Begonia xenos C.W.Lin, Phonep. & Rahm, 2022

Lin, Che-Wei, Phonepaseuth, Phongphayboun & Rahm, Peter, 2022, Begonia xenos-a new species and an updated checklist of Begonia in Laos, Phytotaxa 543 (3), pp. 193-202 : 193-199

Begonia xenos C.W.Lin, Phonep. & Rahm , sp. nov.

§ Platycentrum ( Figs. 2 & 3 )

Type:— LAOS: Vientiane Province, Vang Vieng District, Tham Khanh cave , ca. 290 m elevation, 11 November 2018, C. W . Lin 712 (holotype FOF; isotypes TAIF, HAST) .

Erect or ascending herb, lithophytic or epiphytic. Stem slender, young stem scarlet red, becoming pale brown and slightly woody in appearance, internodes 2−10 mm long, 3−6 mm thick, glabrous; young plants rooting at nodes and climbing vertically up cliffs or trees. Stipules persistent, bright red, triangular to narrowly triangular, 5–15 mm long, 3.5–8 mm wide, herbaceous, strongly keeled, few fleshy red hairs fused into at the base of the keel, glabrous, margin entire, apex aristate, arista ca. 3 mm long. Leaves alternate, petiole terete, scarlet red, 4.5−10 cm long, 1.5−2.5 mm thick, glabrous; leaf blade pendent, slightly asymmetric, oblique, ovate to lanceolate-ovate, 6.5−11 cm long, 2–4.3 cm wide, broad side 1.3–2.5 cm wide, glabrous, subpeltate, apex attenuate to caudate, margin subentire or minutely and sparsely denticulate, undulate; leaf thinly coriaceous, succulent, adaxially emerald green, sometimes with silvery white semicontinuous patches or spots of variable sizes between veins; abaxially pale green; venation pinnate, midrib ca. 3 secondary veins on broad side, other primary veins branching dichotomously. Inflorescences axillary, bisexual, cymose arising directly from stem, ca. 2 orders of branching; peduncle red, 3–9 cm or longer, glabrous; bracts deciduous, pale yellow-green, ovate, elliptic to oblong, first pair ca. 7 mm long, 4 mm wide, glabrous, margin subentire to crenulate; bracts of upper inflorescence similar but smaller. Staminate flower: pedicel pale yellowish pink, 1–1.5 cm long, glabrous, tepals 4, dusky white to creamy white tinged green basally, sometimes with a slightly pinkish tinge, glabrous, margin slightly crenulate; outer 2 ovate to orbicular, 1–1.5 cm long, 1–1.4 cm wide, inner 2 elliptic to obovate, 5–9 mm long, 2–5 mm wide; androecium actinomorphic, ca. 0.3 cm across; stamens creamy yellow, 52–85; filaments fused at base; anthers narrowly obovate, ca. 1 mm long, 2-locular, apex truncate, shorter than filaments. Pistillate flower: pedicel pale yellowish pink, ca. 1.5 cm long, glabrous, tepals 5, pink, rhombic to elliptic, 6–12 mm long, 2.5–9 mm wide; ovary trigonous-ellipsoid, ca. 5 mm long, 2.5 mm thick (wings excluded), yellowish red, glabrous; 3-winged, wings unequal, reddish, glabrous, ca. 8 mm long, abaxial wing triangular, ca. 5 mm wide, lateral wings narrowly crescent-shaped, ca. 2 mm wide, margin entire; ovary 2-locular, placenta bilamellate; styles 2, fused at base, yellow, ca. 0.4 cm long, stigma spirally twisted. Capsule not seen.

Distribution and ecology:— Begonia xenos is endemic to Vang Vieng, Laos. It grows on limestone cliffs or at the entrance of semi-shady to shady, slightly moist caves, sometimes on low branches of trees in deeply shaded areas at ca. 290 m elevation.

Etymology:— From the Greek xenos , meaning ‘strange’. Most species in B. sect. Platycentrum have basifixed leaves. The epithet ‘ xenos ’ refers to the subpeltate leaves, an unusual morphological character compared to the rest of the section.

Proposed conservation status:— This species is local and scarcely endemic, while most of its populations are found from only a few limestone cliffs, with an estimated 100 mature individuals in total based on recent surveys. Based on its succulent rhizome/leaves, this species obviously has the ability to deal with the environment of secondary forests, but it only occurs in an small area of Vang Vieng. We consider an IUCN category of Endangered (EN: D) to be appropriate, considering that there are only very few individuals restricted in a single habitat, a chance event due to climate change or human impact could cause it to become Critically Endangered (CR) or Extinct (EX).

Notes:— Begonia xenos is somewhat similar with B. sinofloribunda Dorr ( Dorr, 1999) in its ascending stem, leaf shape and arrangement. Both species occur in limestone outcrops, but the new species is different in the flower number per inflorescence that is usually less than 8 (vs. more than 10), staminate flower 4-tepaled (vs. 2-tepaled) and larger outer tepals by 10–15 × 10–14 (vs. 3–8 × 3.5–9) cm, margin slightly crenulate (vs. entire), stamens 52–85 (vs. 25–31), pistillate flower 5-tepaled (vs. 2 or 3-tepaled) and 2-locular (vs. 3-locular) ovary. Moreover, B. sinofloribunda is placed in sect. Boisiana by Shui et al. (2019). Both species are very similar vegetatively, so it is reasonable to speculate that this could be an evolutionary convergence driven by the similar karst habitat of the species. Begonia xenos also resembles B. wui-senioris C.-I Peng ( Peng et al., 2014), as both are unusual among the section Platycentrum in Indochina in peltate leaves. But B. xenos is different in having a relatively erect (vs. creeping) stem, ovate to lanceolate-ovate (vs. widely ovate) leaves with a subpeltate (vs. peltate) base, glabrous lamina (vs. abaxially veins puberulous), subentire to crenulate bracts (vs. sparsely ciliate) and glabrous (vs. abaxially scabrous) outer tepals of both staminate and pistillate flowers. A comparison of the salient characters of the three species is shown in Table 1 .

Figures

FIGURE 2. Begonia xenos C.W.Lin, Phonep. & Rahm. A. Habit; B. Stipule; C, C’. Portion of leaf, upper and lower surface; D, D’. Bracts; E, E’. Staminate flower, face and side views; F, F’. Stamens, ventral and dorsal views; G, G’. Pistillate flower, face and side views; H. Cross section of ovary.

FIGURE 3. Begonia xenos C.W.Lin, Phonep. & Rahm. A, B. Habitats; C, D. Habit and habitats; E, F. Portion of leaf, upper and lower surfaces; G, H. Stipules of stem; I, J. Inflorescence, showing bracts and staminate flower, K. pistillate flower. Photos A–D, F, H by Peter Rahm; Photos E, G, I–K by Ka-Tsun Chang.