Begonia bukitrayaensis Randi & Mustaqim, 2025

Randi, Agusti, Mustaqim, Wendy A., Kadhafi, Andi M., Nursub’I, Firasadi & Ardi, Wisnu H., 2025, Two new species of Begonia (Begoniaceae) from Bukit Baka Bukit Raya National Park, Kalimantan, Indonesia, Phytotaxa 704 (2), pp. 99-105 : 100-102

Begonia bukitrayaensis Randi & Mustaqim , sp. nov. §. Petermannia ( Fig. 1 )

Type: — INDONESIA. West Kalimantan: Sintang Regency, Serawai District, Rantau Malam Village , Soa Tohotung camp area of Bukit Baka Bukit Raya National Park , 0°39’33.3”S, 112°39’44.7”E, 1500 m elev., 2 Jul 2024, Mustaqim & Yudistira 3364 (holotype WAN!; isotypes BO!, FIPIA!) .

Diagnosis: — Begonia bukitrayaensis is similar to Begonia chakensis S.Julia & C.Y.Ling (2015: 108) in its creeping habit and ovate, asymmetric leaves, but differs in having glabrous vegetative parts except for stiff red bristle-like trichomes between the veins on the adaxial leaf surface (vs. densely pilose stems, petioles, and abaxial veins in B. chakensis ). The leaves of B. bukitrayaensis have red-dentate margins and a rounded to slightly cordate base (vs. minutely serrate margins and an acute or slightly cordate base). The stipules are falcate with recurved margins and a cuspidate apex (vs. broadly ovate, serrate, and acute). Male flowers bear fewer stamens (25–28 vs. 39–40).

A terrestrial creeping herb up to 70 cm long, often branched; whole plant glabrous except the adaxial side of the leaf lamina. Stem succulent, 3–7 mm in diameter, plain green, sometimes reddish to light brown in old stem, rooting on each node when in contact with the substrate; nodes slightly swollen, internodes 1–5 cm apart. Stipules persistent, asymmetric, lanceolate to elliptic or falcate, 14–25 × 7–11 mm, glabrous and light green on both sides, midrib sunken on adaxial surface, strongly prominent abaxially, margin entire and becoming recurved with ageing, apex cuspidate with hardened and pointed ends. Leaves alternate, glossy and glabrous entirely; petiole 2–6 cm long, 2–4 mm diameter, channeled adaxially and rounded abaxially, light green or sometimes reddish at the ends; lamina strongly asymmetric, ovate to kidney-shaped, 7–14 × 5–9 cm, base rounded to slightly cordate, generally yellowish to reddish, margins broadly dentate with thin red along its edge, apex acuminate to caudate; adaxial surface light to emerald green, hairs are modified into red thick spine-like bristles resembling cat’s claw, up to 2 mm long, sparsely distributed between the venations, bright red to crimson; abaxial surface pale green; venation palmate-pinnate, actinodromous, midrib distinguishable with 2–3 lateral veins each side, other primary veins branching dichotomously. Inflorescence protogynous, raised terminally, erect, up to 28 cm long, 1.6–3.5 mm diameter at base, light green; peduncles, pedicels, flower tepals, and ovary milky white when fresh; pistillate flowers in pairs on each node, up to 3 pairs along 2/3 of inflorescence length, each pair resting on a stalk 2–5 cm long; upper inflorescence up to 9 cm long with cymose branching to 2 orders containing up to 15 staminate flowers; bracts similar as stipules but often with symmetric base; bracteoles broadly ovate to suborbicular, 7–12 × 8–14 mm, margin entire, apex vary from acute, acuminate, rounded to shallowly emarginate. Staminate flower with 4 tepals, 2 outer and 2 inners, all with entire margins; pedicel slender, 9–14 mm long, 0.7–1.2 mm diameter; outer tepals broadly ovate to suborbicular, 9–14 × 8–14 mm, apex obtuse to rounded; inner tepals much narrower than outer ones, narrowly elliptic to linear, 5–8 × 1–2 mm, apex acute to rounded; androecium symmetric, 3–4 mm high, with 25–28 yellow stamens; filament slender, 0.6–1.4 mm long, anthers obovate, 0.8–1.5 × 0.5–1 mm, with divided apex, opened by slit. Pistillate flower 20–29 mm across at anthesis; pedicel 8–12 mm long, 0.8–1.1 mm diameter; ovary 3-locular, asymmetric, 12–15 × 13–17 mm (wings included), placentae bifid; tepals 5, 2 outer and 3 inners, all with entire margins; outer tepals ovate, 12–16 × 9.5–11 mm, apex obtuse to rounded; inner tepals with 2 broader and 1 smaller, broader ones asymmetric, broadly elliptic, 12–18 × 6–7.5 mm, apex rounded, smaller one distinctively smaller, narrowly elliptic, 10–14 × 2.5–3.5 mm, apex acute or sometimes obtuse; styles 3, 3–4 mm long, bifid, golden yellow; stigmas anchor-shaped, forming a short papillose spiral band. Fruit peduncle 14–36 mm long, light green; pedicel 12–23 mm long; capsules reflexed, 12–17 × 12–18 mm (wings included); milky white to light green, glabrous; wings 3, subequal, 3–5 mm wide at the widest point, apex rounded.

Distribution: —Endemic to Kalimantan, Borneo: found in Mount Bukit Raya in the Bukit Baka Bukit Raya National Park located on the border of West and Central Kalimantan Province ( Fig. 3 ).

Ecology and Habitat: —Terrestrial, creeping on mossy granite rocks in the banks of small rocky rivers and on the clay soils among granite-derived rocks on humid areas from the lowland mixed dipterocarp forest at 700 m elev. to the montane forest at 1650 m elev.

Etymology: —The epithet refers to the name of the location where this species was found, Mount Bukit Raya.

Provisional Conservation Status: —Least Concern (LC) ( IUCN, 2024). Begonia bukitrayaensis is found in the lowland to montane forest of Mount Bukit Raya. The location is open to tourists who climb to the top of the mountain, which is one of the seven summits in Indonesia, but the localities of the populations of this new species are not easy to find and are relatively hidden. Although based on EOO = 0.735 km ², and AOO = 12 km ² this species potentially qualifies for the critically endangered category, but we have observed that this species is growing commonly in undisturbed forests and in fully protected forest areas of the national park.

Additional specimen examined: — INDONESIA. West Kalimantan: Sintang Regency, Serawai District, Rantau Malam Village , Soa Tohotung camp area on the hiking trail to the Bukit Raya’s summit, 0°39’34.5”S, 112°40’14.3”E, 1640 m elev., 3 July 2024, Mustaqim & Yudistira 3373 ( BO!, FIPIA!, WAN!) ; Bukit Raya summit trail, 1650 m elev., 6 June 2015, A. Randi AR-406 ( BO!) .

Notes: —Imbricate bract and bracteoles are a rare character in the section Petermannia , and primarily found in the Bornean species such as B. chakensis , B. imbricata Sands (1990: 68) , B. dolichobracteata Girmansyah (2015: 19) , B. bosuangiana S.Julia ( Repin et al. 2015a: 6), and B. kumangiana S.Julia & C.Y.Ling ( Julia & Ling 2022: 18). Among of these species, B. chakensis bears the most resemblance to B. bukitrayaensis , and the differences between these two species are discussed in the diagnosis. The new species also superficially resembles B. bosuangiana and B. kumangiana in having a creeping habit, but these two species can easily be distinguished from their stems and petioles that are consistently hirsute (vs. glabrous in B. bukitrayaensis ). Meanwhile, B. imbricata and B. dolichobracteata are clearly different from B. bukitrayaensis from their erect habit (vs. creeping).

Figures

FIGURE 1. Begonia bukitrayaensis Randi & Mustaqim. A. Plant habit; B. Stipule and petiole; C. Leaves on abaxial surface; D. Hairs that harden like thorns on adaxial surface of leaves; E. Inflorescence; F. Cross section of fruit; G–H. Staminate flower (side and top view); I–J. Pistillate flower (side and top view). Photographs: A–D by A. Randi (from AR-406), E–J by Wendy A. Mustaqim (from Mustaqim et al. 3364).

FIGURE 3. Distribution map of Begonia bukitrayaensis (blue circle), and B. kalimantana (red circles).