Begonia ducii C.H.Nguyen, T.A.Le & C.W.Lin, 2025

Nguyen, Cuong Huu, Bui, Huong Van, Le, Anh Tuan, Pham, Dien Van & Lin, Che Wei, 2025, Five new species of Begonia (Begoniaceae) from Vietnam, Phytotaxa 698 (2), pp. 82-100 : 95

5. Begonia ducii C.H.Nguyen, T.A.Le & C.W.Lin , sp. nov. § Platycentrum ( Figs. 9 & 10 )

Type:— VIETNAM. Southern Vietnam, Binh Thuan province, Tanh Linh district, Duc Phu village, primary evergreen broad-leaved forest, around point 11°17'56"N 107°41'13"E, elevation of about 550 m a.s.l., 21 October 2024, D. M.Vu VMD 211024 (holotype VNF).

Monoecious rhizomatous herb. Rhizome stout, dusky crimson to brownish-red, 3–8 cm or longer, 5–8 mm thick, internodes 1–6 mm long, hirsute and tomentose; erect stems seen only at anthesis, 1 or 2 nodes, crimson, internodes 1– 6.5 cm long, 2–6 mm thick, tomentose to villous. Stipules persistent, pale pinkish-green to yellowish-green, triangular-ovate, 5–7.5 × 3–6 mm, herbaceous, strongly keeled, abaxially densely villous-hirsute, margin minutely denticulate, apex aristate, arista ca. 3 mm long. Leaves alternate, oblique, held horizontally; petiole terete, crimson to brownish-pink tinged green, (2.5–) 7–10 cm or longer, 2–3 mm diameter, densely white tomentose or villous, glabrescent; leaf blade asymmetric, oblique, widely ovate, (5–)7.5–16 × (3–) 5–11 cm, broad side (1.5–) 3–6.5 cm wide, basal lobes cordate, (1–) 2.3–4.5 cm long, apex acuminate, margin denticulate with a line of pinkish-white hirsute; leaf chartaceous, succulent, adaxially bright green, olive green to malachite green, sometimes adorned with maroon to dark blueish-green narrow bands along all the veins, primary and secondary veins crimson; upper surface corrugated, moderately densely white hirsute, giving a wrinkled texture; abaxially pale green, densely white hirsute on all veins; venation basally ca. 8 palmate, midrib distinct, ca. 2 secondary veins on each side, other primary veins branching dichotomously or nearly so, tertiary veins reticulate; leaves of erect stem similar to terrestrial leaves but smaller. Inflorescence protandrous, terminal or axillary, bisexual, cymose panicle arising directly from rhizome or on a short stem, up to 3 orders of branching; peduncle crimson or brownish-pink tinged green, (3.5–) 6–11 cm long, extending up to 23 cm in fruiting stage, sparsely to densely white tomentose; bracts deciduous, pale green to pale pinkish-yellow, ovate to elliptic, first pair 12–15 × 6–8 mm, abaxially tomentose-hirsute, margin denticulate, ciliate; bracts of upper inflorescence similar but smaller. Staminate flower: slightly pointing downward, pedicel white tinged dusky red towards base, 20 mm long, glabrous, tepals 4, white with pale grey veins, outer 2 ovate to widely ovate, 11–15 × 9–13 mm, abaxially sparsely hirsute, inner 2 obovate, 9–15 × 5.5–10 mm, glabrous; androecium actinomorphic, ca. 4 mm across; stamens golden yellow, 50–80, filaments fused into a column to 2 mm long; anthers obovate, ca. 1 mm long, 2- locular, apex rounded, subequal or shorter than filaments. Pistillate flower: slightly pointing downward, pedicel white tinged dusky red towards base, 15–25 mm long, glabrous; tepals 5, white with pale greyish-white vein, outer 2 elliptic to widely elliptic, (10–)15–17 × (6–) 10–13 mm, glabrous or sparsely hirsute abaxially; inner 3 elliptic to oblong-elliptic, (10–)17–20 × (5–) 9–11 mm, glabrous; ovary pale green, trigonous-ellipsoid, ca. 10 mm long, 3 mm thick (wings excluded), scabrous-hirsute or hirsute; 3-winged, wings unequal, pale green, crescent-shaped, glabrous or very sparsely hirsute, lateral wings narrower, 2–4.5 mm wide, abaxial wing 7–18 mm wide, margin entire; ovary 2-locular, placenta bilamellate; styles 2, fused at base, yellow, ca. 3 mm long, stigmatic band U-shaped and spirally twisted. Capsule pedicel 2–3 cm long; ovary body trigonous-ellipsoid, 11–15 mm long, 4–6 mm thick (wings excluded); wings unequal, crescent-shaped, lateral wings ca. 4 mm wide, abaxial wing 15–22 mm wide.

Additional specimens examined:— VIETNAM. Southern Vietnam, Binh Thuan province, Tanh Linh district, Duc Phu village, primary evergreen broad-leaved forest, around point 11°21’48.5”N 107°43’16.1”E, elevation of about 500 m a.s.l., 30 December 2024, D. M.Vu VDM301224 ( VNF).

Distribution and ecology:— Begonia ducii is endemic to Binh Thuan province, southern Vietnam ( Fig. 11 ). The new species usually grows in moist shady places near waterfalls, along streams and commonly on the slopes of stream valleys in moist places covered by evergreen broad-leaved forests.

Etymology:— The specific epithet honors Mr. Vu Minh Duc, an plant enthusiast who provided material of this new species.

Conservation status:— The area of occurrence and the number of mature individuals currently cannot be correctly estimated. More field surveys are needed for assessment of its true conservation status. According to the IUCN criteria ( IUCN, 2024) it may be tentatively assessed at present as “Data Deficient” (DD).

Notes:— Begonia ducii shares similarities with B. lamdongiana Lin et al. (2021: 82) and B. mangdenensis Hoang et al. (2021: 317) , including hairy petioles, ovate leaf blades, staminate flowers with 4 tepals, and pistillate flowers with 5 tepals. However, B. ducii can be distinguished from both species by its densely corrugated upper leaf blade surface (vs. flat in B. lamdongiana and bullate in B. mangdenensis ), moderately dense white hirsute hairs on the upper leaf surface (vs. sparsely minutely scabrous in B. lamdongiana and very sparsely puberulous in B. mangdenensis ), and scabrous-hirsute ovary (vs. completely glabrous in other both species).

Figures

FIGURE 9. Begonia ducii C.H.Nguyen, T.A.Le & C.W.Lin. A. Habit; B, B'. Portion of leaf, upper and lower surfaces; C. Stipule; D. Bract; 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, dorsal and ventral views. Drawn from the holotype, VMD 211024 by Che-Wei Lin.

FIGURE 10. Begonia ducii C.H.Nguyen, T.A.Le & C.W.Lin. A–C. Habitats; D, E. Staminate flowers; F–H. Pistillate flowers; I. Cross section of an ovary; J. Capsule; K. infructescence. Photos A–D, F & K by Duc Minh Vu; photos G & J by Anh Tuan Le, photos E, H & I by Cuong Huu Nguyen of plants used for the preparation of type herbarium specimen VMD 211024 and VMD 301224.

FIGURE 11. Distribution map of Begonia quangnamensis (yellow star), B. zonata (pink circle), B. thuanchauensis (orange square), B. lii (blue triangular) and B. ducii (green hexagon) in Indochina (The map is modified from https://geocat.iucnredlist.org/editor).