Begonia laxiflora V.T.Bui, M.T.Le, Nghiem & C.W.Lin, 2024

Bui, Van Thanh, Nguyen, Khang Sinh, Le, Manh Tuan, Nghiem, Duc Trong, Uong, Sy Hung, Truong, Quang Trung, Le, Anh Tu & Lin, Che Wei, 2024, Begonia laxiflora (Begoniaceae), a new species in sect. from Central Vietnam, Phytotaxa 671 (1), pp. 98-104 : 99-103

Begonia laxiflora V.T.Bui, M.T.Le, Nghiem & C.W.Lin , sp. nov. § Petermannia ( Figs. 1 , 2 & 3 ).

Type: — VIETNAM. Quang Tri province: Dakrong distr., A Bung com., Dakrong N. R., remnants of primary evergreen broad-leaved forest on granite mountain, around point N 16.38523°, E 107.12985° (WGS 84) or X = 1812214, Y = 593741 ( VN 2000), elev. 700–900 m a.s.l. Lithophytic or terrestrial perennial herb, creeping rhizome 20–30(– 40 cm) long, young branches, leaf petiole, abaxial veins, peduncles and pedicels somewhat red, flower white to pinkish-white, capsule red, usually grown on shaded granite rocks along small streams at steep slopes in the middle to near mountain top, 25 March 2024, V. T. Bui, M. T. Le, K. S. Nguyen, D. T. Nghiem, S. H. Uong, A. T. Le, H. H. Nguyen, T.X. Loi, G. T. Anh, H. V. Che & T. B. Ho, FY24-191 (holotype: HN, isotypes: HN, HNIP, VFM, herbarium of Dakrong N. R.).

Creeping, perennial herb, monoecious. Stems crimson to brown, terete, 20–30 cm or longer, 3.5–7 mm across, simple or 2 or 3-branched, slightly thicker at nodes, glabrous or subglabrous with minute brown trichomes or glandular trichomes (microscopic examination), internodes 1.3–6 cm long. Stipules 2 at each node, ovate-triangular, slightly oblique, pale reddish-brown to dusky yellowish-green, 10–20 × 6–11 mm, abaxially subglabrous, minutely brown trichomes or glandular trichomes, keeled, margin entire, apex acuminate and cuspidate, cusp 1.5–3 mm long. Leaves alternate, oblique, held horizontally; petiole crimson to brownish-red, 3–7 cm long, 2.5–4 mm across, terete, subappressed pale brown to reddish-brown villous and minutely brown trichomes or glandular trichomes, glabrescent; leaf blade asymmetric, widely ovate, 8–15 × 5–9(–10) cm, base obliquely cordate, with a well-developed basal lobe (1–4.2 cm long) on broad side giving a cordate appearance, broad side 4–6.8 cm wide, margin denticulate, slightly revolute and undulate with rows of red puberulous and scabrescent hairs, apex acuminate to acute; leaf subcoriaceous, succulent, adaxially dusky yellowish-green to greyish-green, glabrous, waxy, abaxially pale green, veins yellowish-pink, primary and secondary veins prominently raised, densely subappressed yellowish-red villous-hirsute and minutely trichomes, minor veins puberulous; venation palmate, midrib distinct, 3 or 4 secondary veins on broad side and 2 veins on narrow side, lateral through connection between with other basal veins, tertiary (minor) veins reticulate; leaves at inflorescence branches similar to cauline ones but smaller, petiole 1.8–3 cm long, 1.5–2.5 mm across, leaf blade 3.5–8 × 2.5–5.2 cm. Inflorescence axillary and terminal, bisexual, lax cymose-paniculate, 6–12 cm long, crimson to red, erect, minutely brown trichomes or glandular trichomes, peduncle 1.7–3 cm long, sometimes with very sparsely villous-hirsute; pistillate flowers 1 or 2 on a short branches (1–15 mm) at base of inflorescence; staminate flowers only produced in distal inflorescence part, in several 3 or 4-flowered subumbellate, monochasial partial inflorescences borne on short lateral branches (6–15 mm long), at the most distal nodes sometimes reduced to a single flower. Bracts yellowish-pink to brownish-pink, hyaline, persistent; those at basal node of inflorescence in pistillate flower ovate-triangular to ovate, 7–15 × 4–7 mm, margin sparsely to densely denticulate, sometimes ciliate, apex acuminate and cuspidate; bracts at summit of inflorescence rachis with staminate flowers ovate to lanceolate, 5–12 × 2–4.5 mm, apex attenuate and cuspidate, margin denticulate and ciliate, upper bracts similar to bracts but smaller. Staminate flower: pedicel 13–17 mm long, densely minutely glandular trichomes; tepals 4, white to pinkish-white with pale greyish-pink veins, glabrous; outer 2 ovate to oblong-ovate, 14–16 × 7–12 mm, margin entire, apex acute to obtuse; inner 2 oblanceolate to narrowly oblanceolate, apex acute to obtuse, base cuneate, 8–10 × 3–4 mm; androecium zygomorphic, stamens 11–21(–27), yellow, filaments 1.0– 1.5 mm long, nearly free at base, anthers oblong-obovate, ca. 1.8 mm long, 2-locular, apex retuse. Pistillate flower: pedicel 2.5–7 mm long, with dense minutely glandular trichomes; ovary red, body trigonous-globose, 6.5–8 × 5–6.5 mm, with dense minutely glandular trichomes, 3-winged; wings equal, trapezoid to narrowly triangular, rounded to broadly acute proximally, rounded to obtuse distally, 8–10 mm long, 4–5 mm wide; ovary 3-locular, placenta bilamellate; tepals 5, pale pink with greyish-pink veins, glabrous; outer 3 or 4 tepals ovate to widely ovate, 12.5–15 × 6–11 mm; inner 1 or 2 tepals oblong-obovate, 10.5–14 × 4–6.5 mm; styles 3, orangish-red, bifid, ca. 5 mm long, apically split and Y-shaped, yellow; stigmas in a spiral band and papillose all around. Capsule pendent on a stalk ca. 1 cm long, capsule 1.1–1.5 cm long, 1.8–2.2 cm across (wings included), wings rounded proximally, pointed distally.

Distribution and ecology: — Begonia laxiflora is currently only known from its type locality, A Bung commune of Dakrong district, Quang Tri province (Central Truong Son Mountain Range). It grows on shaded granite rocks along small streams at steep slopes in the middle to near mountain top which is covered by evergreen broad-leaved forest at elevations of 700–900 meters above sea level. Within its habitat, several herbaceous and small shrubs usually found are Angiopteris helferiana C.Presl ( Marattiaceae ), Pilea sp. ( Urticaceae ), Lanonia magalonii (A.J.Hend., N.K.Ban & N.Q.Dung) A.J.Hend. & C.D.Bacon ( Arecaceae ), Curculigo annamitica Gagnep. ( Hypoxidaceae ), Acanthophippium striatum Lindl. , Nephelaphyllum tenuiflorum Blume ( Orchidaceae ), Raphiocarpus sinovietnamicus Z.B.Xin, L.X.Yuan & T.V.Do ( Gesneriaceae ), Clerodendrum sp. ( Lamiaceae ), Perilimnastes guillauminii (H.L.Li) Ying Liu ( Melastomataceae ), Ardisia harmandii Pierre ex Pit. ( Primulaceae ), Argostemma sp. , Hedyotis sp. , Mycetia tonkinensis (Pit.) Razafim. & B.Bremer , Ophiorrhiza sp. ( Rubiaceae ).

Phenology: —The plant flowers in late February, expecting until middle of March. Its dried capsules of the previous year and young fruits were observed in late February.

Etymology: —The specific epithet refers to the combination of longer stem internodes and a lax staminate inflorescence in this new species within the " B. eberhardtii complex".

Conservation status: —Our field surveys of five routes ( Fig. 3 ) stretching across the Dakrong N.R. showed that Begonia laxiflora was only found at the southernmost area of this nature reserve, bordered with A Luoi district (Thua Thien - Hue province). Approximately 200 mature individuals of this species are scattered along the small stream which is about 3 km long. Because this species only grows along the stream we estimated that its precise area of occupancy (AOO) does not exceed 10 km sq. This population has not been exploited for ornamental or medicinal purposes and its habitat is strictly protected by forest rangers of Dakrong N.R. at A Bung commune. Further work is needed to understand the full extent of occurrence (EOO) in the southern distribution areas by implementing more field surveys of A Luoi district, as well as other parts of Thua Thien - Hue province. However based on the number of individuals, the conservation status of Begonia laxiflora is preliminarily considered as Endangered (EN: D) following the IUCN Red List Categories and Criteria, version 16 ( IUCN 2024).

Notes: — Begonia laxiflora is distinguished from its three related species through several characteristics. Firstly, the inflorescence has much longer internodes than the bracts, whereas in the other three species ( B. abbreviata , B. dakrongensis and B. eberhardtii ), the internodes are hidden by the bracts. Secondly, the wings of the capsule are notably pointed at the tip, whereas they are rounded distally in B. abbreviata and B. eberhardtii . Additionally, its axillary inflorescence does not originate directly from the main stems but emerges from lateral branches, whereas in the other three species, it emerges directly from the main stems. The ovary of Begonia laxiflora appears glabrous to the naked eye, but microscopic examination reveals the surface to be covered with minute glandular trichomes. In contrast, in B. abbreviata and B. dakrongensis , it is covered with hirsute or scabrous hairs. A detailed comparison of the four species is presented in Table 1. In the distribution map presented in this study ( Fig. 3 ), three species— B. laxiflora , B. abbreviata , and B. dakrongensis —are recorded within the Dakrong Nature Reserve.

Figures

FIGURE 1. Begonia laxiflora V.T.Bui, M.T.Le, Nghiem & C.W.Lin.A. Habit; B, B'. Portion of leaf, upper and lower surfaces; C. Portion of petiole; D. Close up of petiole surface, showing subappressed villous and minutely trichomes or glandular trichomes; E. Stipule; F–F''. Bracts; F'''. Bracteolet; G, G'. Staminate flower, face and side views; H, H'. Stamens, dorsal and ventral views; I, I'. Pistillate flower, face and side views; J, J'. Style and stigmatic band, dorsal and ventral views; K. Cross section of ovary; L. Capsule.

FIGURE 2. Begonia laxiflora V.T.Bui, M.T.Le, Nghiem & C.W.Lin. A. Habitat and habit; B. Habit; C. Portion of leaf, upper surface, D, E. Lower surface of leaf sections; F. Stipules; G. Bracts; H, I. Inflorescence, also showing bracts and bracteolets; J. Staminate flowers; K. Pistillate flowers (removal of tepals); L. Cross section of ovary; M. Dried mature capsule.

FIGURE 3. Distribution map of Begonia laxiflora (yellow star), B. abbreviata (blue circle) and B. dakrongensis (red triangle) in Dakrong Nature Reserve, Dakrong district, Quang Tri province, Vietnam.