Begonia quangnamensis C.H.Nguyen, V.H.Bui & 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 : 83-86

1. Begonia quangnamensis C.H.Nguyen, V.H.Bui & C.W.Lin , sp. nov. § Platycentrum ( Figs. 1 & 2 )

Type:— VIETNAM. Central Vietnam, Quang Nam province, Tay Giang district, A Tieng village , secondary evergreen broadleaved forest, occasionally on the slopes of stream valleys in moist places with soil rich in humus, around point 15°54'25"N, 107°29'54"E, elevation of about 600 m a.s.l., 08 September 2024, V. H.Bui BVHQN80924 (holotype VNMN; isotype VNF) .

Monoecious herb, rhizomatous initially and becoming stoloniferous. Rhizome creeping, maroon to purplish-red, 6–9 mm thick, internodes up to 6 cm long, scattered with white to pale reddish-brown retrorse hirsute; aerial stems seen only at anthesis, usually 1 node, internodes ca. 15 cm long, 4–5.5 mm thick, very sparsely retrorse hirsute. Stipules persistent, maroon to purplish-red, triangular, 8–12 × 5–7 mm, herbaceous, strongly keeled, adaxially hirsute or villous along midrib, margin entire or sparsely denticulate with fimbriate, apex aristate, arista up to 5 mm long. Leaves alternate, oblique, slightly pointing upward; petiole terete, maroon to purplish-red, 15–30 cm long, 4–5.5 mm diameter, densely white to pinkish-brown retrorse hirsute or retrorse appressed-hirsute; leaf blade asymmetric, oblique, ovate to lanceolate-ovate, 13.5–21.5 × 5.5–9 cm, broad side 3.5–5 cm wide, basal lobes cordate, 1.3–1.8 cm long, apex short caudate, margin subentire to crenate, slightly recurved with a line of hirsute; leaf thick chartaceous to thinly coriaceous, succulent, adaxially dark blueish-green to olive green tinged brownish-red, glabrous, waxy, with moderately densely minutely depressed dots, rugose-bullate, giving a strongly wrinkled texture; abaxially pale purplish-green to magenta; venation palmate-pinnate, midrib distinct, ca. 3 secondary veins on each side, other primary veins branching dichotomously or nearly so, tertiary veins reticulate; major veins crimson or reddish-green adaxially, all veins purplish-red and scattered with hirsute-villous abaxially; leaves of erect stem similar to terrestrial leaves but smaller. Inflorescence protandrous, axillary, cymose arising directly from the rhizome or on an erect stem, 2 or 3 orders of branching; peduncle 7.5–11.5 cm long, purplish-red, erect, pale reddish-brown retrorse hirsute, sometimes subglabrous; bracts crimson to greenish-red, hyaline, semi-persistent, ovate, first pair 5–7 × 3.5–4 mm, decreasing in size towards the more distal inflorescence nodes, abaxially hirsute, margin fimbriate, acute and aristate at apex, arista ca. 1 mm long. Staminate flower: pedicel brownish-pink, ca. 17 mm long, sparsely hirsute; tepals 4, outer 2 pinkish-white with pale greyish-pink veins, widely ovate, 17–20 × 18–19 mm, margin entire, abaxially white to pink hirsute; inner 2 white or pinkish-white, widely obovate to suborbicular, apex round, base cuneate, 15–16 × 13–14 mm, glabrous; androecium actinomorphic, ca. 6 mm diameter; stamens ca. 70, yellow, filaments free, ca. 1.8 mm long, anthers obovate, ca. 1.5 mm long, 2-locular, apex obtuse to rounded. Pistillate flower: not seen. Capsule pedicel ca. 3 cm long, very sparsely hirsute to subglabrous; ovary body trigonous-ellipsoid, 2-locular, 14–16 mm long, 5–6 mm thick (wings excluded), subglabrous; wings unequal, crescent-shaped, lateral wings ca. 6 mm wide, abaxial wing 17–22 mm wide.

Additional specimens examined: — VIETNAM. Quang Nam province: Tay Giang district, A Xan village, primary evergreen broad-leaved forest, around point 15°81'58"N, 107°33'06"E, elevation of about 1,300 m a.s.l., 20 April 2022, C. H. Nguyen, K. S. Nguyen, H.X. Cao, CKH 2022042079 ( VNF).

Distribution and ecology:— Begonia quangnamensis is currently only known from a single forest area in A Tieng and A Xan commune, Tay Giang district, Quang Nam province, central Vietnam ( Fig. 11 ). The new species usually grows in moist shady places near waterfalls, along streams and occasionally on the slopes of stream valleys in moist places with soil rich in humus covered by evergreen broad-leaved forests at elevations of 600–1,300 m a.s.l. Flowers in August–October.

Etymology:— The specific epithet is derived from Quang Nam province, the type locality of this new species.

Conservation status:— The field studies conducted around the type location revealed no other populations outside the estimated occupancy area of approximately 5 km ². The type location comprises approximately 100 mature individuals growing in moist, shady places near waterfalls and along the stream. Given the small population size and the ongoing threats from road construction and agricultural expansion, which have led to the degradation of this fragile habitat, we propose that the new species should be preliminarily assessed as Critically Endangered (CR B1a,b(iii)2a+C1) according to the IUCN criteria (2024).

Notes:— Based on the observed morphological characteristics, such as a rhizomatous habit, anthers with a rounded apex, fruit with an enlarged adaxial wing, and a 2-loculed ovary, we propose placing this species within sect. Platycentrum . Begonia quangnamensis can be distinguished by its rhizomes with elongate stolons, long-petioled leaves with a wrinkled texture that often appear slightly upward-pointing, and petioles covered in retrorse appressed hairs. This combination of characters is unique among the known begonias of Indochina. The new species somewhat similar to B. hongiaoensis Lin et al. (2021: 78) , sharing the stoloniferous habit, long-petioled ovate leaves, and actinomorphic androecium in the staminate flowers. However, B. quangnamensis is distinguished by several key morphological differences: its petioles are covered in retrorse appressed-hirsute hairs (vs. minutely appressed-tomentose in B. hongiaoensis ), leaf blade rugose-bullate (vs. flat), hirsute-villous on all veins of abaxial surface (vs. sparsely appressed tomentose, glabrescent), and tepals of staminate flowers hirsute (vs. glabrous) on the outside.

A recently described species from Myanmar, B. persistens Maw et al. (2021: 215) , shares several characteristics with B. quangnamensis , such as upward-pointing ovate foliage and 4-tepaled staminate flowers with an actinomorphic androecium. Nonetheless, these two species are readily distinguishable: B. quangnamensis has longer petioles 21–30 cm (vs. 9–15 cm) long, terete (vs. narrowly winged on both sides), and covered in retrorse appressed-hirsute (vs. densely to sparsely tomentose), leaf blade lower side hirsute-villous on all veins (vs. tomentose), retrorse appressed-hirsute (vs. tomentose) peduncle, and smaller outer tepals of the staminate flowers, measuring 17–20 × 18–19 mm (vs. 12–13 mm) across.

Figures

FIGURE 1. Begonia quangnamensis C.H.Nguyen, V.H.Bui & C.W.Lin. A. Habit; B, B'. Portion of leaf, upper and lower surfaces; C. Stipule; D, D'. Bracts; E. Portion of petiole; F, F'. Staminate flower, face and side views; G–G'''. Stamens, ventral, side and dorsal views. Drawn from the holotype, BVHQN80924 by Che-Wei Lin.

FIGURE 2. Begonia quangnamensis C.H.Nguyen, V.H.Bui & C.W.Lin. A, B. Habitats; C. Habits; D. Rhizome, also showing stipules, petioles and peduncle; E, F. Portion of leaf, upper and lower surfaces; G. Leaf, upper and lower surfaces; H. Portion of petiole; I. Inflorescence; J. Staminate flower, face and back views; K. Capsules. Photos A, B, C(right) & K by Cuong Huu Nguyen; Photos C(left)–J by Huong Van Bui of plants used for the preparation of type herbarium specimen BVHQN80924.

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).