Begonia unilateralis Rusby

Moonlight, Peter. W., Jara-Muñoz, Orlando A., Purvis, David A., Delves, Jay, Allen, Josh P. & Reynel, Carlos, 2023, The genus Begonia (Begoniaceae) in Peru, European Journal of Taxonomy 881, pp. 1-334 : 189-192

44. Begonia unilateralis Rusby

Figs 59B , 61

Phytologia 1 (2): 68 ( Rusby 1934).

– Type: BOLIVIA – [La Paz Department: Prov. Sud Yungas] • Nequejahuira ; [16°20′ S, 67°50′ W]; 2435 m a.s.l.; 15–24 May 1926; G.H.H. Tate 657; lectotype: NY [ NY00118710 ], designated by Smith & Schubert (1944: 81).

Foster (1958: 138); Wasshausen et al. (2014: 386).

Begonia peltigera Irmsch., Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 76: 79 ( Irmscher 1953)

– Type: PERU – [Puno Region]: Prov. Sandia • 2100– 2300 m a.s.l.; [14°18′ S, 69°26′ W]; 13 Mar. 1902; A. Weberbauer 506; holotype: B [ B100243084 , B100243085 , 2 sheets]. Syn. nov.

Brako & Zarucchi (1993: 194); León & Monsalve (2006: 167).

Etymology

The epithet derives from the Latin for one (‘ ūnus ’) and sided (‘ laterālis ’). This probably refers to the leaf, which is much larger on one side of the midrib than the other.

Specimens examined

PERU – Puno Region: Prov. Sandia • ca 600 m south of Pilco; 14°17′11″ S, 69°10′06″ W; 1473 m a.s.l.; 8 Jan. 2021; B. Melchor 776ª; USM.

Description

Caulescent herb, to 100 cm high. Stem erect, branching; internodes to 12 cm long, to 6 mm thick, succulent, red, with a dense indumentum of lepidote scales, the scales circular to star-shaped. Stipules deciduous to late deciduous, lanceolate, 6–13 × 2–4 mm, apex acuminate, translucent, red, glabrous to sparsely lepidote scaled, margin entire, aciliate. Leaves> 5 per stem, alternate, basifixed; petiole 0.5–5.5 cm long, red, densely lepidote scaled; blade asymmetrical, transversely ovate, to 11 × 6.5 cm, succulent, apex obtuse to short acuminate, base short-cordate to cordate, basal lobes not overlapping, sinus to 10 mm deep, margin crenate to serrate, ciliate, upper surface green, glabrous to sparsely lepidote scaled, lower surface dull green, moderately to densely lepidote scaled, veins palmate-pinnate, 5–7 veined from the base, with 1–3 secondary veins on the larger side, 1–3 secondary veins on the smaller side. Inflorescences 1–3 per branch, bisexual, axillary, erect, cymose, with 2 branches, bearing up to 8 staminate flowers and 8 pistillate flowers, protandrous; peduncle to 3.5 cm long, red, with a dense indumentum of lepidote scales, bracts persistent, lanceolate to ovate, 3–6.5 × 1–3 mm, translucent, red, glabrous to lepidote scaled, apex attenuate to truncate, margin lacerate, ciliate. Staminate flowers: pedicels to 15 mm long, densely lepidote scaled; tepals 2, spreading, ovate, 8–14 × 8–12 mm, apex rounded, white to pink, glabrous lepidote scaled, margin entire to crenulate at the apex, aciliate; stamens 70–125, spreading, yellow, filaments 0.5–2 mm long, fused at the base onto a torus, anthers oblong, 1 × 0.75 mm, dehiscing via lateral slits, connectives extended to 0.5 mm, symmetrically basifixed. Pistillate flowers: pedicels to 28 mm long; bracteoles 2, positioned directly beneath the ovary, lanceolate to broadly ovate, 2.5–7 × 1.5–2 mm, apex acute to truncate, translucent, white to pink, lepidote scaled, margin lacerate, ciliate; tepals 5, rarely 6 (B. Melchor 776ª), subequal, deciduous in fruit, spreading, ellipsoid to lanceolate, 4–10 × 3.5–4 mm, apex acute, white to pink, sparsely lepidote scaled, margin entire to serrulate at the apex, ciliate; ovary body ovoid, 6–7 × 3–5.5 mm, white to pink, lepidote scaled, unequally 3-winged, wings triangular, largest 6–9 × 8–10 mm, smallest 6–8 × 2–4 mm; 3-locular, placentae branches divided, bearing ovules on both surfaces; styles 3, yellow, free, 3–5 mm long, irregularly 2-many times-divided, stigmatic papillae in spirally twisted bands. Fruiting pedicel to 30 mm long. Fruit body broadly ovoid, to 10 × 8 mm, drying brown, wings same shape as in ovary, the largest expanding to 13 × 12 mm, the smallest expanding to 10 × 4 mm.

Proposed conservation assessment

Known from a narrow elevational band either side of the Peru-Bolivia border and has a total EOO of ca 1800 km 2. Within the species range, its habitat is under pressure from small-scale subsistence farming and cocoa production. We were unable to locate B. unilateralis during fieldwork in September 2020 and it may be rare in Peru but appears locally common in Bolivia. We assess B. unilateralis as Endangered (EN B1ab(iii)), which replaces the assessment of B. peltigera as Data Deficient (DD) by León & Monsalve (2006).

Synonymy notes

Begonia peltigera was described as the only Andean species with an indumentum of peltate scales. This character is also found on the type collection of B. unilateralis , which was described 24 years earlier. The type of B. unilateralis has a much lower density of peltate scales than that of B. peltigera , but scale density seems to increase in this species closer to the Peruvian border. The only other character with which we can separate the types of B. unilateralis and B. peltigera is the depth of the sinus at the leaf base and we do not consider this sufficient to maintain the two species as separate.

Typification notes

The protologue of B. peltigera cites A. Weberbauer 506 in Berlin herbarium as type material ( Irmscher 1953: 79). There are two sheets of this collection in Berlin but as they are labelled as sheets ‘A’ (B100243084) and ‘B’ (B100243085) they are two sheets of the same collection and both part of the holotype.

Identification notes

Easily recognised as the only species of Peruvian Begonia with an indumentum of gold, peltate scales, reminiscent of those of Combretum ( Combretaceae ) species. The scales are often deciduous on herbarium specimens, which gives herbarium sheets a dandruff-like covering.

Distribution and ecology

Known from Peru and Bolivia. Within Peru, collected in Puno Region ( Fig. 59B ) in middle montane forest at an elevation of 1400–2440 m a.s.l.

Figures

Fig. 59. Distribution of Begonia sect. Hydristyles A.DC. in Peru and surrounding countries.A. B. andina Rusby (red). B. B. unilateralis Rusby (red). Black lines indicate country borders, grey lines indicate major administrative divisions, blue lines indicate rivers, and shading indicates elevation.

Fig. 61. Begonia unilateralis Rusby. A. Habit. B. Pistillate flower, front view. C. Staminate flowers, front view. All photographs taken by B. Melchor from B. Melchor 776ª in Sandia Province, Puno Region.