Begonia sojolensis D.C.Thomas & Ardi, 2022

Ardi, W. H. & Thomas, D. C., 2022, SYNOPSIS OF BEGONIA (BEGONIACEAE) FROM THE NORTHERN ARM OF SULAWESI AND SANGIHE ISLAND, INDONESIA, INCLUDING THREE NEW SPECIES, Edinburgh Journal of Botany 79 (405), pp. 1-50 : 41-44

18. Begonia sojolensis D.C.Thomas & Ardi , sp. nov. § Petermannia

Differs from all other Sulawesi species in Begonia sect. Petermannia by its inflorescence morphology. The female flowers are solitary, borne one node below the male inflorescence on a very short side branch (equivalent to the peduncle in species with 2-flowered inflorescences), and the male inflorescence is a compound thyrse with lateral branches bearing 1–3 monochasia, each with short but clearly developed internodes (not strongly compressed like in many other Sulawesi species). This inflorescence morphology, in combination with other distinctive characters such as small male flower tepals (4–5 × 4–5 mm) and the recurved fruit pedicel, differentiate this species from other species in the section.

– Type: Indonesia, Sulawesi, Central Sulawesi, Donggala Regency , Gunung Sojol , 8 viii 2018, W.H. Ardi WI311 (holotype BO; isotypes FIPIA, SING). Figure 13 .

Perennial, monoecious herb, erect, up to c. 40 cm tall. Stem branched, sparsely hairy with bristly hairs and microscopic glandular hairs; internodes 5–8.5 cm long, brownish. Leaves basifixed, alternate; stipules caducous, 6–8 × 2.5–4 mm, elliptic, with an abaxially slightly prominent midrib, apex narrowed into a bristle projecting up to 1 mm, brownish-reddish, abaxially sparsely pubescent; petioles 3–8 cm long, glabrescent, concolorous with the stem; lamina 12.5–19 × 6.5–8.5 cm, asymmetrical, elliptic to obovate, base cordate and lobes not overlapping, apex acuminate, margin subentire, adaxial surface green with very sparse indumentum of bristly hairs between the veins, abaxial surface pale green, hairy with bristle hairs on the veins; venation palmate-pinnate, primary veins (5–)6–7, actinodromous, secondary veins craspedodromous. Inflorescences protogynous; female flowers solitary, borne on short side branches 1–1.5 mm long (equivalent to the peduncle in species with 2-flowered female inflorescences); male inflorescence a compound thyrse with multiple lateral branches, each carrying 1–4 monochasial partial inflorescences, each with 2–10 flowers, peduncle of partial inflorescences up to 1.5 mm long, bracts caducous. Male flowers: pedicels 3–4.5 mm long, white, puberulent; tepals 2, white or white with greenish margin, 4–5 × 4–5 mm, broadly ovate to suborbicular, base slightly cordate, apex rounded, outer surface puberulent; androecium of 23–35 stamens, yellow, filaments 0.5–1 mm long, slightly fused at the very base, anthers 0.5–1 mm long, oblong to obovate, dehiscing through unilaterally positioned slits that are c.1/2 as long as the anthers. Female flowers: pedicels c. 5 mm long, reddish, scabrous; tepals 5, white or white tinged with green, unequal, one smaller, 5 × 2.5 mm, elliptic, four larger tepals 5–9 × 5–7 mm, ovate, outer surface hairy with microscopic, glandular hairs; ovary (excluding wings) 11.5 × 2.5 mm, cylindrical, white-cream, sparsely hairy with short bristly hairs and microscopic glandular hairs, locules 3, placentation axile, placentae bilamellate, wings 3, equal, green, base rounded to cuneate, margin entire, apex truncate, up to 3.5 mm at the widest point (apically or subapically); style c. 3.5 mm long, basally fused, 3-branched, each stylodium bifurcate in the stigmatic region, stigmatic surface a spirally twisted papillose band, orange. Fruits: peduncles 1–2 mm long; pedicels 6.5–10 mm long; seed-bearing part cylindrical, 12–16 × 4–6 mm (excluding the wings), glabrous, dehiscent, splitting along the wing attachment, wing shape as for ovary, up to 6 mm at the widest point (apically or subapically). Seeds barrel-shaped, c. 0.15 mm long.

Distribution. Indonesia: endemic to Sulawesi, Central Sulawesi Province (western North biogeographical region), Gunung Sojol, Toli-toli (see Figure 2 ).

Habitat. Begonia sojolensis grows in lowland forest, in disturbed habitats, on stream embankments and rocky slopes, in full shade, at c. 200 m elevation.

Etymology. The specific epithet refers to the type locality, Mount Sojol, where the type specimen was collected.

Proposed IUCN conservation category. Data Deficient (DD). This species is known from only two localities (the Mount Sojol Forest Reserve and Toli-toli). The forests of Mount Sojol and the wider area are very poorly collected and explored. Consequently, we assess this species as Data Deficient ( IUCN Standards and Petitions Subcommittee, 2019).

Additional specimens examined. INDONESIA. Sulawesi. Northern arm of Sulawesi. Western North Sulawesi: Mt Sojol , 25 ii 2000, Argent et al. 00152 ( E, L) ; Toli-toli , 18 i 2019, Zulfadly ZF 44 ( BO, FIPIA) .

The complex inflorescence architecture (a compound thyrse) with lateral branches bearing multiple monochasia with short but clearly developed internodes (not compressedsubumbellate) immediately differentiate Begonia sojolensis from other Sulawesi Begonia species. This inflorescence morphology, in combination with the relatively small-tepalled male flowers, seems more similar to that of several species of Begonia sect. Petermannia from Borneo, such as B. stenogyna Sands. However , the new species is otherwise morphologically very different: it can be easily differentiated by its smaller habit (up to

40 cm tall) and smaller elliptic stipules (6–8 × 2.5–4 mm), in contrast to B. stenogyna , which is much more robust (up to 2.5 m tall) and has much larger, lanceolate stipules (18–25 × 6–9 mm). The leaf lamina of Begonia sojolensis is elliptic to slightly obovate, as well as smaller (12.5–19 × 6.5–8.5 cm), and the adaxial surface is sparsely hairy with bristly hairs between the veins (vs leaf lamina broadly lanceolate, 15.5–22.5 × 6.2–12.5 cm, and adaxially glabrous). Moreover, the fruit morphology is different and the seed-bearing part of the fruit of Begonia sojolensis is much smaller (1.2–1.6 × 0.4–0.6 cm vs 3.5–4.3 × 0.4–0.7 cm; measurements excluding the wings).

Figures

Figure 2. Distribution maps of Begonia species occurring on the northern arm of Sulawesi. Distribution points are from georeferenced collections from major herbarium collections (B, BO, E, K, KRB, L, SING), the Begonia Resource Centre (Hughes et al., 2015–) and the Sulawesi Begonia Data Portal (Thomas et al., 2013, continuously updated).

Figure 13. Begonia sojolensis D.C.Thomas & Ardi, sp. nov. A, Habit; B, stipule; C, male inflorescence; D, female flower (side view); E, male flower (front view); F, female flower (front view); G, male inflorescence and fruit; H, ovary (cross-section of middle part). A–E, G and H from W.H. Ardi WI311; F from Zulfadly ZF44. Photographs: A–E, G and H, W. H. Ardi; F, Zulfadly.