Begonia elachista Moonlight & Tebbitt
Creators: name: Moonlight, Peter. W.
name: Jara-Muñoz, Orlando A.
name: Purvis, David A.
name: Delves, Jay
name: Allen, Josh P.
name: Reynel, Carlos
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Cucurbitales
Begoniaceae
Begonia
Begonia elachista

description: 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.
description: Published as part of Moonlight, Peter. W., Jara-Muñoz, Orlando A., Purvis, David A., Delves, Jay, Allen, Josh P. & Reynel, Carlos, 2023, The genus Begonia (Begoniaceae) in Peru, pp. 1-334 in European Journal of Taxonomy 881 on pages 246-248, DOI: 10.5852/ejt.2023.881.2175, http://zenodo.org/record/8178280