Begonia kalimantana Randi & Ardi, 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 : 102-104

Begonia kalimantana Randi & Ardi , sp. nov. §. Petermannia ( Fig. 2 )

Type: — INDONESIA. West Kalimantan: Sintang Regency, Serawai District, Rantau Malam Village , near Sungai Mangan base camp on the hiking trail to the Bukit Raya’s summit, 0°37’49.19”S, 112°37’27.01”E, 620 m elev., 3 July 2024, A. Randi AR-1366 (holotype WAN!; isotypes BO!, FIPIA!) .

Diagnosis: — Begonia kalimantana resembles Begonia eutricha Sands (1997: 434) in erect habit with distichous and falcate leaves, however it can be easily distinguished by striking consistent color pattern, dark olive green with shiny silvery white stripe along the midrib (vs. plain green), lamina surface hirtellous (vs. densely hispid); shorter male flower pedicels 8–12 mm long (vs. 22–24 mm long); ovary reddish and glabrous (vs. ovary white tinged with pink, and covered with soft white erect hairs), wings margin glabrous (vs. ciliate), and longer ovary beaked 3–5 mm long (vs. 1 mm long).

An erect terrestrial herb up to 30 cm tall, generally unbranched. Stem ascending and curving, 5–12 mm diameter, light green to reddish or brownish green, covered by densely pale yellowish green hispid hairs, internodes 6–22 mm apart. Stipules persistent, flat, covering the stem, petioles and bracts, sometimes also pedicels and ovaries; asymmetric, broadly ovate, 14–18 × 11–15 mm, light green to crimson, glabrous on both sides or with sparse strigose on outer side midrib, margin entire to minutely undulated, translucent, apex acute to retuse, with a long bristle point. Leaves distichous, arranged alternately; petiole short, 3–8 mm long, 2–4 mm diameter, yellowish green to reddish, covered by dense hispid hairs; lamina slightly falcate, elliptic to lanceolate, 11–22 × 3–7 cm, hirtellous on both sides; base cordate, subequal, overlapping, with an auriculate lobe on one side only, margin dentate, or sometimes crenate, ciliate, apex attenuate; adaxial surface has a striking color pattern, dark olive green with shiny silvery white stripe along the midrib and about half the length of lateral veins, minutely bullate; abaxial surface pink with ivory white to cream stripe along its main veins; venation pinnate, midrib conspicuous, slightly raised above, strongly prominent below, lateral veins 6–15 on each side, sunken above, prominent below. Inflorescences protogynous, appear in the leaf axils spread along the stem; male inflorescence a simple cyme, bracts small, triangular with long pointed apex, 3–5 × 1–2 mm, arranged tightly on a short peduncle, 4–6 mm long. Staminate flower: pedicel white, 8–12 mm long; tepals 2, ovate to suborbicular, 6.1–8.0 × 6.4–8.0 mm, white tinged with pink at the margin, glabrous, margin entire, apex rounded or obtuse; stamens yellow, in a loose conical cluster, 20–24, stalk ca. 1 mm long; filaments white tinged with yellow, 1.0– 1.9 mm long; anthers yellow, ca. 1.0 × 0.6 mm, obovate, apex emarginate. Pistillate flower solitary on leaf axils, or sometimes on leafless older stem; with very short pedicel, ca. 1.3 mm long, pink; ovary generally hidden by two stipules, reddish, glabrous, 4–6 × 8–11 mm (wings included), with conspicuous beak, 3–5 mm long; wings falcate, curving upward toward the apex, apex obtuse; locules 3, placentas 2 per locule with many ovules on both surfaces; tepals 5, all glabrous, white or white tinged with pink at apex and margin, margins entire, apex acute to rounded; outermost tepals 2, oblanceolate, 7–8 × 3–4 mm; innermost 3 tepals, oblanceolate to spatulate, white, 8–11 × 3–6 mm; styles 3, persistent, pale yellow, 2–3 mm long, divided near the base, Y-shaped with twisted tips; stigma pale yellow, papillose forming a continuous twisted band. Fruit erect, single in leaf axil, 5–6 × 6–8 mm (wings included), pinkish green when fresh, glabrous, beak persistent, 5–7 mm long; wings 3, subequal, apex rounded, 2–3 mm long; pedicel 1–2 mm long, glabrous.

Distribution: —Endemic to Kalimantan, Borneo. So far only known from Schwaner Mountains of West and Central Kalimantan Province. Two locations are recorded, namely on the Bukit Raya hiking trail near Sungai Mangan base camp in Bukit Baka Bukit Raya National Park in West Kalimantan, and in the Forest Village Tumbang Habangoi in Central Kalimantan ( Fig. 3 ).

Ecology and habitat: —Lowland mixed dipterocarp forest at 200– 700 m.elev. in valleys with dense forest canopy cover, often found growing on slopes near small rivers.

Etymology: —From Kalimantan, Indonesian Borneo.

Provisional Conservation Status: —Least Concern (LC) ( IUCN, 2024). Begonia kalimantana grows in relatively undisturbed primary forests and is located in fully protected forest areas, namely in the national park and the village forest.

Additional examined specimens: — INDONESIA. Central Kalimantan: Katingan Regency, Tumbang Habangoi Forest Village, 0°47’28.23”S, 112°57’13.19”E, 270 m. elev., 26 November 2022, A. Randi AR-882 ( WAN!, BO!).

Notes: — Begonia kalimantana belongs to an informal ‘bruneiana’ group which has reclinate, short, unbranched, stout stems that arch, axillary and sessile inflorescences, and beaked ovary or capsule. Among the species in this group, B. kalimantana is most similar to B. eutricha as discussed in the diagnosis above. Regarding the beaked ovary or capsule B. kalimantana is also similar to B. gusilii Rimi ( Repin et al. 2015b: 175), and B. rambutan Rimi ( Repin et al. 2015a: 16), but it can be easily differentiated by glabrous (vs. hairy) and distinctly winged (vs. wingless) ovary.

Figures

FIGURE 2. Begonia kalimantana Randi & Ardi. A. Plant habit in the wild; B–C. Adaxial and abaxial surface of leaves; D. Stipule; E. Stem and inflorescences; F. Staminate flower (top view); G–H. Pistillate flower (top and side view). Photographs: A. Randi (all from Randi AR-1366).

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