Begonia elachista Moonlight & Tebbitt, 2017

Peter Watson Moonlight, Carlos Reynel & Mark Tebbitt, 2017, Begonia elachista Moonlight & Tebbitt sp. nov., an enigmatic new species and a new section of Begonia (Begoniaceae) from Peru, European Journal of Taxonomy 281, pp. 1-13 : 5-9

Begonia elachista Moonlight & Tebbitt sp. nov. sect. Microtuberosa

http://www.ipni.org/urn:lsid:ipni.org:names:77160201-1

Figs 2 , 3

Diagnosis

Begonia elachista sp. nov. is a highly distinct species with an unusual combination of features that is easily recognized as the only Peruvian species of Begonia that reaches maturity at fewer than 5 cm in height. It is also unique within Peru in having ovate leaves smaller than 3 × 3 cm and a combination of entire placentae and a tuberous habit.

Etymology

The epithet ‘ elachista ’ comes from the Greek for ‘least’ and emphasizes the diminutive size of this species, which is the smallest known species of Begonia .

Type

PERU: Region Pasco, Prov. Oxapampa, Dist. Palcazu, Parque Nacional Yanachaga-Chemillén, sector Paujil, 150 m from entrance to Las Cavernas on trail from Paujil , 10°20ʹ40ʺ S, 75°15ʹ1ʺ W, 432 m, 25 Feb. 2016, Moonlight & Daza 318 (holo-: MOL ; iso-: E , MO , USM ).

Additional material

PERU: Region Pasco, Prov. Oxapampa, Dist. Palcazu, Parque Nacional Yanachaga-Chemillén, sector Paujil, Quebrada Tunel , 10°20ʹ S, 75°15ʹ W, 429 m, 17 Mar. 2008, Vásquez, Monteagudo, Huamantupa & A. Peña 34030 ( E, HOXA, HUT, MO, USM) .

Description

Caulescent, tuberous herb. Tuber subglobose, 1–2 mm in diam. Stems 1–3 per tuber, erect, ca 0.2 mm in diam., 5–30 mm long, unbranched, internodes 1.5–7.5 mm long, glabrous, light green. Stipules persistent, narrowly lanceolate, 0.5–1.5 × 0.2–0.5 mm, apex acuminate, aristate, terminal hair ca 0.4 mm long, margin entire, with 1–2 ciliate hairs to 0.2 mm on each side. Leaves 1–4, alternate, basiFxed; petiole orientated in same direction as the main vein of blade, 8–25 mm long, glabrous, blade symmetrical to subsymmetric, ovate to suborbicular, 8–30 × 7–25 mm, membranous, apex obtuse, base cordate, basal lobes not overlapping, sinus 0.5–2 mm deep, margin irregularly crenate, ciliate, the hairs to 0.3 mm, upper surface glabrous, light grey-green, lower glabrous, light grey-green, veins palmate, 5–7, secondary veins indistinct. InForescences 1–2, axillary, arising from axis of each leaf, erect, an asymmetric dichasial cyme, with 1–2 branches, bearing up to 2 male Fowers and up to 2 female Fowers, usually protandrous but basal-most female Fower often opening concurrently with the apical male Fower; peduncle 5–40 mm long, glabrous; pedicels of male Fowers 2–6 mm long, glabrous; pedicels of female Fowers 1–5 mm long, glabrous; bracts persistent, elliptic, 1.5–2.5 × 0.1–0.3 mm, apex acuminate, margin entire, glabrous or with up to 2 ciliate hairs to 0.2 mm on each side, dark brown. Male Fowers: tepals 2–4, spreading, white, outer two lanceolate to oblanceolate, 3–7.5 × 1–2.5 mm, apex obtuse to rounded, margin entire, glabrous, inner 1–2 elliptic if present, 3–4 × 0.75–1.25 mm, apex obtuse to rounded, margin entire, glabrous; stamens 2 or 4, yellow, Flaments 0.25–0.75 mm long, united on a 0.75–1 mm column, anthers elliptic, 0.75–1.5 mm long, often with long and short thecae on the same anther, dehiscing via lateral slits, connectives not projecting, symmetrically basiFxed. Female Fowers: bracteoles absent; tepals not persisting in fruit, 2 or rarely 3, spreading, white, narrowly elliptic to oblanceolate, equal, 3–4.5 × 0.75–2.5 mm, apex obtuse to rounded, margin entire, glabrous; ovary body ovoid, 1.5–2.5 × 1–2.5 mm, glabrous, white, subequally 2–3-winged, wings rounded-oblong, apical edge of wing truncate to convex, basal edge rounded, apex acute to obtuse, 2–2.5 mm long, 1–1.75 mm wide; 2–3-locular, placentas entire, bearing ovules on both surfaces; styles 2–3, yellow, free to base, 2–3 mm long, biFd from about ⅔ their height, stigmatic papillae in a once spirally twisted band. Fruiting pedicel to 5 mm long. Fruit body globose, to 1.5–2.5 × 2–2.5 mm, glabrous, drying brown, wings same shape and size as in ovary. Seeds not examined.

Distribution and habitat

Begonia elachista sp. nov. is known only from the type locality in the Peruvian region of Pasco (Oxapampa Province) and has been collected on calcareous rocks by the entrance to a cave within primary lowland Amazonian forest, at an altitude of 430 m. It was observed growing on rocks free from other vascular plants in association with various bryophyte species in the almost continual shade of the surrounding forest.

Conservation status

The known range of B. elachista sp. nov. consists of the area immediately around a single cave mouth and nearby limestone outcrops in sector Paujil of Parque Nacional Yanachaga-Chemillén (AOO <1 km 2). There are no other known limestone outcrops in sector Paujil of Parque Nacional Yanachaga-Chemillén or the surrounding areas thus its range is likely limited to this site. Around 5,000 plants are found at this locality and the population appeared stable during Feldwork in February 2016. Although the area is currently protected and tourists are prohibited from visiting the site, the national park authorities are considering building a tourist trail to the cave. The resulting increased footfall would put considerable pressure on the species’ habitat and inevitably decrease the population size. Accordingly, we classify B. elachista sp. nov. as Critically Endangered: CR B2 ab(iii) ( IUCN 2001).

Discussion

The tuberous habit and western South American range of B. elachista sp. nov. suggest a close relationship with other tuberous Andean species of Begonia but this is not supported by our analysis. The majority of tuberous Andean Begonia species are currently classiFed in B. sect. Eupetalum , which is distinguished by its geophytic tubers or Feshy rhizomes and relatively large Fowers ( Doorenbos et al. 1998; Tebbitt 2015). All other tuberous Andean species are classiFed within B. sect. Barya , B. sect. Knesebeckia and B. sect. Quadriperigonia, and all four sections differ from B. elachista sp. nov. in a suite of characters including their biFd placentae (except B. lutea L.B.Sm. & B.G.Schub. ), more numerous stamens and female tepals, and much larger size. We resolve B. sect. Microtuberosa sect. nov. as distantly related to all tuberous species of Andean Begonia and most closely related to rhizomatous and scandent sections from southeast South America. The morphological differences between B. sect. Microtuberosa sect. nov. and these sections are outlined above ( Table 1 ) and, in combination with the placement of B. elachista sp. nov. outside of these sections, strongly support the description of a new section.

The large morphological disparity between B. elachista sp. nov. and its nearest relatives is typical of that found in limestone cave endemics ( Chung et al. 2014). Such species are typically small, often tuberous or rhizomatous, and usually have relatively symmetrical leaves and small, white Fowers. Examples of this syndrome in Begonia are found across sections and continents and include B. antsingyensis Humb. ex Keraudren & Bosser sect. Quadrilobaria A.DC. (Madagascar); B. cavum Ziesenh. sect. Knesebeckia (Klotzsch) A.DC. (Mexico); B. hoehneana Irmsch. sect. Unassigned (Brazil); B. exigua Irmsch. sect. Begonia (Brazil) ; B. minuscula Aver. sect. Reichenheimea (Klotzsch) A.DC. (Vietnam); B. schulziana Urb. & Ekman sect. Begonia (Haiti) ; B. speluncae Ridl. sect. Reichenheimea (Klotzsch) A.DC. (Borneo); and many others. This striking convergence among unrelated Begonia species on similar substrates in Begonia is worthy of further investigation.

That B. sect. Microtuberosa sect. nov. is nested within a group of eastern Brazilian species suggests it represents an independent dispersal across the Amazon basin, in addition to those identiFed in Moonlight et al. (2015). The majority of lowland Amazonia represents unsuitable habitat for most Begonia species but the genus appears to have dispersed across the area multiple times. The discovery of a further dispersal event highlights the abundance of ‘rare’ long-distance dispersal events within Begonia .

Begonia elachista sp. nov. is one of a number of recently described species of Peruvian Begonia . The number of species known from this country has risen from the 34 covered in the Flora of Peru ( Smith & Schubert 1941) to more than 75 today ( Hughes et al. 2015). This continued rapid rate of species discovery suggests many more species may remain undiscovered within the country, particularly in limestone areas.

A number of species are contenders for the world’s smallest Begonia , and many have been designated epithets emphasising their diminutive statures. The Frst of these was B. minor Jacq. in 1787, although in this case the name only implied it was slightly smaller than the 20 or so species previously described, and it still grows to more than 1 m. Perhaps the most delicate known Begonia species is the Malaysian B. sibthorpioides Ridl. , whose leaves and Fowers are both smaller than those of B. elachista sp. nov.; however, the stem of B. sibthorpioides trails to 10 cm. Malagasy Begonia also include a number of tiny species, including B. leandrii Humb. , B. nana L’Hér. and B. perpusilla A.DC., while the smallest mainland African species is B. wilksii Sosef , but all exceed the 3 cm total height of B. elachista sp. nov. in either their inForescence height or petiole length. The recently described Vietnamese B. minuscula Aver. and Sumatran B. lilliputana M.Hughes are both small, but the rhizomes of the former reach 6 cm while the leaf length of the latter equals the entire height of B. elachista sp. nov. Begonia sleumeri L.B.Sm. & B.G.Schub. is particularly notable in being a small tuberous species from Andean South America. This Argentinian species has smaller leaf blades of a similar size (1–3.1 × 1.4–4.6 cm) to B. elachista sp. nov. but has larger tubers (0.5–2 cm in diam.), sometimes has taller stems (up to 4.5 cm tall), often has longer petioles (1.2–5.3 cm long), and almost always has larger Fowers. We believe B. elachista sp. nov. is the smallest known Begonia species in the world.

Figures

Fig 2. Begonia elachista Moonlight & Tebbitt sp. nov. A. Habit. B. Male Fower, front view. C. Branch of infructescence. D. Female Fower, side view. E. Stamens, front and side view. F. Style, front and back view. Scale bars: A – D = 1 cm; E – F = 1 mm. Drawn by Claire Banks. From P. Moonlight & A. Daza 318 (E).

Fig 3. Begonia elachista Moonlight & Tebbitt sp. nov. A. Whole plant. B. Male and female Fower, front view. C. Female Fower, side view. D. Habit and associated vegetation. E – F. Habitat and wild population. Scale bars: A = 1 cm; B = 5 mm; C = 2 mm; D = 2 cm; E – F = 10 cm. Photographed by Peter Moonlight. All from P. Moonlight & A. Daza 318 (E).