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Gardens' Bulletin Singapore 70 (1): 155–161. 2018
doi: 10.26492/gbs70(1).2018-14
Taxonomic status of Begonia promethea (sect. Petermannia,
Begoniaceae) in Borneo
R. Kiew1, S. Julia2, C.Y. Ling2, A. Randi3, D. Girmansyah4 & M. Hughes5
1Forest Research Institute Malaysia,
52109 Kepong, Selangor, Malaysia
2Botanical Research Centre, Sarawak Forestry Corporation,
KM20, Jalan Borneo Heights, Semengoh,
93250, Kuching, Sarawak, Malaysia
juliasang@sarawakforestry.com
3Faculty of Forestry, Bogor Agricultural University,
Kampus IPB Darmaga PO Box 168, 16001 Bogor, Indonesia
4Botany Division, Research Center for Biology,
Indonesian Institute of Sciences, Jl. Raya Jakarta Bogor Km. 46,
Cibinong 16911, Bogor, Indonesia
5Royal Botanic Garden Edinburgh, 20A Inverleith Row,
Edinburgh EH3 5LR, Scotland, U.K.
ABSTRACT. The rediscovery of Begonia promethea Ridl. for the rst time since its description
in 1906 led to the discovery that the later described B. beccarii Warb. is synonymous with it and
that it belongs in Begonia sect. Petermannia. It is a rare, endangered species known only from
three localities, two locations from the Kuching Division, Sarawak, Malaysia and another one
from West Kalimantan, Indonesia. A detailed, illustrated description and a distribution map of
Begonia promethea are provided. We suggest an IUCN conservation category of EN B2ab(iii).
Lectotypes for both names are designated.
Keywords. Begonia beccarii, conservation, Sarawak, taxonomy
Introduction
Begonia promethea Ridl. is an attractive, variegated species described by Ridley
(1906), who suggested that among the species he had described it was a very pretty
begonia ‘perhaps the most worthy of cultivation’ among the Bornean species. More
than a century after its description, Begonia promethea was recently rediscovered in
Sarawak by Michael Lo, a local naturalist, with a further population being found in
West Kalimantan just south of the border with Sarawak by a joint expedition between
Herbarium Bogoriense and the Royal Botanic Garden Edinburgh. These discoveries
enabled us to prepare a complete description and illustration, determine that the later
described Begonia beccarii Warb. is synonymous with B. promethea, and conclude
that it belongs in Begonia sect. Petermannia.
Gard. Bull. Singapore 70 (1) 2018
156
Taxonomy
Begonia promethea Ridl., J. Straits Branch Roy. Asiat. Soc. 46: 259 (1906). – TYPE:
Borneo, Sarawak, Bau District, Buso, Bukit Tundong, September 1903, Ridley 12394
(lectotype K [K000761102], designated here). (Fig. 1 & 2)
Begonia beccarii Warb., syn. nov., Repert. Spec. Nov. Regni Veg. 18: 329 (1922). –
TYPE: Borneo, Sarawak, ‘Pinindgiao’ [Peninjau], November 1865, Beccari PB1013
(lectotype FI [4494], designated here; isolectotypes B [B100238115, B100238116], FI
[4494A], K [K000761103], P [P06844102]).
Low herb with short creeping stem 2–10 cm long, clinging to the rock surface. Stem to
0.5 cm thick, red-brown, unbranched; internodes 0.8–1.8 cm long, slightly thicker at
the nodes. Stem, petiole and lower surface of veins hirsute, hairs whitish or brownish,
2–3 mm long. Stipules broadly lanceolate, 7–12 × 4–8 mm, pale brown or pale brown,
glabrous, keeled, apex setose, seta 3–5 mm long, persistent. Leaves 2–3, rarely 4, the
remains of rotten old leaves sometimes still present, at on the rock surface; petiole
red or reddish brown, hirsute, hairs white, c. 2 mm long, terete, 2–4.3 cm long; lamina
obliquely ovate, sometimes almost orbicular, 8.5–17.5 × 8.5–17 cm, broad side 5.5–11
cm, base cordate, slightly overlapping, basal lobe 1–2.5 cm, apex obtuse, usually dark
green to emerald green above with a broad pale green margin and random spots or
pale green stripes between the veins or rarely plain coloured above, purple to pale
purple below, glabrous above, below hirsute with rows of stiff short reddish hairs on
the veins, margin ciliate, hairs reddish; young leaves red brown; venation palmate, 6–7
veins radiating from the petiole attachment, branching 1–2 times towards the margin,
veins impressed above, raised below. Inorescences 1–3 per plant, protogynous,
racemose-cymose, 14–26 cm long, basal branch with 1–2 female owers, upper
distal branches dichasially cymose with many male owers opening when the female
owers are almost over, peduncle 7–15 cm long, glabrous, reddish, lateral branches
sometimes zig-zag. Bract pale green, keeled, ovate, 12–15 × 3–4 mm, apex setose,
seta to 2 mm long, persistent; lower bracteoles pale green, slightly smaller than bract,
lanceolate, 4–5 × 4 mm, upper bracteoles c. 5 × 2 mm, setose, seta to 2 mm long.
Staminate ower: pedicel pink or white, 2–7 mm long; tepals 2, outer part pinkish,
inner part white tinged pink, heart-shaped, 9–10 × 7–11 mm, stamen cluster rounded,
torus rather thick, stamens 56–67, lemon yellow, laments 0.8–1 mm long, anthers
obovate, 0.6–0.8 × 0.6 mm, apex deeply emarginate. Pistillate ower: pedicel pinkish
or pale green, 12–15 mm long; ovary pale green, 9–11 × 12–15 mm, wings pale green
tinged reddish on the margin; tepals 5, outside pinkish or whitish, inside whitish, 4
outer tepals larger, ovate, c. 9 × 6–7 mm, inner tepal narrower, white, elliptic, c. 8 ×
3–4 mm; styles 3, stigmas 3, rarely 4, anchor-shaped, yellow. Fruits 2–4 per plant,
pedicel pendent, 12–14 mm long; capsules 12–15 × 12–19 mm, wings equal, rounded,
c. 7 mm wide; locules 3, each with 2 placentas.
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Begonia promethea in Borneo
Fig. 1. Begonia promethea Ridl. A. Habit. B. Stipule and stem. C. Upper surface of leaf. D.
Lower surface of leaf. E. Inorescence. F. Male ower. G–H. Female ower. I. Dehisced
fruits. J. Cross-section of female ower. All from SFC 8354. (Photos: C.-Y. Ling)
Distribution. Known from only three sites, two in the Bau District, Sarawak (Bukit
Peninjau, near Mt Serambu, and Buso), and one in the Bengkayang Regency, West
Kalimantan (Berawat’n Waterfall near Gunung Niut) (Fig. 3).
Gard. Bull. Singapore 70 (1) 2018
158
Habitat. Lowland forest at 50–150 m elevation, growing on wet, shaded and almost
vertical sandstone cliffs (Buso) or basalt cliffs with water spray, sometimes in direct
sunlight (Berawat’n Waterfall). Very local but can densely cover the rock face in small
Fig. 2. Habit of Begonia promethea Ridl. in Bengkayang, West Kalimantan (inset: inorescence
showing basal female ower and distal male owers). All from WEKBOE 185. (Photos: A.
Randi)
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Begonia promethea in Borneo
patches. It apparently owers seasonally with peak owering towards the end of the
year in the rainy season. Ridley (1906) had noted that plants he grew in the Botanic
Gardens, Singapore ‘grew very readily and owered in December and January’. Recent
visits to the wild populations in Sarawak showed owering increased from November
to December suggesting that it owers seasonally in the rainy season; owering plants
were seen in West Kalimantan in December.
Etymology. The meaning of the specic epithet is obscure. Prometheus was the Greek
god who fashioned clay to create the rst people, and who was chained to a rock to
have his liver pecked out by an eagle for all eternity as a punishment for stealing re
from the gods and giving it to humanity. Ridley gives no hint as to the connection
between him and this begonia, but we speculate it may be due to the isolated sandstone
rocks on which the species grows, where Ridley noted he ‘could reach but few plants
of it’.
Provisional IUCN conservation assessment. Endangered (EN B2ab(iii)), based on
there being only three known localities with a total area of occupancy <500 km2
and a continued observed decline in the quality of habitat (IUCN, 2012). All known
Fig. 3. Distribution of Begonia promethea Ridl. in Borneo based on conrmed herbarium
specimen records.
Gard. Bull. Singapore 70 (1) 2018
160
localities are located outside of Totally Protected Areas and populations are threatened
by habitat disturbance, although the inaccessible cliff habitat will afford the species
some protection. Only ve mature individuals were noted in West Kalimantan at
Berawat’n Waterfall although much of the cliff was out of reach and it is likely further
individuals exist. Many individuals with all life stages such as seedlings, owering
and fruiting individuals were observed in its habitat in Sarawak.
Additional specimens examined. BORNEO. Sarawak: Bau District, Buso (1.2719 N 110.0947
E), 10 April 2017, Julia et al. SFC 8354 (SAR). West Kalimantan: Bengkayang Regency,
Berawan Waterfall, 10 December 2017, Randi et al. WEKBOE 185 (BO).
Notes. The similarity of Begonia beccarii to B. promethea had already been indicated
because the FI duplicate of the type collection of B. beccarii had been determined
as B. promethea by E. Irmscher (Hughes et al., 2015, continuously updated). The
protologues of the species are similar apart from the length of the inorescence (c. 22
cm in Ridley’s description and 12 cm in Warburg’s) but this is likely due to the state
of development of the inorescence. However, Begonia promethea was problematic
because the type could not be located (Hughes, 2008) and the description of B. beccarii
was incomplete, lacking data for the pistillate ower and fruit. Discovery of wild
populations with individuals in all stages of development has enabled a reassessment
of these two species, with the conclusion that they are the same and that Begonia
promethea takes priority over B. beccarii.
Hughes (2008) stated that the syntypes of Begonia promethea were Haviland
188 and 485 and that they had not been located. However, Ridley (1906) also noted
the plant was found on ‘sandstone rocks at Bukit Tendong near Busau’ (now spelled
Bukit Tundong and Buso), and it is obvious his detailed description was based on
living plants. This indicates that Ridley’s own collection (Ridley 12394) is also a
syntype, which we therefore designate as the lectotype. A further specimen of Begonia
promethea was collected by Beccari from Gunung Skunyet in Sarawak (Beccari
PB1050, FI); the sheet is a mixed collection with B. pendula Ridl. We are not sure
whether this represents a reliable locality record for B. promethea, or whether it was
mounted with the supercially similar B. pendula collections in error.
Begonia promethea and B. beccarii were unplaced to section in Hughes (2008)
while Hughes et al. (2015, continuously updated) noted that B. promethea belonged to
Begonia sect. ?Petermannia. Ridley (1906) included Begonia promethea in Begonia
sect. Bractibegoniae, whilst Warburg (1922) suggested that B. beccarii might belong
to Begonia sect. Reichenheimia based on its habit. Indeed, this species is unusual for
Begonia sect. Petermannia because it grows on vertical cliffs with its leaves at against
the rock surface. However, its protogynous inorescence and ovary with two placentas
per locule show without a doubt that it belongs in Begonia sect. Petermannia.
ACKNOWLEDGEMENTS. We would like to thank Michael Lo for informing us about the
locality of the species in Sarawak. Assistance by Sirukit Dubod during the trip to Buso, and by
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Begonia promethea in Borneo
Hasri Nurfadillah Rahyu Ningsih, Andre Renaldo and Bento during the trip to West Kalimantan
is greatly appreciated, and we are grateful to Mr Tan Jiew Hoe for providing nancial support
for our work on begonia in Sarawak. The Royal Botanic Garden Edinburgh is supported by the
Scottish Government’s Rural and Environment Science and Analytical Services Division. We
also thank RISTEK Indonesia and the Director of the Research Centre for Biology, LIPI, for
their support (permit 391/SIP/FRP/E5/Dit.KI/XI/2017).
References
Hughes, M. (2008). An Annotated Checklist of Southeast Asian Begonia. Edinburgh: Royal
Botanic Garden Edinburgh.
Hughes, M., Moonlight, P., Jara, A., Tebbitt, M., Wilson, H. & Pullan, M. (2015, continuously
updated). Begonia Resource Centre. http://elmer.rbge.org.uk/begonia/. Accessed 9 Jan.
2018.
IUCN (2012). IUCN Red List Categories and Criteria: Version 3.1, 2nd ed. Gland, Switzerland
and Cambridge, UK: IUCN.
Ridley, H.N. (1906). Begonias of Borneo. J. Straits Branch Roy. Asiat. Soc. 46: 247–261.
Warburg, O. (1922). Plantae novae Borneensis. Repert. Spec. Nov. Regni. Veg. 18: 327–330.
