Begonia ngocbonii T.S.Hoang & C.W.Lin, 2022

Son, Hoang Thanh, Lin, Che-Wei & Bon, Trinh Ngoc, 2022, Begonia ngocbonii (sect. Petermannia, Begoniaceae), a new species from North Vietnam, Phytotaxa 541 (1), pp. 79-85 : 80-83

Begonia ngocbonii T.S.Hoang & C.W.Lin , sp. nov.

§ Petermannia. Figs. 2 & 3 .

Type:— VIETNAM: Ha Noi Capital, Ba Vi District, Ba Vi National Park , 21°4’35.02”N, 105°22’2.45”E, 723 m elev., growing on soil within primary tropical evergreen broad-leaved forests on slopes and ridges of crystalline limestone, 28 September 2018, Hoang Son 4210 (holotype: VAFS, isotype VNMN) .

Diagnosis:— In its erect stem, non-oblique leaves and axillary inflorescences, it most resembles B. pellionioides Y.M.Shui & W.H.Chen ( Wang et al. 2015: 564), but distinguishable by its hairy (vs. glabrous) stem, shorter inflorescences up to 1 cm (vs. ca. 5 cm or longer), 2-tepaled staminate and pistillate flowers (vs. 4-tepaled staminate flower and 5-tepaled pistillate flower), glabrous tepals (vs. spiny pilose on abaxial surface of outer tepals) and placenta unilamellate (vs. bilamellate).

Monoecious, erect herb. Stem erect or ascending, rooting at nodes when procumbent, pale greyish-green to reddishgreen, 30–50 cm tall, 0.3–0.7 cm across, internodes (0.5–) 1.5–8 cm long, shorter near the stem apex; sparsely to densely pale brownish strigose, hairs appressed or curved towards the apex of stem, glabrescent. Stipules creamy green to pale reddish-green, hyaline, oblong-ovate to lanceolate, 7.5–12 mm long, 3–5.5 mm wide, strongly keeled, glabrous or abaxially spares strigose at midrib, margin entire, apex aristate, arista ca. 2 mm long. Petioles terete, non-oblique, slightly grooved above, 5–10 mm long on upper stem, to 20 mm long on lower stem, ca. 2.5 mm across, pale green to reddish-green, appressed strigose. Leaves 8–14 or more, held nearly horizontally; lamina basifixed, asymmetric, obovate to narrowly obovate, 8–12 cm long (basal lobes included), 2–5.3 cm wide, broad side 1.1–2.7 cm wide, basal lobe cordate, unequal, to 5 mm long on broad side, margin sparsely denticulate with larger teeth at end of veins, apex attenuate to acuminate; leaf thickly chartaceous, succulent, slightly bullate between veins, adaxially light green to emerald green, glabrous or very sparsely red scabrous between veins, sparsely curved strigose on midrib; abaxially pale green, curved strigose on veins; venation pinnate, midrib 7.5–11.5 cm long, with ca. 4 lateral veins on each side, veins branching dichotomously, tertiary veins obscure, weakly percurrent or reticulate; midrib and primary veins reddish adaxially, red to pale brown and prominently raised abaxially. Bracts persistent, pale creamy green to reddish, ovate to ovate-triangular, basal pair ca. 2. 5 mm long, 1.5 mm wide, margin entire, apex aristate, bracts of upper inflorescence similar basal pair but smaller, reflexed. Inflorescence very short, axillary, unisexual or sometimes bisexual, pistillate flowers 1 or 2, staminate flowers 1 or few on a reduced cyme on upper stem, hidden by leaves; protogynous. Staminate flower pedicel 5–10 mm long, glabrous, tepals 2, pale pink to white, sometimes with a greenish tinge towards margin, orbicular to very widely ovate, 5–7 mm long, 7–9 mm wide, glabrous, margin entire, apex rounded; androecium actinomorphic, stamens 21–45, filaments shortly fused at base; anther obovate, ca. 0.8 mm long, apex retuse, subequal or longer than filament. Pistillate flower: subsessile, ovary pale pink to pale creamy green, trigonous-ellipsoid, ca. 6 mm long, 4 mm across excluding wings, glabrous, 3-winged, wings triangular, subequal, 7–9 mm long, ca. 3.5 mm wide, truncate distally, cuneate or rounded proximally, margin subentire, 3-locular, placenta 1 per locule; tepals 2, pinkish-white, sometimes with a greenish tinge towards margin, orbicular or very widely ovate, glabrous, 6–7 mm long, 7.5–9 mm wide, margin entire, apex rounded; styles 3, golden yellow or orangish-yellow, bifid, ca. 3 mm long, C-shaped; stigmas in a spiral band and papillose all around. Fruit subsessile, capsule pale green, ca. 10 mm long, 10 mm across (wings excluded), wings 3, subequal, triangular, margin entire, 13–15 mm long, 4–5 mm wide.

Phenology:— Flowering from September to January.

Distribution and ecology:— Currently known only from the type locality in Ba Vi National park. The species grows on soil in primary tropical evergreen broad-leaved forests, on the slopes and ridges of crystalline limestone at 650–723 meters above sea level.

Etymology: — The epithet is in honor of Mr. Trinh Ngoc Bon of the Vietnamese Academy of Forest Sciences, who is passionate about studies of Vietnamese native plants and who first discovered this new species.

Additional specimen examined (paratype): — VIETNAM. Ha Noi Capital, Ba Vi District, Ba Vi National Park , 21°4’33”N, 105°22’6”E, 658 m elev., 27 December 2016, Peng 25067 ( HAST 143990 ) .

Conservation:— Begonia ngocbonii is considered a rare species and only known from two populations in Ba Vi National Park, each with less than 250 mature individuals clustered into 50 clumps within an area of ca. 1 km 2. Field observation shows that the populations are strictly managed and protected by the staff of the Ba Vi National Park and the number of individuals has been stable for at least three decades. Following the guidelines of the IUCN Red List Categories and Criteria version 14 ( IUCN 2019), its conservation status is currently assessed as Least Concern (LC).

Notes:— Begonia ngocbonii is endemic to Ba Vi Mountain in northern Vietnam, whereas B. pellionioides is known only from SE Yunnan, China and an adjacent area of North Vietnam (Lao Kay Province). The new species is also similar to B. lamxayiana ( Souvannakhoummane 2016: 2) from Lao PDR in its cane-like habit, obovate lamina and axillary inflorescence. However, it is readily distinguished from B. lamxayiana by its congested (vs. lax) inflorescence with a few flowers (vs. many flowers), 2-tepaled staminate and pistillate flowers (vs. 4-tepaled staminate flower and 5-tepaled pistillate flower). A comparison of B. ngocbonii , B. lamxayiana and B. pellionioides is presented in Table 1 .

Figures

FIGURE 2. Begonia ngocbonii T.S.Hoang & C.W.Lin. A. Habit; B, B’. Portion of leaf adaxial and abaxial surfaces; C. Stipule; D, D’, D’’. Bracts; E, E’. Staminate flower, face and side views; F, F’. Stamens, dorsal and ventral views; G, G’. Pistillate flower, face and side views; H, H’. Style and stigmatic band, ventral and dorsal views; I. Capsule; J. Cross section of ovary.

FIGURE 3. Begonia ngocbonii T.S.Hoang & C.W.Lin.A. Habit and habitats; B. Habit; C. Portion of stem adaxial surface, also showing stipules and petioles; D. same, abaxial surface; E. Portion of leaf adaxial surface; F. Juvenile leaf, showing abaxial surface; G. Immature staminate flowers, also showing bracts; H. Staminate flowers, face view; I. Pistillate flowers, face and side views; J. Cross section of an immature capsule.