Begonia rigidifolia Aver. ssp. sonhungii C.W.Lin, 2021

Lin, Che-Wei, Phan, Luong-Cong-Son & Nguyen, Ngoc-Hung, 2021, Begonia rigidifolia ssp. sonhungii (sect. Petermannia, Begoniaceae), a new subspecies from limestone hills in Central Vietnam, Phytotaxa 498 (2), pp. 139-144 : 139-143

Begonia rigidifolia Aver. ssp. sonhungii C.W.Lin ssp. nov. —

TYPE: VIETNAM. Thua Thien Hue province, Nam Dong district, Thuong Quang town, elev. 600–800 m, 22 October 2020, C.W.Lin 714 (holotype, SGN ; isotype, TAIF ) Figs. 2 , 3

Monoecious rhizomatous herb. Rhizome stout, reddish, creeping and elongate, 0.7 − 1.1 cm thick, internodes congested, hirsute. Stipules persistent, reddish-green, widely triangular-ovate, 6.5–10 × 7–12 mm, herbaceous, strongly keeled, abaxially hirsute at midrib, margin entire, apex long aristate, arista 7 − 13 mm long. Leaves alternate, petiole terete, dusky rose pink to vermilion, 6.3 − 13.5 cm long, 2.5 − 3.5 mm thick, sparsely white villous, glabrescent; leaf blade asymmetric, oblique, widely ovate to suborbicular, peltate, 7.2 − 12.5 × 5–9 cm, broad side 3–5.2 cm wide, apex acuminate, margin denticulate and puberulous; leaf coriacellate to coriaceous, succulent, adaxially olive green to dark viridian, sometimes with a maroon tinge, embellished with a wide pale green ring and adorned with small similarcolored dots between the primary palmate veins, and a narrow ring along the margin, surface very sparsely puberulous; abaxially purplish to magenta, with a ring of pale green corresponding to the pattern on adaxial surface, hirsute on all veins, glabrescent; venation basally ca. 8 palmate, midrib distinct, ca. 2 secondary veins on each side, secondary veins branching dichotomously or nearly so, tertiary veins weakly percurrent or reticulate. Inflorescences axillary, dichasial cymes, arising directly from rhizome, branched 3 or 4 times; peduncle dusky rose pink to vermilion, 10–18 cm long, densely minutely tomentose (microscopic examination), sometimes very sparsely hirsute, glabrescent; bracts dusky rose pink to creamy green, ovate to widely ovate, first pair ca. 7 mm across, glabrous, margin fimbriate, bracts of upper inflorescence similar but smaller. Staminate flower: pedicel (0.4–) 1.4–2.2 cm long, minutely tomentose (microscopic examination), tepals 4, creamy white, glabrous, outer 2 suborbicular, ca. 8 mm across, inner 2 obovate to elliptic, ca. 5 × 3 mm; androecium actinomorphic, ca. 4 mm across; stamens golden yellow, 25–55; filaments shortly fused at base; anthers widely obovate, ca. 1 mm long, 2-locular, apex retuse, subequal at filaments. Pistillate flower: pedicel 0.7–1.3 cm long, minutely tomentose (microscopic examination), tepals 3, glabrous, creamy white, outer 2 suborbicular to depressed ovate, 5–8 mm × 7–10 mm, inner 1 elliptic, ca. 4 × 2 mm; ovary trigonous-ellipsoid, 5–7 × 2.5–3 mm (wings excluded), white to pinkish; 3-winged, wings unequal, pinkish, 7–10 mm long, lateral wings narrower, narrowly crescent-shaped, 2–3 mm wide, abaxial wing crescent-shaped, ca. 5 mm wide, margin entire; ovary 3-locular, placenta bilamellate; styles 3, fused at base, golden yellow, ca. 3 mm long, stigma spirally twisted. Capsule tepals usually persistent; capsule trigonous-ellipsoid, 8–10 × ca. 5 mm (wings excluded), greenish or pinkish when fresh; wings unequal, lateral wings ca. 3 mm wide, abaxial wing crescent-shaped, 6–10 mm wide.

Distribution and ecology: Begonia rigidifolia ssp. sonhungii is endemic to Nam Dong district, Thua Thien Hue province, Vietnam. On semi-shaded cliff faces or steep limestone slopes in evergreen broad-leaved forest, at 600–800 m elevation.

Etymology: Named in honor of Phan Luong Cong Son and Nguyen Ngoc Hung, by adapting the last part of their name. They are two amateur enthusiast who first discovered this new subspecies.

Notes: Begonia rigidifolia ssp. sonhungii is similar to B. rigidifolia ssp. rigidifolia ( Averyanov & Nguyen, 2012) , as both taxa have peltate and coriacellate leaves that are variegated, staminate flowers with 4 tepals and pistillate flower with 3 tepals. Geographically, both species occur in Central Vietnam. However, B. rigidifolia ssp. sonhungii can be distinguished from B. rigidifolia ssp. rigidifolia by having both lamina surfaces puberulous or hirsute (vs. glabrous), lamina adaxial surface variegated with a light-colored band and dots that have distinct boundaries (vs. irregular, radiantly arranged dark-colored spots with obscure boundaries), stamens widely obovate (vs. obovate) and capsules with a wider abaxial wing (6–10 mm vs. 2–3 mm). Another Vietnamese species, Begonia vietnamensis also has fleshy peltate leaves, but the new taxon differs in having hairy (vs. glabrous) petiole and leaves, bracts margin fimbriate (vs. entire) and pistillate flower 3-tepaled (vs. 2-tepaled).A detailed comparison of the three taxa is presented in Table 1 .

Figures

FIGURE 2. Begonia rigidifolia ssp. sonhungii C.W.Lin from Lin 714. A. Habit; B, B’. Portion of leaf abaxial and adaxial surfaces, also showing leaf margin; C. Stipule; 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 3. Begonia rigidifolia ssp. sonhungii C.W.Lin from Lin 714. A, B, C. Habit and habitats, showing inflorescence and infructescence; D, E. Portion of leaf, adaxial and abaxial surfaces; F. Rhizome, showing stipules; G. Inflorescence, showing staminate and pistillate flowers.