Oxalis pampeana Nuernberg-Silva & Fiaschi

Nuernberg-Silva, Anelise & Fiaschi, Pedro, 2021, Taxonomic revision and morphological delimitation of Oxalis sect. Ripariae (Oxalidaceae), Phytotaxa 529 (1), pp. 125-159 : 145-147

7. Oxalis pampeana Nuernberg-Silva & Fiaschi , nom. & stat. nov.

pro O. bifrons subsp. littoralis Lourteig (1983: 42) , non O. littoralis Eckl. & Zeyh. (1835: 90) nec O. littoralis Pohl ex Progel (1877: 501) . Type (lectotype designated by Lourteig 1983: 42, first-step; second-step designated here):— BRAZIL. Rio Grande do Sul, 2 October 1975, N.I. Matzenbacher 230 (P02440126!, image of the lectotype available at https://plants.jstor.org/stable/viewer/10.5555/ al.ap.specimen.p02440126?loggedin=true, isolectotypes MO2476022 [web]!, P02440127!,P02440128!,P02440129!, V0066501F [web]!).(figs. 12, 13).

Stoloniferous herb. Stem slender, up to ca. 60 cm tall, reddish; shorter hairs ca. 0.1 mm long, patent, sometimes curved, thin, moderate to very abundant; longer hairs 0.5–1 (1.5) mm long, ascending, patent and descending, sparse to moderate, abundant in young parts; glandular hairs ca. 0.5 mm long, sparse to moderate; internodes 0.2–8.8 cm long, alternating between very short internodes and long internodes, nodes radicant. Stipules 1–4.5 × 1.5–3 mm, semicircular, connate to the petiole, hairs 1–1.5 mm long, sparse to moderate; petioles 3–26 cm long; shorter hairs 0.1–0.2 mm long, curved, occasional to moderate (abundant in specimens from grasslands); longer hairs 1–2 mm long, ascending, patent and descending, moderate to very abundant, especially in the young parts; glandular hairs ca. 0.5 mm long, occasional to moderate; pulvina ca. 1 mm long, hairs 1–2 mm long, patent, abundant. Leaf blades 1.1–3.7 × 0.6– 2.9 cm, coriaceous, widely obovate to obovate, discolorous, the base cuneate, the apex obtuse to rounded, eventually retuse, sometimes acute in young leaves; shorter hairs ca. 0.3 mm long, appressed, occasional to sparse; longer hairs 1–1.5 mm long, appressed and ascending, occasional to moderate along veins, moderate to abundant throughout; glandular hairs ca. 0.5 mm, absent or sparse adaxially; longer hairs 1–2 mm long, appressed, very abundant throughout abaxially. Dichasia with up to 5 flowers, shorter than the leaves; peduncle 0.5–3.2 cm long, shorter hairs 0.1–0.2 mm long, curved or appressed, ascending and descending, abundant; longer hairs 0.5–1 mm long, patent, ascending or descending, moderate to abundant; glandular hairs ca. 0.5 mm long, sparse to moderate; bracts 1–1.5 × 0.5 mm, lanceolate; bracteoles 0.5–1 × 0.5 mm, lanceolate. Pedicels 2–11 mm long; sepals 2.6–4 × 0.75–1.5 mm, base rounded, apex acute, shorter hairs ca. 0.3 mm long, moderate, longer hairs 0.5–1 mm long, appressed to ascending, moderate to abundant, sometimes concentrate in the margin, glandular hairs ca. 0.5 mm, sparse; petals yellow, 9–12 mm long, spatulate, the apex crenate-denticulate, adaxially with glandular hairs, moderate; shorter stamens ca. 3 mm long, glabrous, longer hairs ca. 5 mm long, with hairs ascending; pistil ca. 6 mm long, hairs ascending, abundant, stigmas papillose. Capsules 2.4 (4.1)–4 (6.3) × 2.1 mm, depressed ovoid, 5-lobed, hairs ca. 0.5 mm long, ascending, moderate. Seeds 1 per locule, ca. 3 × 2.2 mm, widely elliptic to elliptic, the base rounded, the apex acute.

Distribution and habitat: —This species is endemic to Rio Grande do Sul state, where it is commonly found along the central-northern coast in butiazais, a vegetation type on sandy soils with Butia spp. (Arecaceae) , but also at nearby localities (e.g., Depressão Central, Serra do Sudeste), and with a disjunct record at Santiago, in the western part of the state, which is characterized by grasslands on shallow sandy soils.

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

Etymology: The name of this species refers to the Pampa biome, where the species occurs ( IBGE 2019).

Conservation status: — Oxalis pampeana was collected at seven different localities, but it has never been recorded at any protected area, and the places where it is found are mostly degraded due to urban expansion at coastal areas and agricultural activities. Its AOO is 28 km ², with an infered decline in the area extent and habitat quality, so we recommend its classification as endangered [EN B2a,b(iii)].

Nomenclatural notes: — There are four sheetes of “ N. I. Matzenbacher 230 ” at P, and according to the Art. 9.17 of ICN, a second-step lectotypification may be necessary. We selected P02440126 as the second-step lectotype because it fits unambiguously the description of the protologue, and bears more leaves and more clearly visible inflorescences compared to the isolectotypes .

Taxonomic comments: — Oxalis pampeana is similar to O. bifrons , from which it can be distinguished by widely obovate to obovate (vs. widely depressed obovate to very widely obovate leaflets), with the abaxial blade surface entirely covered by hard appressed and very abundant hairs 1–2 mm long (vs. with curved, ascending or patent abundant hairs 0.1–0.2 mm long, and appressed, moderate to abundant longer hairs 1–2 mm long not entirely covering the blade abaxial surface). Moreover, the inflorescences of Oxalis pampeana are up to 5-flowered (vs. up to 13-flowered in O. bifrons ), and their geographic distributions do not overlap (figs. 6, 12).

Specimens examined: — BRAZIL. Rio Grande do Sul: Arroio dos Ratos, Granja Faxinal, 23 August 1975, K. Hagelund 9216 ( P); K . Hagelund 9220 ( P); Fazenda Faxinal , 14 October 1979, K . Hagelund 13099 ( ICN); 29 August 1981, D. B . Falkenberg 236 ( FLOR); 24 August 1985, F. A . Silva-Filho 478 ( FLOR); Cidreira, Fazenda Azaléia, próximo à Lagoa Manuel Nunes , 19 July 2012, E . Valduga 478 ( HUCS [photo]) ; Encruzilhada do Sul, 13 Km N do Rio Camaquã no Passo dos Marinheiros, B. Irgang et al. s.n. ( ICN 20633); Osório, Fazenda do Arroio para Osório, September 1957, B . Rambo 61463 ( P) ; Palmares do Sul, 1 October 2010, I . Boldrini 1688 ( ICN); Santiago, de Santiago para Florida, 2 October 2011, A. A . Schneider 1751 ( ICN); Torres , 25 September 1969, J . Favalli et al. s.n. ( ICN7043 ); Butiazal atrás do posto Esso, próximo da BR 101 e do posto da Polícia Rodoviária Federal, 27 October 1981, D. B . Falkenberg 205 ( FLOR); butiazal, 4 February 1984, K . Hagelund s.n. ( ICN106819 ); 29°21’12.5’’S, 49°47’23.3’’W , 6 November 2016, A . Nuernberg et al. 1875 ( FLOR) .