Scientific name: Begonia circularis C.-I Peng & C. W. LinEnglish name: Vietnamese name: Thu hải đường congOther name:
Herb, monoecious, rhizomatous. Rhizome stout, creeping, 1.2–2 cm thick, internodes congested, villous near the petiole insertion. Stipules deciduous, reddish, ovate-triangular, ca.1 cm long, 0.8 cm wide, strongly keeled, abaxially villous along midrib, apex aristate, arista ca. 0.5 cm long. Petioles red to reddish-green, terete, 5–9.5 (−14) cm long, 0.6–0.8 cm thick, densely pinkish villous. Leaves alternate; blade asymmetric, widely ovate to widely elliptic, 13.5–21 cm long, 9.5–17 cm wide, broad side 6–10 cm wide, basal lobes cordate, 4.8–7.5 cm, apex caudate, base strongly oblique-cordate, margin repand to denticulate, thickly chartaceous, densely magenta hispid, surface slightly rugose between veins, adaxially olive-green to dark green, embellished with a wide silvery green to lemon green ring and adorned with small similar-colored patches between primary palmate veins; abaxially reddish to pale magenta, with a ring of pale green corresponding to the pattern on adaxial surface; venation palmate with 6–8 primary veins, midrib distinct, with 2 or 3 secondary veins on each side, secondary veins branching dichotomously or nearly so, tertiary veins weakly percurrent or reticulate; all venation prominently raised and densely magenta hispid abaxially. Inflorescences axillary, dichasial cymes branched 3–5 times; peduncle 9.5–16 cm long, subglabrous; bracts and bracteoles caducous, reddish, oblong to ovate, ca. 0.8 cm long, 0.25–0.4 cm wide, boat-shaped, margin sparsely shortly fimbriate, bracteoles similar but smaller. Staminate flower: pedicel 0.9–2 cm long, tepals 4, outer 2 broadly ovate, 14–19 mm long, 13–16 mm wide, abaxially reddish, sparsely red setulose to glabrous, inner 2 oblanceolate, pinkish to white, 10–13 mm long, 2–4.5 mm wide; androecium zygomorphic, golfclub-shaped, ca. 5 mm across; stamens 45–65; anthers yellow, slightly compressed, obovate, ca. 1.3 mm long, apex retuse, filaments longer than anthers, slightly fused at base. Pistillate flower: pedicel 0.7–1 cm long, tepals 3, pinkish-white, outer 2 widely obovate to orbicular, 7–17 mm long, 8–13 mm wide, inner 1 narrowly elliptic, 5–12 mm long, 3–4 mm wide; ovary reddish, trigonous-ellipsoid, 6–10 mm long, 3–4 mm thick (wings excluded), with sparse sessile or subsessile glands, 3-winged, wings unequal, reddish-yellow, shallowly triangular, sparse subsessile-glandular, lateral wings 2–4 mm wide; abaxial wing crescent-shaped, entire, 6–10 mm wide; styles 3, fused at base, yellow, ca. 4 mm long, stigma spirally twisted. Capsule trigonous-ellipsoid, 10–17 mm long, 4–9 mm thick (wings excluded), reddish when fresh; wings unequal, shallowly triangular, lateral wings ca. 5 mm wide, abaxial wing 7–17 mm wide. Somatic chromosome number, 2n = 30.
Distribution and ecology
Endemic to Thach An District, Cao Bang Province, Vietnam (Figure 3), near the border between Vietnam and China. Growing in cracks of mossy rocks on semi-shaded limestone cliffs in evergreen broad-leaved forest, elevation ca. 600 m.
The specific epithet refers to the circular foliar variegation of the new species.
Begonia circularis somewhat resembles B. lanternaria Irmsch. and B. picturata Yan Liu, S. M. Ku & C.-I Peng (SW Guangxi, China), all members of sect. Coelocentrum, in the variegated foliage.