Begonia matarombeoensis D.C.Thomas & Ardi in Gard. Bull. Singapore 70(1): 168. 2018

Primary tabs

https://drive.google.com/uc?id=1IZr3WsWPu7tw078FCXAh-7NOhrukhU1V

Begonia Section

  • Petermannia

Diagnosis

Description

  • Perennial, monoecious herb, up to c. 30 cm tall; basal stems loosely appressed to the substrate, and rooting at the nodes, distally often ascending to erect; with microscopic glandular hairs and a sparse indumentum of whitish to reddish trichomes, c. 0.5–0.75 mm long, on above-ground vegetative parts. Stem branched, internodes (1.3–)2–6.5 cm long, terete, green or red. Leaves alternate; stipules persistent, 8–15 × 6–12 mm, ovate to broadly ovate, acuminate, setose, seta to 6 mm long, margin entire, pale green, translucent; petioles (1.5–)6.5–21 cm long, terete, reddish; lamina basifixed, 7–19 × 4.5–12.5 cm, asymmetric, elliptic, ovate, broadly elliptic or broadly obovate, basecordate and lobes not or sometimes slightly overlapping, apex shortly acuminate, margin subentire to distantly dentate or serrate, and denticulate between the larger teeth, the teeth bristle-pointed, adaxial surface dark green or green-maroonish, sometimes with small white dots, abaxial surface pale green or maroon, very sparsely hairy on the veins to glabrescent, primary veins 5–7, actinodromus, secondary veins craspedodromus. Inflorescences protogynous; female partial inflorescences 1–2-flowered, usually one node basal to male inflorescences, peduncles up to 4.2 cm long, bracts 4–5 × 2 mm, elliptic. Male inflorescences paniculate-cymose, composed of several monochasial partial inflorescences, monochasia on up to 6 cm long peduncles in the basal part of inflorescence, but subsessile in the most distal part, each monochasium with 3–9 flowers, subumbellate or internodes distinct, bracts elliptic, 4–7 × 2.5–4.5 mm, pale green, translucent. Male flowers: pedicels 11–20 mm long, whitish-greenish, glabrous; tepals 2, broadly ovate to suborbiculate, 8–13 × 9–12 mm, base slightly cordate, margin entire, apex rounded, white or white tinged with pink, glabrous; androecium of (13–)25–39 stamens, yellow, filaments c. 1–1.5 mm long, slightly fused at the very base, anthers c. 0.5–1.5 mm long, obovate, dehiscing through unilaterally positioned slits c. 1/2 as long as the anthers. Female flowers: pedicels 9–11 mm long, glabrous, greenish or green–reddish; tepals (4–)5, white tinged with pink, subequal to unequal and the four outer larger, 11–15 × 5.5–8 mm, elliptic, the inner smaller, 9.5–11 × 4–5 mm, elliptic, glabrous; ovary ellipsoid, 9–15 × 4–10 mm (excluding the wings), pale green, glabrous, locules 3, placentation axile, placentae bilamellate, wings 3, base rounded or cuneate, apex cuneate to subtruncate, style basally fused, 3-branched, each stylodium bifurcate in the stigmatic region, yellow to orange and tinged with pink, stigmatic surface a spirally twisted papillose band, yellow to orange. Fruits: pedicels up to 1.5 cm long, curved downwards at apex, seed bearing part ellipsoid to obovoid, 8–16 × 7–11 mm (excluding the wings), glabrous, dehiscent, splitting along the wing attachment, wing shape as for ovary, up to 5 mm at the widest point (middle part to subapically). Seeds barrel-shaped, c. 0.2–0.3 mm long. (Thomas, D.C., Bour, A. & Ardi, W.H., Begonia of the Matarombeo karst, Southeast Sulawesi, Indonesia, including two new species in Gardens' Bulletin Singapore 70(1): 163-176. 2018)

Habitat & Ecology

Conservation

  • Provisional IUCN conservation assessment. Endangered EN B1ab(iii),B2ab(iii). Begonia matarombeoensis is known from only four collections and several observations from the SE and N of the Matarombeo mountain range, where this species is locally common. Matarombeo is not legally protected, and the species’ currently known EOO and AOO coupled with the detrimental impact of land use (particularly oil palm plantations, but also other threats such as nickel mining) on the habitats at the periphery of the limestone karst, warrants an Endangered (EN) status. As Matarombeo is very poorly explored, this species is likely more widespread within the mountain range than currently known and may also occur in suitable karst habitats in Morowali Regency in Central Sulawesi north of Matarombeo. However, even if this is the case, the extent of suitable karst habitats is still limited, and its EOO and AOO would still fall well in the range for an Endangered (EN) status. (Thomas, D.C., Bour, A. & Ardi, W.H., Begonia of the Matarombeo karst, Southeast Sulawesi, Indonesia, including two new species in Gardens' Bulletin Singapore 70(1): 163-176. 2018)

Etymology

  • The species epithet refers to the limestone mountain range of Matarombeonin Sulawesi Tenggara, where the type material was collected.

Notes

  • Begonia matarombeoensis is a low growing species and larger plants can form mats almost continuously covering the limestone substrate (Fig. 3A). The basal stems have relatively thick internodes, are appressed to the substrate and root at the nodes (Fig. 3B). The plants die back during drier periods and have leafless stems or only a few short-petioled, small leaves (Aurélien Bour, pers. obs.). This ecology is similar to the Sulawesian endemic Begonia siccacaudata J.Door., which is adapted to coralline limestone habitats in South Sulawesi and perennates in drier periods with leafless tuberous-rhizomatous stems. The low growth habit and ecology of Begonia matarombeoensis are unusual in the huge section Petermannia (> 400 species), but there is already known to be a considerable variety of growth habits, including several low growing prostrate-creeping species (e.g. the Sulawesian B. flacca, B. gemella Warb. ex L.B.Sm. & Wassh., B. heteroclinis Miq. ex Koord., and several Moluccan Begonia species [see Ardi et al., 2014b; Ardi & Thomas, 2015]). However, the complexly branching (paniculate-cymose), many-flowered male inflorescences, the relatively long peduncles of the female inflorescences (up to 4.2 cm long), and the relatively narrow wings (up to 5 mm at the widest point) differentiate Begonia matarombeoensis from species with a similarly low growth habit.
    The inflorescence architecture of Begonia matarombeoensis and the long peduncles of the female inflorescences are similar to those of B. siregarii Ardi & D.C.Thomas, a species growing on limestone cliffs in Southwest Sulawesi. Begonia siregarii is an erect species up to about 1 m tall, however, and also otherwise morphologically dissimilar (see Ardi et al., 2014a). (Thomas, D.C., Bour, A. & Ardi, W.H., Begonia of the Matarombeo karst, Southeast Sulawesi, Indonesia, including two new species in Gardens' Bulletin Singapore 70(1): 163-176. 2018)
  • Begonia matarombeoensis can be easily differentiated from the rest of the species in section Petermannia by its basally thickened stem with shortened internodes, the complexly branching (paniculate-cymose) and many-flowered male inflorescences, the relatively long peduncles of the female inflorescences (up to 4.2 cm long), and the recurved pedicels of the fruits (Thomas et al. 2018). Begonia matarombeoensis occupies a similar niche as B. siccacaudata Doorenboos (2000: 400) which grows on coralline limestone cliffs and limestone boulders in Southwest Sulawesi. (Ardi, W.H., Chikmawati, T., Witono, J.R. & Thomas, D.C. (2018). A synopsis of Begonia (Begoniaceae) of Southeastern Sulawesi including four new species. Phytotaxa 381.1: 027-050.)

Specimens