Begonia khaucaensis 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 : 227-230

Begonia khaucaensis Luu & C.W.Lin , sp. nov. ( Figs. 5 & 6 )

Type:— VIETNAM. Ha Giang Province: Dong Van Karst Plateau - Du Gia National Park, Khau Ca Forest , 22°50’54”N 105°7’16”E, 800m elev., 22 October 2016, Luu Hong Truong & Le Khac Quyet HG 6 (holotype: SGN; isotypes: SGN, PHH & TAIF) .

Monoecious rhizomatous herb. Rhizome stout, creeping, crimson, ca. 1 cm thick, internodes 0.5–3 cm long, hirsute. Stipules crimson to reddish olive green, widely triangular, 1.5–2.5 cm long, 1.2–2.3 cm wide, herbaceous, keeled, abaxial midrib scattered with white hirsute, margin entire, apex aristate, arista ca. 3 mm long. Leaves alternate, petiole terete, crimson to dark brownish red, 18–30 cm long, 0.5–1 cm thick, lenticels slightly prominent, creamy white, sparsely to densely hirsute, glabrescent; leaf blade asymmetric, suborbicular to reniform, oblique, with a welldeveloped basal lobe on one side giving a cordate appearance, 17.5−27 cm long, 15–23 cm wide, broad side 9.5–16 cm wide, basal lobes cordate, 5–11 cm long, margin sparsely denticulate to subentire, apex acuminate; leaf thin coriaceous, succulent, adaxially emerald green (vermilion to greenish maroon when juvenile), sparsely bullate between veins, bulla tipped white hirsute, glabrescent; abaxially pale green, veins pale red; venation basally 7–9 palmate, midrib distinct, ca. 2 secondary veins on each side, lateral through connection between with other basal veins, minor veins reticulate. Inflorescences axillary, dichasial cymes, arising directly from rhizome, branched up to 5 times; bisexual, cymosely branching panicle 16–30 cm long, peduncle olive green to crimson, 13–25 cm long, glabrous. Bracts white to rosy red, orbicular to very widely ovate, first pair up to 2.5 cm across, glabrous, margin entire, apex retuse to rounded or apiculate; bracts of upper inflorescence similar but smaller. Staminate flower: pedicel white to pink, 0.8–2 cm long, glabrous; tepals 4, white to rosy pink, glabrous; outer 2, very widely obovate to orbicular, 12–15 mm long, 13–16 mm wide; inner 2, elliptic, ca. 7 mm long, 3 mm wide; androecium zygomorphic, ca. 5 mm across; stamens golden yellow, 40–65, filaments fused at base, anthers narrowly obovate-triangular, ca. 1.5 mm long, 2-locular, apex truncate to slightly retuse, shorter than filaments. Pistillate flower: pedicel pinkish white to rosy pink, 1.7–2 cm long, glabrous; tepals 3, rosy pink to white, glabrous; outer 2, orbicular to widely depressed ovate, 9–14 mm long, 8–15 mm wide; inner 1, elliptic, 5–8 mm long, 2–3 mm wide; ovary narrowly trigonous-ellipsoid, 6–8 mm long, ca. 3 mm thick (wings excluded), pink to white, 3-winged; wings unequal, pinkish white, 8–10 mm long, lateral wings narrower, narrowly crescent-shaped, 1.5–2.5 mm wide, abaxial wing crescent-shaped, ca. 4 mm wide, margin entire; ovary 3-locular, placenta bilamellate; styles 3, fused at base, golden yellow, ca. 3.5 mm long, stigma spirally twisted. Capsule pendent on a stalk 28–37 mm long, tepals persistent, capsule ca. 15 mm long, 1 cm thick (wings included), wings unequal, crescent-shaped, rounded to cuneate proximally, rounded distally.

Distribution and ecology:— Endemic to Du Gia National Park in Ha Giang Province. The new species is an evergreen lithophyte growing on damp limestone rock under the canopy of tropical evergreen forests dominated by Burretiodendron hsienmu W.Y.Chun & F.C.How (Malvaceae) and species of the Clusiaceae , Sapindaceae , Ebenaceae , Euphorbiaceae , Aceraceae , Araliaceae and Fagaceae .

Phenology:— Flowering was seen in October and November, and fruiting starting in November.

Etymology:— The species is named after its type locality, Khau Ca Forest.

Conservation status:— Least Concern (LC) (IUCN Standards and Petitions Subcommittee, 2022). Begonia khaucaensis appears to be abundant and well protected within the Khau Ca Forest of Dong Van Karst Plateau - Du Gia National Park. No threats to its existence were seen.

Notes:— B. khaucaensis is restricted to limestone regions, and it has characters such as rhizomatous habit, axillary inflorescence and 3-tepaled pistillate flowers. These characters are shared by sect. Coelocentrum , however, it is also similar with the broad delimitation of sect. Petermannia in Shui’s system (2019) in many aspects. We are unable to appropriately allocate this new species to any section until molecular information is available. Begonia khaucaensis somewhat resembles B. jubar V.T.Pham & C.W. Lin (2021: 145) in its rhizomatous habit, 4-tepaled staminate flowers and 3-tepaled pistillate flowers with 3-locular ovaries with blamellate placentae, but it is different from B. jubar in its hairy stipules (vs. glabrous), sparsely to densely hirsute petioles (vs. glabrous), suborbicular to reniform leaves (vs. ovate to widely ovate with slightly polygonal outline), entire bract margins (vs. denticulate to serrate with very short soft hairs), zygomorphic androecium (vs. actinomorphic or nearly so) and crescent-shaped ovary wings (vs. triangular). Moreover, B. khaucaensis bears some resemblance to B. quadripetiolata Aver. & H.Q.Nguyen (2019: 135) in the rhizomatous habit, uniformly green leaves, 4-tepaled staminate flowers and the bilamellate placentae, however, the new species markedly differs in the petioles have a terete outline (vs. quadrate), leaf upperside very sparsely hirsute hairs (vs. glabrous), zygomorphic (vs. actinomorphic) androecium and 3-tepaled (vs. 5-tepaled) pistillate flowers. A detailed comparison of B. khaucaensis with these two phenetically similar species are presented in Table 2 .

Figures

FIGURE 5. Begonia khaucaensis Luu & C.W.Lin. A. Habit; B, B’. Portion of leaf, upper and lower surfaces; C. Stipule; D, D’, D’’. Bracts; E, E’. Staminate flower, face and side views; F, F’. Stamens, ventral and dorsal 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 6. Begonia khaucaensis Luu & C.W.Lin. A, B. Habit and habitat; C. Young leaf, also showing petioles; D. Inflorescence; E. Inflorescence branch, showing bracts; F. Staminate flower, face and back views; G. Pistillate flower, face and side views; H. Capsule; I. Cross section of ovary.All photos from Luu Hong Truong & Le Khac Quyet HG6 by Luu Hong Truong.