Begonia yentuensis Luu & C.W. Lin, 2022

Luu, Hong Truong, Duong, Quoc Hung, Le, Khac Quyet & Lin, Che-Wei, 2022, Begonia yentuensis and B. khaucaensis (Begoniaceae), two new species from northern Vietnam, Phytotaxa 560 (2), pp. 222-232 : 223

Begonia yentuensis Luu & C.W. Lin , sp. nov. ( Figs. 1 & 2 )

Type: — VIETNAM. Bac Giang Province: Yen Tu Mountain Range, Tay Yen Tu Nature Reserve , N21°09’58” E106°46’34”, 498 m elev., 09 August 2013, Luu Hong Truong, Hoang Minh Duc, Le Khac Quyet & Duong Quoc Hung TYT22 (holotype: SGN; isotypes: SGN, PHH & TAIF) .

Monoecious tuberous herb. Stem tuberous at base, tubers globose up to ca. 3 cm with numerous fibrous roots, stemless or sometimes producing leafless erect stem to 3 cm long, ca. 5 mm across, crimson, glabrous. Stipules yellowish pink to red, very widely triangular, 2–3 mm long, 4–6 mm wide, herbaceous, abaxially strongly aristate-keeled near tip of the midrib up to 8 mm long, margin ciliate; stipules at erect stem red, triangular, ca. 3–4 × 3 mm, herbaceous, slightly keeled, glabrous, margin entire to ciliate, apex acute and mucronate. Leaves solitary, nearly appressed to substrate; petiole terete, yellowish pink, 1–7 cm long, 3–6 mm across, adaxially densely hirsute, subglabrous abaxially; leaf blades symmetric or subsymmetric, very widely ovate to orbicular, undivided or with irregular pointed shallowly lobes ca. 3–10 mm long, blade 9–23 cm long, 8.2–24 cm wide, basal lobes cordate, 1.5–5 cm long, apex acute, margin biserrate and ciliate; leaf thick chartaceous, succulent, adaxially olive green to dusky green, slightly bullate and puberulous between veins, giving lamina a wrinkled texture; abaxially magenta to brownish red, puberulous and hirsute on veins; venation palmate, midrib distinguishable, 6–18 cm long, ca. 2 major lateral veins on either side of midrib, other primary veins branching dichotomously, tertiary veins reticulate. Inflorescences terminal on erect stem or arising directly from tuber, bisexual, cymosely branching panicle 7–25 cm long, peduncle 4–12.5 cm long, branched 3–5 times, erect, red, glabrous; protandrous. Bracts deciduous, red, ovate-triangular to ovate, first pair 7–10 × 5–7 mm, glabrous, margin ciliate, bracts of upper inflorescence similar but smaller. Staminate flower: pedicel creamy pink to red, 1.3–2 cm long, glabrous, tepals 4, white to pink, glabrous; outer 2, orbicular to widely ovate, 11−13 mm across; inner 2, obovate, 9–12 mm long, 5–6.5 mm wide, apex rounded; androecium zygomorphic, ca. 3.5 mm across; stamens yellow, 17–25; filaments shortly fused at base; anthers oblong, ca. 1 mm long, 2-locular, apex rounded, filaments ca. 1 mm long. Pistillate flower: pedicel red, 0.7–2.5 cm long, glabrous, ovary pale creamy green, trigonous-ellipsoid, 8–10 mm long, ca. 5 mm thick (wings excluded), glabrous; 3-winged, wings unequal, triangular, 11–13 mm long, glabrous; lateral wings narrower, 2–4 mm wide, abaxial wing 5–7 mm wide, margin entire; ovary 3-locular, placenta undivided; tepals 5 (rarely 4), white to pink, glabrous, outer 2, orbicular, 8–12 mm across; inner 3, suborbicular to obovate, 6–11 mm long, 5–10 mm wide, apex rounded; styles 3, fused at base, yellow, 2–3 mm long, stigma spirally twisted. Capsule capsule body ca. 15 mm long, 7.5 mm across, glabrous; wings 3, unequal, 16–18 mm long, lateral wings to 5 mm wide, abaxial wing to 13 mm wide, rounded to truncate proximally, truncate distally, splitting between the locules and wings.

Distribution and ecology:— Begonia yentuensis is endemic to Bac Giang Province, North Vietnam. It is a deciduous lithophyte growing on sandstone rock under the canopy of a secondary moist tropical evergreen forest dominated by species of the Magnoliaceae , Fagaceae and Lauraceae mixed with bamboos.

Phenology:— Flowering was found in July to September and fruiting starting in August.

Etymology:— The species is named after its type locality, Yen Tu Mountain Range.

Conservation status:— Begonia yentuensis was found in western slopes of the Yen Tu Mountain Range and appears to be rare within Tay Yen Tu Nature Reserve and fewer than 100 mature individuals. It may be found in adjacent forests of the Yen Tu Mountain Range. Therefore, we provisionally propose its conservation status as Data Deficient until more information is recorded (IUCN Standards and Petitions Subcommittee, 2022).

Notes:— Begonia yentuensis resembles B. asperifolia Irmsch. (1927: 359) ( Fig. 3 ) in its winter dormant habit, subsymmetric, rugose foliage, 4-tepaled staminate flowers and pistillate flowers with 5 tepals, but it is different in its shorter petioles up to 7 (vs. to 28) cm long, androecium golfclub-shaped (vs. spherical), filaments fused at base (vs. fused at base into a column ca. 2 mm long), anthers less than 25 (vs. more than 50), apex rounded (vs. acute to mucronate) and placentae unilamellate (vs. bilamellate). Like B. asperifolia , according to phenotypic morphology and geographical origin, B. yentuensis is best placed within the group known as “unassigned to section with tubers” that belongs to Begonia subg. Platycentrum in Shui’s system. Molecular studies are necessary to confirm if there are trait combinations or new morphological traits suitable for creating a new section, or assigning the species to a known section. In the subsymmetric, solitary leaf and terminal inflorescence, B. yentuensis is also similar to B. labordei H. Léveillé (1904: 323) ( Fig. 4 ), but differs in the rugose (vs. flat) foliage, cymose inflorescence (vs. racemose at base), pistillate tepals 4 or 5 (vs. 3 or 4) and actinomorphic (vs. zygomorphic), ovary glabrous (vs. often hairy) and placentae unilamellate (vs. bilamellate). A comparison of the salient characters of the three species is presented in Table 1 .

Figures

FIGURE 1. Begonia yentuensis Luu & C.W.Lin.A. Habit; B, B’. Portion of leaf, upper and lower surfaces; C. Stipule, on top of tuber, C’. stipule on erect stem; D, D’, D”. Bracts; E, E’. Staminate flower, face and side views; F, F’, F’’. Stamens, ventral, dorsal and side views; G, G’. Pistillate flower, face and side views; H, H’. Style and stigmatic band, dorsal and ventral views; I. Capsule; J. Cross section of an immature capsule.

FIGURE 2. Begonia yentuensis Luu & C.W.Lin. A. Habit and habitat; B. Habit; C. Tuber; D. Stipules; E, F. Portion of leaf, upper and lower surfaces; G. Inflorescence; H. Staminate flowers; I. Pistillate flowers; J. Capsule; K. Cross section of an immature capsule. All photos from Luu Hong Truong et al. TYT22 by Luu Hong Truong.

FIGURE 3. Begonia asperifolia Irmsch. A, B. Habit and habitat; C. Staminate flowers; D. Pistillate flowers. A & B by Zhong-Xuan Wang, C & D by Wen-Ke Dong.

FIGURE 4. Begonia labordei H.Lév. A. Habit and habitat; B. Habit; C. Staminate flowers; D. Pistillate flowers; E. Capsules. A, D & E from Peng 20964, B from Peng 23251, C from Peng 20520 by Ching-I Peng.