The new species is similar to B. hahiepiana H.Q. Nguyen & Tebbitt in broadly ovate asymmetric leaves with slightly truncate or round apex and the corned berry fruit, but different from it in the broadly ovate or rotund leaves (vs. ovate), almost flat adaxial surface of leaves (vs. puckered), glabrous outer surface of petals (vs. with red trichomes), 4-loculed and glabrous berry fruit covered by dense white spots (vs. 3-loculed and pubescent fruit covered by the lax white spots).

VIETNAM. Phu Tho Province, Xuan Son county, Xuan Son National Park, 21°07’05”N, 104°57’09”E, 478 m a.s.l., 8 April 2016, Y.M. Shui, W.H. Chen, C. Liu, H.Q. Nguyen, H.T. Nguyen, N.Q. Chuong CK 0916 (holotype, KUN!; isotype, CPC!=Herbarium of the Centre for Plant Conservation, Vietnam Union of Science and Technology Associations, Hanoi).

Rhizome: 4–6 cm long, 0.5–1 cm in diam. Stipule pale brown to reddish, triangular, glabrous, 0.7–1 cm × 0.2–0.4 cm, margin entire, apex acuminate. Leaves: petiole terete, 7.5–11 cm long, 1–2 mm in diam., densely covered by red lanes; blade greenish, asymmetric, broadly ovate or rotund, 8–14 × 6.5–9 cm; base cordate; apex subacute to obtuse; margin denticulate, short ciliate; adaxially greenish, almost flat, slightly glabrous and extremely sparely strigillose between secondary veins; abaxially red, veins densely red pubescent; venation palmate, 5–6 primary veins, secondary veins brunching dichotomous, tertiary veins reticulate. Inflorescence: dichasial cyme, peduncle erect, 6–9 cm long, red or brownish villous; bracts caducous, triangular to lanceolate, reddish, 5–7 × 2–3 mm, apex acuminate, margin entire. Staminate flower: pedicels 0.5–1.5 cm long; tepals 4, white, adaxially subglabrous, abaxially glabrous; outer tepals 2, broadly ovate, 0.7–1.5 × 0.6–1.2 cm; inner tepals 2, white, oblanceolate to oblong, 0.8–1.6 × 0.2–0.5 cm, base cuneate to rounded, apex acute to obtuse, margin entire; androecium actinomorphic, stamens numerous; filaments fused at base; anthers yellow, obovate, 1–1.2 mm long, apex convex, shorter than filaments, with longitudinal slits. Pistillate flower: pedicel 0.4–0.7 cm long; tepals 5, white; outer tepals 3, broadly ovate, 0.8–1.2 × 0.4–0.6 cm, apex obtuse to rounded, margin entire; inner tepals 2, ovate, 0.5–0.7 × 0.4–0.6 cm, apex obtuse to rounded, margin entire; styles 3, free; stigmas bifid with twisted bands; ovary reddish, 0.2–0.3 cm long, 0.2–0.4 cm in diam., with white papillose and 4 thickened corns; placentation axile, 4-loculed, placentae 2 each locule. Fruit berrylike, white papillose, wingless and with 4 thickened rib-like horns.

Flowering in April–May, fruiting in April–June.

The epithet refers to the white spots on the fruit surface.

The species only grows in deep ground amongst rocks in limestone forests.

The species occurs exclusively in Phu Tho Province, Xuan Son country, Xuan Son National Park of Vietnam.

VIETNAM. Phu Tho Province, Xuan Son county, Xuan Son National Park, 21°07’01”N, 104°57’29”E, 438 m a.s.l., 8 April, 2016, Y.M. Shui, W.H. Chen, C. Liu, H.Q. Nguyen, H. T. Nguyen, N. Q. Chuong CK 0918 (KUN, CPC).

Currently six species from section Sphenanthera are recognised as occurring in Vietnam: Begonia acetosella Craib, B. balansana Gagnep., B. handelii Irmscher, B. longifolia Blume, B. ceratocarpa S.H. Huang & Y.M. Shui and B. hahiepiana H.Q. Nguyen & Tebbitt. Although this new species grows together with B. hahiepiana, it is easily distinguished by the glabrous and 4-loculed berry fruit, which has been discussed in the above diagnostic description. Within the Vietnamese species of the section, the stemless habit, the narrow inflorescence and the small horned appendage of the berry fruit indicate that the new species is also similar to Begonia ceratocarpa and B. balansana. The detailed comparison reveals that it is more similar to B. ceratocarpa with 3–4-loculed fruits than B. balansana with 6–7-loculed fruit. It is different from B. ceratocarpa in the broadly ovate or rotund leaves (vs. ovate), the unlobed leaf blade (vs. slightly lobed), round leaf top (vs. acuminate leaf top), petioles with red pubes (vs. with brown 1anes), 5 female tepals (vs. 3), densely white-spotted surface of berry fruit (vs. sparely spotted), truncate fruit top without a beak (vs. an acute fruit top with a beak).