Begonia nahauensis C. H. Nguyen & C. W. Lin. A, B. Habit 2024, sp. nov.
Creators: name: Bui, Doi The
name: Nguyen, Cuong Huu
name: Tran, The Ngoc
name: Nguyen, Ly Van
name: Lin, Che Wei
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Cucurbitales
Begoniaceae
Begonia
Begonia nahauensis

description: Begonia nahauensis C.H.Nguyen & C.W.Lin, sp. nov. § Platycentrum (Figs. 1 & 2)
Type: — VIETNAM. Yen Bai province, Van Yen district, Na Hau commune, primary evergreen broad-leaved forest, at elevation 400−600 m a.s.l., occasionally along streams and on stream valley slopes in wet places with soil rich in humus, around point 21°45'28"N 104°34'26"E, rare, 18 March 2024, N. H.Cuong, B. T.Doi, T. N.The, N. V.Ly, NHC 240318012 (holotype: VNF).
Diagnosis: Begonia nahauensis resembles B. auritalata in vegetative characters, but differs in having well-developed, 3-loculed ovary (vs. one locule degenerated or very small), which are densely gland-tipped hirsute (vs. with non-glandular hairs), and the capsule has three subequal (vs. unequal), straight wings (vs. adaxial wing concave).
Cane-like herb, branching near the base, lithophytic. Stem erect or ascending, rooting at nodes and climbing vertically up cliffs; stem creamy pink to greenish-white, becoming pink olive to dusky brownish-pink with age, up to ca. 75 cm tall, 0.4–1 cm across, densely white hirsute, internodes up to 14 cm at lower part, becoming shorter (1.2–5 cm) towards the branches apex, nodes slightly swollen. Stipules semi-persistent, greenish-white, hyaline, ovate-triangular, spread to recurved, 7–13 × 5–10 mm, abaxially white hirsute, margin denticulate and fimbriate, apex aristate. Petioles terete, grooved above, up to 17 cm long at lower stems, becoming shorter (> 2.5 cm) towards the upper stems; creamy pink to greenish-white, densely white hirsute. Leaves asymmetric, oblique, held horizontally; lamina basifixed, ovate, slightly polygonal in outline, 11–21 × 5.7–13.5 cm, broad side 3.2–7.6 cm wide, basal lobes cordate, 2–4.5 cm long, chartaceous, adaxially malachite green to dark blueish-green, densely covered with small bulliform cones between veins, each cone tipped by upstanding magenta hispid setae, giving lamina a rugose appearance; abaxially magenta, pink to magenta hispid or puberulous on veins, margin denticulate and irregularly angular, sometimes with 1 or 2 shallowly triangular lobes on broadly side, with rows of magenta hispid setae, apex caudate; venation palmate, ca. 5 veins, midrib distinct, 3–5 secondary veins on each side, other primary veins branching dichotomously or nearly so, tertiary veins reticulate. Bracts hyaline, deciduous, greenish-white, ovate, boat-like, at basal node of inflorescence ca. 10 × 6.5 mm, abaxially hirsute or glandular-hirsute; bracts at the apex of inflorescence gradually smaller. Inflorescence terminal and axillary, bisexual, cymosely branching panicle 7–20 cm long, peduncle yellowish-pink to greenish-white, 5–11 cm long, densely white hirsute or glandular-hirsute, cymose with ca. 3 orders of branching, protandrous. Staminate flower: pedicel pale creamy pink to greenish-white, 4–6.3 cm long, densely white glandular-hirsute, tepals 4, white with pale grey veins, margin entire, apex obtuse to rounded; outer 2 ovate, boat-like, margin entire, 23–30 × 17–20 mm, abaxially densely white glandular-hirsute, inner 2 narrowly obovate, 14–16 × 7–9 mm, glabrous; androecium actinomorphic, ca. 8.5 mm across, stamens 90–110, filaments shortly fused at base; anthers 1.5–2 mm long, narrowly obovate to obovate, apex rounded, filaments 2–3.5 mm long. Pistillate flower: pedicel pale creamy pink to greenish-white, 2–3.6 cm long, densely white glandular-hirsute, often with 1 or 2 bracteoles (2.5–4 mm long) on middle position; tepals 5, white with pale grey veins, margin entire, apex obtuse to rounded; outer 4 ovate, oblong to widely ovate, 15–22 × 10–15 mm, abaxially white glandular-hirsute, inner 1 obovate to oblong, 14–18 × 8–10 mm, glabrous; ovary trigonous-globose, 7–10 mm across (wings excluded), greenish-white to creamy white, densely white glandular-hirsute; 3-winged, wings subequal, narrowly crescent-shaped, densely white glandular-hirsute, 11–15 mm long, 2.5–5 mm wide, margin entire; ovary 3-locular, placenta bilamellate; styles 3, yellow, ca. 7 mm long, stigma spirally twisted. Capsule trigonous-globose, ca. 15 mm × 18 mm (wings included); wings cuneate to rounded proximally, rounded distally.
Phenology: —Flowers bloom from February to April, and the fruiting period begins in March.
Vienamese name: Thu hải đường nà hẩu.
Distribution and ecology: — Begonia nahauensis is currently only known from a single forest area in Na Hau Nature Reserve (Yen Bai province, Vietnam). The new species usually grows in moist shady places near waterfalls, along streams and occasionally on the sandstone slopes covered by evergreen broad-leaved forests at elevations of 400– 600 m a.s.l. Common plants in habitats of Begonia nahauensis are Alocasia sp., Asplenium normale D.Don, Arisaema claviforme P.Bruggeman, Begonia longifolia Blume, Caryodaphnopsis tonkinensis (Lecomte) Airy Shaw, Cyathea contaminans (Wall. ex Hook.) Copel., Epipremnum pinatum (L.) Schott., Lasianthus sp., Leptomischus multiflorus Nuraliev, K.S.Nguyen & L.Wu, Myrioneuron tonkinense Pit., Musa lutea R.V.Valmayor, D.D.Lê & Häkkinen.
Etymology: —The species is named after the type locality, Na Hau Nature Reserve, in Yen Bai province, northern Vietnam.
Conservation: —The special 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 500 mature individuals growing in moist, shady places near waterfalls and along the stream. The area has thus far remained relatively undisturbed due to its significance to the surrounding village, although local people continue to collect non-wood forest products from it. Considering the small population size and fragile habitat, we propose that the new species should be preliminarily assessed as Vulnerable (VU D2) according to the IUCN criteria (2024).
Notes: —Morphologically, Begonia nahauensis closely resembles B. auritalata and B. morifolia Yu (1948: 119). These three species are entirely covered with dense hairs on stems and petioles. The leaf blades have a dark and rugose upper surface, white tepals and 3-locular ovary. A comparison of the new species with the two phenotypically similar species is presented in Table 1.
description: Published as part of Bui, Doi The, Nguyen, Cuong Huu, Tran, The Ngoc, Nguyen, Ly Van & Lin, Che Wei, 2024, Begonia nahauensis (sect. Platycentrum, Begoniaceae), a new species from northern Vietnam, pp. 115-120 in Phytotaxa 662 (1) on pages 116-119, DOI: 10.11646/phytotaxa.662.1.10, http://zenodo.org/record/14516317