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

Hoang, Thanh Son & Lin, Che-Wei, 2022, Begonia tuanii (sect. Platycentrum, Begoniaceae), a new species from Lao Cai Province, North Vietnam, Phytotaxa 567 (3), pp. 294-300 : 294-298

Begonia tuanii T.S.Hoang & C.W.Lin , sp. nov. § Platycentrum . ( Figs. 2 & 3 )

Type:— VIETNAM: Lao Cai Province, Lao Cai City, Ta Phoi Commune , 103.922273E, 22.356390N, 1,258 m elev., on the moist land and rocks in secondary broad-leaved evergreen forest, 18 February 2021, flowers and fruits, Hoang Thanh Son, Nguyen Van Tuan, 8455 (holotype VAFS; isotypes VNMN)

Plant perennial, monoecious, terrestrial. Stem erect, unbranched or little branched, yellowish-green to reddish-green, 15–25 cm tall, 5–8 mm across, covered with curved puberulous; internodes 1–5 cm long, nodes slightly swollen. Stipule decidous, ovate to elliptic, 18–23 × 8–10 mm, pale green to reddish-green, hyaline, keeled, abaxially sparsely curved puberulous, margin entire, apex cuspidate, cusp ca. 1 mm long. Petiole D-shaped, reddish-brown to pinkishgreen, grooved above, 3.5–10 cm long, 3.5–6 mm across, abaxially curved puberulous. Leaves 4–6, oblique, slightly pointing upward; lamina ovate, thinly succulent, basifixed, asymmetric, margin denticulate, crenulate to subentire, apex attenuate; lamina 13.5–27 cm long (basal lobes included), 7.3–14.2 cm wide, broadside 4.8–9.5 cm wide, base unequal, basal lobes cordate on broadside, 2.2–4 cm long, adaxially olive green to dusky green with reddish veins, very sparsely scabridulous between veins; abaxially magenta to pale green tinged red, densely curved puberulous on veins; venation palmate-pinnate, midrib distinguishable, 7.7–22.5 cm long, ca. 3 major lateral veins on either side of midrib, other primary veins branching dichotomously, minor veins reticulate. Bract decidous, pale yellowish-green to dusky red, hyaline, those at basal node of inflorescence ovate to elliptic, to 1.8 × 0.8 cm, apex obtuse, sometimes with a short apiculate, margin entire to sparsely denticulate or puberulous; bracts at summit of inflorescence similar but smaller. Inflorescence axillary in upper leaf axils, bisexual, cymosely branching panicle 10–15 cm long, peduncle crimson to pinkish-green, ca. 5.5 cm long, ca. 2 orders of branching, erect or ascending, glabrous, protandrous. Staminate flower: pedicel pink to yellowish-pink, 3.2–5 cm long, glabrous, tepals 4, white to pale pink, glabrous; outer 2 widely ovate, margin entire, 2.5–4 × 2.4–3.5 cm, inner 2 elliptic to obovate, 2–3.5 × 1–2 cm; androecium actinomorphic, stamens 90–120, filaments fused into a column to 5 mm long; anthers 1.5–2 mm long, widely obovate, apex rounded or truncate, filaments 2–4 mm long. Pistillate flower: pedicel pinkish-green to red, ca. 4.5 cm long, sometimes with a pairs alternate ovate bracteoles ca. 1 × 0.7 cm; tepals 5, white to pinkish-white, glabrous, outer 4 tepals larger, suborbicular to widely obovate, 1.5–2.5 × 1.5–2.7 cm, inner 1 tepal obovate, 1.5–2.2 × 1–1.4 cm; ovary green to reddish-green, body trigonous-ellipsoid, ca. 1.5 cm long, 1.2 cm across, sparsely verrucose, 3-winged; wings red to green, subsequal, abaxial wing slightly wide than lateral ones, very narrowly crescent-shaped, ca. 20 × 2–5 mm, margin entire, verrucose; ovary 3-locular, placenta bilamellated; styles 3, greenish-yellow, bifid, deeply divided to base, Y-shaped, ca. 7 mm long; stigmas in a spiral band and papillose all around. Capsule (immature) pendent on a stalk, tepals caducous, capsule ca. 15 mm long, 20 mm thick (wings included), slightly fleshy, wings unequal, very narrowly crescent-shaped, rounded to obtuse proximally, rounded distally.

Distribution and ecology:— For now, Begonia tuanii is known only from Ta Phoi Commune, Lao Cai City, Lao Cai Province and its vicinity. The new species grows on humid lands in the secondary broad-leaved evergreen forest at elevations of ca. 1,258 m, together with Urticaceae ( Elatostema sp. ), Polygonaceae ( Polygonum sp. ), and Balsaminaceae (Impetiens sp.), Begoniaceae ( Begonia handelii Irmsch. ) and Selaginellaceae ( Selaginella sp. ).

Etymology:— The specific epithet is named in honor of Mr. Nguyen Van Tuan of the Silviculture Research Institute (SRI), who first collected the type specimens of this new species.

Proposed conservation status:— Currently, Begonia tuanii is only found in the Ta Phoi Commune which is likely to represent its full natural range. This new species has quite a narrow distribution that is not included in any protected forest, with only two known populations of fewer than 30 individuals. We consider an IUCN category of Endangered (EN D) to be appropriate ( IUCN Standards and Petitions Subcommittee, 2019).

Notes:— Like Begonia fordii Irmsch. (1939: 501) , B. tuanii has erect stem, ovate leaves and axillary inflorescence with 4-tepaled staminate flowers and 5-tepaled pistillate flower with 3-locular ovaries, however, both species are different in many respects (see Table 1 ). Among the begonias of B. sect. Platycentrum in Vietnam, B. tuanii is also somewhat similar with B. wenshanensis C.M.Hu ex C.Y.Wu & T.C.Ku (1995: 262) ( Fig. 4 ), but the new species can be easily told apart from B. wenshanensis by its shorter height, pistillate flowers with 5 tepals (vs. 3) and abaxial wing very narrowly crescent-shaped (vs. narrowly triangular or falcate). In addition, the new species also resembles B. hymenocarpa C.Y. Wu (1995: 256) in vegetative characters, both have erect cane-like habit, ovate leaves, axillary inflorescence and 3-loculate ovary with the placentation axile and bilamellate placentae. However, it is clearly distinct from B. hymenocarpa in its larger leaves and tepals, glabrous staminate flowers and slightly fleshy capsule. A comparison of the salient characters of the four species is presented in Table 1 .

Figures

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

FIGURE 3. Begonia tuanii T.S.Hoang & C.W.Lin. A, B. Habit and habitat; C. Leaf, upper and lower views; D. Portion of leaf, upper surface, E. same, lower surface; F. Inflorescence; G. Stipule, also showing stem and petioles; H. Immature inflorescence, also showing bracts; I. Staminate flowers; J. Androecium; K. Pistillate flower; L. Cross section of ovary. All photos from by Hoang Thanh Son.

FIGURE 4. Begonia wenshanensis C.M.Hu ex C.Y.Wu & T.C.Ku. A, B. Habits; C. Immature inflorescence, also showing bracts; D. Inflorescence; E. Staminate flowers, face and side views; F. Pistillate flower. All photos from Peng 20516 by C.-I Peng.