Oxalis bifrons Progel (1877: 495)

Nuernberg-Silva, Anelise & Fiaschi, Pedro, 2021, Taxonomic revision and morphological delimitation of Oxalis sect. Ripariae (Oxalidaceae), Phytotaxa 529 (1), pp. 125-159 : 135-136

2. Oxalis bifrons Progel (1877: 495) . Type (lectotype designated by Lourteig 1983: 39):—[Icon] Tab CV, Fig. 2 in Progel (1877) (figs. 6–7).

Stoloniferous herb. Stem slender, up to ca. 60 cm long (150 cm in literature), reddish; shorter hairs ca. 0.1 mm long, patent, very thin, moderate to abundant; longer hairs 0.5–1(1.5) mm long, ascending, patent and descending, sparse to moderate (very abundant on young parts); sparse glandular hairs ca. 0.5 mm long; internodes 0.1–8.5 cm long, alternating between very short and long internodes, nodes rooting. Stipules 3–5 × 2–3 mm, semicircular, the apex connate to the petiole, hairs like on stem; petioles 4–12 cm long, pulvina ca. 1 mm long, hairs 1–2 mm long, patent, abundant. Leaf blades 0.8–3.8 × 0.8–2.7 cm, coriaceous, widely depressed obovate to very widely obovate, rarely widely obovate, discolorous, with the base cuneate, the margin entire, with abundant, ascending hairs ca. 1 mm long; with the apex obtuse to rounded, or retuse; shorter hairs ca. 0.2 mm long, curved or appressed to ascending, sparse to moderate adaxially, abundant abaxially; longer hairs ca. 1–2 mm long, appressed, sparse to moderate adaxially, moderate to abundant abaxially; glandular hairs ca. 0.5 mm, sparse abaxially. Dichasia with 13 flowers, as short as the leaves; peduncle 0.5–4.7 cm long; shorter hairs 0.1–0.2 mm long, appressed to ascending and descending, abundant, sometimes curved; longer hairs 1–2.5 mm long, patent, moderate to abundant; glandular hairs ca. 1 mm long, occasional; bracts 1–2.5 × 0.2–0.5 mm, lanceolate; bracteoles 0.5–1 × 0.2 mm, lanceolate. Pedicels 0.3–2 mm long; sepals 3–4 × 1 mm, base rounded, apex acute, shorter hairs ca. 0.2 mm long, moderate, longer hairs 0.5–1 mm long, appressed to ascending, moderate, glandular hairs ca. 0.5 mm long, occasional; petals yellow, 6–10 mm long, spatulate, crenate-denticulate at the apex, adaxially with sparse glandular hairs; shorter stamens ca. 3 mm long, glabrous, longer ca. 5 mm long, hairs ascending; pistil ca. 6 mm long, hairs ascending, abundant, stigmas papillose. Capsules 3–6 × 3–4 mm, very widely ovoid, 5-lobed, hairs ca. 0.5 mm long, ascending, moderate. Seeds 1 per locule, 1.6–3.2 × 1–1.9 mm, elliptic, with rounded base and acute apex.

Distribution and habitat: —This species has been collected in Brazil (Paraná state) and Argentina (Missiones province), always in shady habitats within forests or forest edges.

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

Conservation status: — Oxalis bifrons is known from four localities at western Paraná state ( Brazil) and the Missiones province in Argentina. It is associated to Araucaria forests, which have been historically explored for logging and remains with less than 1% of its original cover in good conservation status. This species has not been recorded in protected areas and its sampling spots are immersed within and extensive agricultural matrix. Due to its EOO = 7,382 km ² and AOO = 16 km ², with an inferred decline in area extent and habitat quality due to advance of agricultural activities and urbanization, we recommend to categorize it as Endangered [EN B2a,b(iii)].

Nomenclatural notes: — Oxalis bifrons was described by Progel (1877: 495) based on a Sellow’s collection. Lourteig (1983, 2000) suggested that this sample was deposited at B and that it was presumably destroyed during World War II ( Hiepko 1987). This specimen was considered to be collected at Montevideo ( Uruguay) by Progel (l.c.), but it is very likely that this locality was wrongly attributed, as there are no other samples of this species from Uruguay. Argentinean samples are rare. We agree with Lourteig (1983, 2000) that this collection is likely from Brazil, without precise locality indication.

Taxonomic notes: — Oxalis bifrons differs from O. sarmentosa mostly by the rounded (vs. acute) leaflet apex, and the blade wider above (vs. below) the mid portion. The indumentum also differs, as in Oxalis bifrons leaflet abaxial surface bears more shorter and curved hairs 0.1–0.2 mm long and longer ones 1–2 mm long, while in O. sarmentosa leaf abaxial surface is glabrous or with shorter straight hairs 0.2–0.5 mm long and longer ones 1(–2) mm long. Oxalis bifrons is also similar to O. pampeana , from which it can be distinguished by leaflets with sparse to abundant hairs not covering the blades (vs. blades entirely covered by the indumentum). The two species are allopatric, as O. bifrons is restricted to western Paraná and northeastern Argentina, while O. pampeana occurs exclusively in Rio Grande do Sul coastal plains and (rarely) in the western part of the same state.

Specimens examined: — ARGENTINA. Missiones: San Pedro [as Gral. M. Belgrano], al sur de Bdo. de Irigoyen , 26°18’30,9’’S, 53°39’53,8’’W, 6 January 2011, H. A . Keller & M. M . Franco 9378 ( CTES); H. A . Keller & M. M . Franco 9411 ( CTES) ; BRAZIL. Paraná: Cantagalo, sítio Cachoeira , 17 September 2009, J. M . Silva et al. 7361 ( MBM, RB); Laranjeiras do Sul , 21 October 1969, G . Hatschbach 22581 ( CTES, MBM, NY00470357 [web], NY00470358 [web], P, UEC002860 [web]); Rincão Grande, 12 October 1974, G . Hatschbach 35209 ( MBM, P); Roncador, 19 December 1973, G . Hatschbach 32897 ( CTES, MBM, NY00470358 [web], P, RB 223184 [web], US 01853527 [web]).

Figures

FIGURE 2. Morphology of O. sect. Corniculatae. A–B: O. corniculata, A—fruiting branch (fruit, arrowhead),B—leaf insertions at stem, showing stipules (arrowhead); C–E: O. conorrhiza, C—habit, D—leaf adaxial surface, E—leaf insertions at stem, showing stipules; F–G: O. serpens, F—habit, G—flowering branch; H–J: O. subvillosa, H—habit, I—inflorescence, showing larger external sepals (arrowhead), J—leaf abaxial surface; K–L: O. tenerrima, K—habit, L—leaf insertions at stem, showing stipules (arrowhead). Photos: A–E, H, J–L. A. Nuernberg-Silva. F–G, I. P. Fiaschi.