Begonia elachista Moonlight & Tebbitt

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 : 246-248

62. Begonia elachista Moonlight & Tebbitt

Figs 78A , 79

European Journal of Taxonomy 281: 5 ( Moonlight et al. 2017a).

– Type: PERU – Pasco Region: Prov. Oxapampa • Parque Nacional Yanachaga-Chemillén , Sector Paujil , 150 m from entrance to las cavernas on trail from Pauji; 10°20′40″ S, 75°16′01″ W; 432 m a.s.l.; 25 Feb. 2016; P.W. Moonlight & A. Daza 318; holotype: MOL; isotypes: E [ E00785221 ], MO [ MO-3237389 ], USM.

Etymology

Named for its status as the smallest known Begonia in the world, as the epithet derives from the Greek word ‘elachista’ meaning ‘least’.

Specimen examined

PERU – Pasco Region: Prov. Oxapampa • Dist. Palcazú, Parque Nacional Yanachaga-Chemillén , sector Paujil , Quebrada Túnel ; 10°20ʹ S, 75°15ʹ W; 429 m a.s.l.; 17 Mar. 2008; R. Vásquez, A. Monteagudo, I. Huamantupa & A. Peña 34030; E [ E00785220 ], HOXA, HUT, MO [ MO-2080521 ], USM.

Description

Caulescent, tuberous herb, to 3 cm high. Tuber sub-globose, 0.1–0.2 × 0.1–0.2 cm, with 1 growing point. Stem erect, branching; internodes to 0.75 cm long, to 0.1 mm thick, pale green, glabrous. Stipules persistent, narrowly-lanceolate, 0.5–1.5 × 0.2–0.5 mm, apex acuminate, aristate, translucent, pale green, glabrous, margin entire, ciliate. Leaves 1–4, alternate, basifixed; petiole 0.2–2.5 cm long, pale green, glabrous; blade symmetrical to subsymmetric, ovate to suborbicular, to 3 × 2.5 cm, membranaceous, apex obtuse, base cordate, basal lobes not overlapping sinus to 2 mm deep, margin irregularly crenate, ciliate, upper surface pale green, glabrous, lower surface very pale green, glabrous, veins palmate, 5–7 veined from the base. Inflorescences 1–2, bisexual, axillary, erect, a dichasial or monochasial cyme, with 1–2 branches, bearing up to 2 staminate flowers and 2 pistillate flowers, protandrous; peduncle to 4 cm long, pale green, glabrous, bracts persistent, elliptic, 1.5–2 × 0.1–0.3 mm, translucent, white, glabrous, apex acuminate, margin entire, ciliate. Staminate flowers: pedicels to 6 mm long, glabrous; tepals 2–4, spreading, outer 2 lanceolate to oblanceolate, 3–4 × 0.75–2.5 mm, apex obtuse to rounded, white, glabrous, margin entire, aciliate, inner 1–2 elliptic if present, 3–4 × 0.75–1.25 mm, apex obtuse to rounded, white, glabrous, margin entire, aciliate; stamens 2 or 4, projecting, yellow, filaments 0.25– 0.75 mm long, united on a column, anthers ellipsoid, 0.75–1.5 × 0.25 mm, dehiscing via lateral slits, connectives not extended, symmetrically basifixed. Pistillate flowers: pedicels to 5 mm long; bracteoles absent; tepals 2 or 3, equal, deciduous in fruit, spreading, the narrowly elliptic to oblanceolate, 3–4.5 × 0.75–2.5 mm, apex obtuse to rounded, white, glabrous, margin entire, aciliate; ovary body ovoid, 1.5–2.5 × 1–2.5 mm, pale green, glabrous, sub-equally 2- or 3-winged, wings rounded-oblong, 2–2.5 × 1–1.75 mm; 2- or 3-locular, placentae branches entire, bearing ovules on both surfaces; styles 2 or 3, yellow, free, 2–3 mm long, once-divided, stigmatic papillae in a spiral band. Fruiting pedicel to 5 mm long. Fruit body globose, to 2.5 × 2.5 mm, drying brown, wings same shape and size as in ovary.

Proposed conservation assessment

Assessed by Moonlight et al. (2017a) as Critically Endangered (CR B2ab(iii)) because its single known locality was under threat from a tourist development in Parque Nacional Yanachaga-Chemillén. The proposed development has been cancelled, but the species remains vulnerable because of its extremely limited range and the fact that the locality is frequently visited by tourists. Accordingly, we recommend B. elachista remains categorised as Critically Endangered (CR B2ab(iii)).

Identification notes

Begonia elachista is the smallest Begonia in Peru and possibly the world. It is the only South American Begonia that reaches <5 cm in height and has leaves that only reach 3 × 2.5 cm in size.

Distribution and ecology

Endemic to Peru and known from a single population in Oxapampa Province, Pasco Region ( Fig. 78A ). Found in Amazonian forest at an altitude of ca 430 m a.s.l., where it has been collected on a small, limestone outcrop and the surrounding rocks. Begonia elachista is tuberous and may be dormant during the dry season.

Figures

Fig. 78. Distribution ofBegonia sect.Microtuberosa Moonlight & Tebbitt andB. sect. Pilderia (Klotzsch) A.DC. in Peru and surrounding countries. A. B. elachista Moonlight & Tebbitt (red). B. B. buddleiifolia A.DC. (red). Black lines indicate country borders, grey lines indicate major administrative divisions, blue lines indicate rivers, and shading indicates elevation.

Fig. 79. Begonia elachista Moonlight & Tebbitt. A. Habit. B. Staminate flower, front view. C. Infructescence.D. Pistillate flower, side view. E. Stamens, front view.F. Stamens, side view.G. Pistil, back view. H. Pistil, front view. Illustration by Claire Banks from P.W. Moonlight & A. Daza 318 (E). Reproduced from Moonlight et al. (2017a), with the permission of European Journal of Botany.