ca. 1 mm long; petiole ca. 1–5 cm long, pulvina ca. 0.2 mm long. Leaf blades 9–25 × 9–26 mm, coriaceous, widely depressed obovate to very widely obovate, slightly discolorous, the base cuneate, the apex retuse to obcordate; shorter hairs ca. 1 mm long, appressed, sparse adaxially, moderate abaxially; longer hairs ca. 2 mm long, appressed, moderate in both surfaces; glandular hairs ca. 1 mm long, occasional abaxially. Dichasia with up to 4 flowers, as long as the leaves; peduncle 0.5–2 cm long; hairs as in stem; glandular hairs moderate; bracts ca. 1.5 × 2 mm, lanceolate, hairs ca. 3 mm long; bracteoles ca. 2 × 0.5 mm, lanceolate. Pedicels 1–10 mm long; sepals 3–6 × 0.8–1.2 mm, base rounded, apex acute, hairs ca. 1 mm long, simple and glandular, moderate, ascending; petals yellow, 11–23 mm long, spatulate, the apex crenate-denticulate, occasionally reddish, adaxially with glandular hairs sparse to moderate; shorter stamens ca. 4 mm long, glabrous, longer ca. 6 mm long, hairs ascending; pistil ca. 10 mm long, hairs ascending, abundant, stigmas papillose. Capsules 4 × 8 mm, depressed ovoid, 5-lobed, hairs ca. 2 mm long, patent, abundant, rigid. Seeds 1 per locule, 2.6–3.8 × 1.7–2.5 mm, elliptic, the base rounded, the apex acute.

Distribution and habitat: —This species is associated to the Pampas biome at Argentina, Brazil, and Uruguay, with occasional occurrences in seasonally dry forests (Atlantic Forest biome) at western Rio Grande do sul state in Brazil (fig. 6). Its distribuition is sparse in open areas, such as grasslands, ravines or among rocks at full sun. Populations of Oxalis eriocarpa are commonly observed in grasslands after burning, due to resprouting from underground stems.

Phenology: —Flowers and fruits have been collected from August to January.

Conservation status: — Oxalis eriocarpa is widespread in Rio Grande do Sul state, northeastern Argentina and Uruguay (EOO = 383,989 km ²), however its distribution is discontinuous, and the populations comprise in total an Area of Occupancy of ca. 220 km ². Despite its resilience to fire, this species does not tolerate long shading periods or intensive soil conversion for agriculture. Few areas of the Pampa biome area protected ( Overbeck et al. 2015), and there is a single record of this species in a protected area (Saint-Hilaire Municipal Natural Park, Rio Grande do Sul, Brazil). Because the habitat where O. eriocarpa grows has good connectivity, we propose a conservative status of Near Threatened (NT).

Typification of Trifolium magellanicum : —In the protologue, Poiret annotated: “ croit au détroit de Magellan, où elle eté decouverte par Commerson (V.S. in herb. LAM) ”, indicating that he analyzed a dried specimen collected by Commerson, probably in the Magellan Strait. Lourteig (1983) indicated the specimen at P-LAM as the lectotype (P00295091); additional samples at P-Jussieu, and in the general collection of P and FI are thus isolectotypes. Poiret recognized the fact that the material did not fit properly in Trifolium L. Afterwards, Candolle (1825) placed the species in Oxalis and commented that label information point to Montevideo as the type locality, not “Magellan”.

Taxonomic notes: — Oxalis eriocarpa can be easily recognized among the other species of the section by leaflets with the apex retuse to obcordate, and because they are entirely covered by long and stiff hairs ca. 2 mm long. It is also the species of the section with the largest flowers (up to ca. 23 mm long) with vivid yellow corolla, reddish on nectar guides and, sometimes, petals margins (figs. 8b-c).

Specimens examined: — ARGENTINA. Corrientes: Ituizaingó, Rincón Ombú Chico, 17 November 1978, M. M . Arbo et al. 2102 ( CTES); 15 km E de ruta nacional nº 12, estrada a San Carlos , 13 November 1971, A . Krapovickas et al. 17996 ( CTES); Predio Santo Domingo , 20 May 2008, H. A . Keller et al. 5522 ( CTES); 20 km W de San Carlos , 9 September 1974, C. L . Cristóbal & A . Krapovickas 1726 ( CTES); Paso de los libres, Laguna Mansa , 21 September 1974, A . Schinini et al. 7229 ( CTES); 3 cerros, Co. de Susini , 16 September 1974, A . Schinini et al. 18539 ( CTES, MBM); Santo Tomé, Estancia Garruchos , 13 November, E. R . Guaglianone 97 ( SI); Ruta 40, 8 km NE de Santo Tome , 29 July 1974, M . Dematteis et al. 714 ( CTES); Ayo. Chimiray , 23 September 1974, A . Krapovickas et al. 26137 ( CTES); Garruchos , 9 October 1974, A . Schinini & O . Ahumada 20760 ( CTES); Colonia Garabi , 21 September 1974, A . Krapovickas et al. 25964 ( CTES); 31 October 1974, A . Krapovickas & C. L . Cristóbal 16408 ( CTES) . Entre Rios: Concordia, De San Salvador a Concordia, 18 October 1974, N. S . Troncoso et al. 1984 ( CTES). Misiones: Apostoles, Cruce rutas 201-203, 30 km NE de Apóstoles , 22 September 1974, A . Krapovickas et al. 15461 ( CTES); Candelaria , Santa Ana, 14 September 1912, F. M . Rodríguez 586 ( SI); Posadas , 15 September 1912, C . Schrottky 203 ( SI); Leandro N . Alem, Ruta 14, General Güemes, 22 October, A. L. Cabrera 29329 ( SI); Santa Ana , 1 November 1974, M . Crovetto 9682 ( CTES) . BRAZIL. Rio Grande do Sul: Júlio de Castilhos , 28 October 2016, A . Nuernberg et al. 1830 ( FLOR); Pelotas, 26 August 1974, J. S. C . Sacco 228 ( CTES, P); Pinheiro Machado, Cox. Pedras Altas , 11 November 1974, T. M . Pedersen 11441 ( CTES, P); Santo Angelo, Granja Piratini , 23 September 1974, K . Hagelund. 10485 ( CTES); São Francisco de Assis , 28 October 2016, A . Nuernberg et al. 1824 ( FLOR); São Gabriel , BR290 , some 20 km E of Rosário do Sul, 9 November 1974, T. M . Pedersen 11408 ( CTES, P); Viamão, Parque Saint-Hilaire , A . Nuernberg 1820 ( FLOR) . URUGUAY. Maldonado: Ruta 60, km 37, 14 November 1974, J. M . Bonifacio et al. 1820 ( CTES) ; Rivera, Ayo. Curticera, Ruta 5, km 491, 30°58’45’’S, 55°34’31’’W, 12 December 1997, S . Neffa et al. 464 ( CTES) ; Tacuarembó, Camino a Gruta de los Cuervos, esculea “Capón de la Yerba”, 31°36’50’’S, 56°03’17’’W, 214 msm, 17 November 2007, S. Neffa 2068 ( CTES) .