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Begonia kabaenensis, Edinburgh Journal of Botany 80: article 1980, 8. 2023
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Diagnosis
- Similar to the sympatric species Begonia batusangiensis in having succulent, ovateto elliptic leaves, but B. kabaenensis can be distinguished by its paniculate-cymosemale inflorescences (vs a simple monochasium or dichasium with few flowers), ashorter female flower pedicel (4–6 mm vs 7–9 mm long), female flowers with 5 tepals(vs 2-tepaled female flowers), well developed ovary wings with a rounded base and subtruncate apex and a subapical widest point up to 6 mm (vs narrow ovary wings with rounded to cuneate base and cuneate apex, widest point in the middle part up to 2 mm); and slightly recurved and shorter fruit pedicels up to 7 mm long (vs strongly recurved, 15–20 mm long). The broadly dentate-denticulate leaf lamina margin and the paniculate-cymose male inflorescence of Begonia kabaenensis are similar to those of B. imperfecta Irmsch.; however, the new species can be differentiated by being monoecious (vs dioecious) and having female flowers with 3 narrow equal wings (vs wingless) and dry, dehiscent capsules (vs fleshy and indehiscent fruit). (Ardi, W.H. & Thomas, D.C. 2023: Three new species of Begonia from the outer islands of Southeast Sulawesi. – Edinburgh J. Bot. 80(article 1980): 4. http://doi.org/10.24823/EJB.2023.1980)
Description
- Perennial, monoecious herb with erect stems, many-branched. Stem erect, soft-wooded at the base, up to 1 cm in diameter, brownish-reddish, glabrous except for microscopic glandular hairs, internodes 2–8 cm long. Leaves alternate; stipules caducous, 16–20 × 8–10 mm, oblong, with an abaxially slightly prominent midrib, apex apiculate, apicule up to 1.5 mm long, margin entire and revolute in mature stipules, brownish, glabrous; petioles 2–14 cm long, terrete, reddish-brownish, glabrous; lamina 7.5–14 × 5–9 cm, asymmetrical, ovate, base cordate and lobes often overlapping, apex acuminate, margin broadly dentate and denticulate in between the larger teeth, adaxial surface green, glabrous, abaxial surface reddish, with sparse hairs on the veins; primary veins 6–8, actinodromous, secondary veins craspedodromous. Inflorescences: protogynous; female inflorescences 1- or 2-flowered, basal to male inflorescences, peduncles (3–)6–12 mm long, pale green, glabrous, bracts semi-persistent, 7 × 4–5 mm, ovate, pale green, translucent; male inflorescences paniculate-cymose (a compound thyrse), with up to 4 or 5 partial inflorescences, cymes monochasially branching with up to 7 flowers, peduncles of partial inflorescences up to 16 mm long, reddish green, glabrous; bracts caducous. Male flowers: pedicels 1–2.2 cm long, whitish, glabrous; tepals 2, white, 11–15 × 13–14 mm, suborbicular to broadly ovate, margin entire, apex rounded; androecium of c.45 stamens, yellow, filaments up to c.1.5 mm long, anthers c.1.2 mm long, obovate, dehiscing through unilaterally positioned slits that are c.1/2 as long as the anthers. Female flowers: pedicels 4–6 mm long, slightly recurved in flower stage, green, glabrous; tepals 5, white, subequal, 15–17 × 7–14 mm, elliptic to slightly obovate, margin entire, apex rounded; ovary (without wings) c.15 × 4 mm, narrowly obovoid to ellipsoid, pale green, wings 3, narrow, convex at base, apex subtruncate, up to 6 mm at the widest point (subapical), style up to 5 mm long, basally fused, 3-branched, each stylodium bifurcate in the stigmatic region, stigmatic surface a spirally twisted papillose band, orange. Fruit: peduncle up to 16 mm long; pedicels up to 7 mm long, greenish-reddish, glabrous, slightly recurved; seed-bearing part c.20 × 6 mm (excluding the wings), ellipsoid, dehiscent, splitting along the wing attachment, wing shape as for ovary, widest point subapically, up to 6 mm wide. Seeds unknown. (Ardi, W.H. & Thomas, D.C. 2023: Three new species of Begonia from the outer islands of Southeast Sulawesi. – Edinburgh J. Bot. 80(article 1980): 4. http://doi.org/10.24823/EJB.2023.1980)
Habitat
- Base of limestone cliffs, in full shade, at 1000–1250 m elevation. (Ardi, W.H. & Thomas, D.C. 2023: Three new species of Begonia from the outer islands of Southeast Sulawesi. – Edinburgh J. Bot. 80(article 1980): 4. http://doi.org/10.24823/EJB.2023.1980)
Conservation
- Proposed IUCN conservation category. CR B1ab(i,ii,iii)+2ab(i,ii,iii). Begonia kabaenensis is known from only two collections from the type location on Gunung Batusangia, Kabaena Island, which has no legal protection status. The species is restricted to the base of vertical walls at caves or shaded cliffs in the upper part of the mountain. It grows in rather inaccessible areas that are difficult to reach for humans, but there is substantial anthropogenic disturbance nearby negatively impacting the margins of the species’ habitat. Most of the lower parts of the mountain have been converted into clove plantations, and the surrounding areas include nickel-mining sites. Because of its very restricted distribution and associated small EOO and AOO, in combination with observed anthropogenic disturbances and likely future habitat loss, we asses this species as Critically Endangered (IUCN Standards and Petitions Subcommittee, 2022). (Ardi, W.H. & Thomas, D.C. 2023: Three new species of Begonia from the outer islands of Southeast Sulawesi. – Edinburgh J. Bot. 80(article 1980): 4. http://doi.org/10.24823/EJB.2023.1980)
Distribution (General)
- Indonesia, endemic to Sulawesi, southeastern Sulawesi, Kabaena Island, Gunung Batusangia.
Etymology
- The species epithet refers to the island of Kabaena, southeastern Sulawesi, where the type material was collected. (Ardi, W.H. & Thomas, D.C. 2023: Three new species of Begonia from the outer islands of Southeast Sulawesi. – Edinburgh J. Bot. 80(article 1980): 4. http://doi.org/10.24823/EJB.2023.1980)A
Notes
- Limestone karst areas in Malesia harbour numerous species of Begonia, many of which are narrow endemics, and its microhabitats generally support a high floristic diversity (Clements et al., 2006). Kiew (1998) observed that calciphile begonias in Sabah showed strong niche partitioning in the limestone habitats of Bukit Dulong (Gomatong Cave). At the shaded base of the cliff, two understorey Begonia species were found (B. gomatongensis Kiew and B. postari Kiew). At slightly higher elevations where the canopy provides less shade and lower humidity, more drought-tolerant species that are adapted to direct sunlight and heat, such as Begonia malachosticta Sands, were found growing in rock crevices in the cliffs of jagged outcrops. Similar conditions were also observed in the limestone karst of Gunung Batusangia, where Begonia kabaenensis and B. batusangiensis occur sympatrically: B. kabaenensis is found growing in humid and shaded habitats at the base of the hill, whereas B. batusangiensis is growing in rock crevice habitats in the vertical limestone cliffs that are exposed to direct sunlight. (Ardi, W.H. & Thomas, D.C. 2023: Three new species of Begonia from the outer islands of Southeast Sulawesi. – Edinburgh J. Bot. 80(article 1980): 4. http://doi.org/10.24823/EJB.2023.1980)