The new species is similar to Begonia longicarpa K.Y. Guan et D. K. Tian in the clavate berry fruit, but differs from it in its hispid petiole (vs. pubescent), five female petals (vs. three) and short segments of placentation per locule (vs. long segments).

VIETNAM. Tuyen Quang province, Lam Binh district, Thuong Lam community, in the secondary tropical evergreen lowland rainforest and broad-leaved forests on the slopes and ridge of crystalline limestone hills with highly eroded earth, grow on ground soil, male and female flowers white, fruit berry, green or pink, 22°30'05"N, 105°18'11"E, 484 m a.s.l., 11 October 2017, H.Q. Nguyen,H.T. Nguyen, K. S. Nguyen, N.Q. Chuong CPC 8463 (holotype, KUN!; isotype, CPC!).

Rhizome: 3–5 cm long, 1.0–1.7 cm in diam. Stipule triangular, 0.8–1×0.2–0.4 cm, pale brown to reddish, margin entire, apex acuminate, adaxially glabrous, abaxially red hirsute. Leaves all basal, alternate; petiole terete, 9–15 cm long, 2–5 mm in diam., densely reddish hirsute; blade dark green or brown, asymmetric, broadly ovate, 7–14× 3.5–9.0 cm, base cordate, oblique, apex subacute to obtuse, margin denticulate, short ciliate, adaxially dark green, almost glabrous, usually with white spots, abaxially dark red, densely red lanate on veins; venation palmate, 6–7 primary veins, secondary veins brunching dichotomous, tertiary veins obviously reticulate, densely velutinous on veins. Inflorescence dischasial cyme, axillary, peduncle 3–5 cm, erect, red to brownish villous; bracts pale greenish, triangular to lanceolate, 1–1.5× 2–3 mm, margin dentate and ciliate, apex acuminate. Staminate flower: pedicel 2.2–3.5 cm, glabrous above the middle, villous below the middle; tepals 4, white-pinkish, glabrous; outer tepals 2, ovate, 1.2–1.5× 0.6–1 cm, apex acute, base cuneate, margin entire; inner tepals 2, oblanceolate to oblong, white-pinkish, 0.8–1.6× 0.2–0.4 cm, base cuneate, apex acute, margin entire; stamens numerous, filaments free, anthers yellow, obovate, 1–1.2 mm long, apex rounded, shorter than filament, with longitudinal slits. Pistillate flower: pedicel 8–1.6 cm long, hirsute; tepals 5, white to pinkish, glabrous; outer tepals 3, ovate, 0.8–1.0× 0.3–0.5 cm, apex obtuse to rounded, margin entire; inner tepals 2, ovate, 0.6–1.0× 0.2–0.4 cm, apex obtuse to rounded, margin entire; styles 3, free, stigmas bilobed, with twisted band; ovary green or pinkish, 1.5–2.0 cm long, 0.3–0.5 cm in diam., cylindric, wingless, puberulent; placentation axile, 3-locular, placentae partly branching 2–4 each locule. Fruit berrylike, wingless.

Flowering in October–December, fruiting in November–January next year.

The epithet refers to the upward fruit when nearly mature (Fig. 4-J). The erect case of fruit when nearly mature is unusual in the genus Begonia. The exceptional species is in some species in Begonia sect. Trachelocarpus (C. Müller) A. DC., such as Begonia lanceolata Vellozo in Brazil (Doorenbos et al. 1998; Tebbitt 2005).

The species just grows on soil within the secondary tropical evergreen lowland rainforest and broad-leaved forests on the slopes and ridge of crystalline limestone with highly eroded earth at an elevation 400–700 m above sea level.

The species occurs exclusively in Tuyen Quang Province in Vietnam.

VIETNAM. Tuyen Quang province, Lam Binh district, Thuong Lam community, 22°30'17"N, 105°18'48"E, 420 m a.s.l., 13 October 2017, in flower, H.Q. Nguyen et al. CPC 8449 (KUN!; CPC!). The same locality, 22°30'06"N, 105°19'29"E, 255 m a.s.l., 29 November 2017, flower pinkish, Y.M. Shui, W.H. Chen, S.W. Guo, H.Q. Nguyen,H.T. Nguyen, K. S. Nguyen, N.Q. Chuong CK1505 (KUN!; CPC!). The same place, 420 m a.s.l., 30 November 2017, in fruit, Y.M. Shui, W.H. Chen, S.W. Guo, Q.H. Nguyen, T.H. Nguyen, S.K. Nguyen CK1513 (KUN!; CPC!).

The new species should be a member of Begonia sect. Leprosae Y.M. Shui according to its clavate berry fruit (Shui et al. 2002). In the section, it is more similar to B. longicarpa and B. leprosa Hance than the other species. It is similar to B. longicarpa in the habitat of ground soil and different mainly in the petal number (5 vs. 3), the hairs of petiole (hispid vs. pubescent) and the morphology of the segments of placentation per locule (irregular placenta segments vs. 2 regular placenta segments per locule). It is also similar to B. leprosa in the morphology of the fruit and hairs on the petiole, but differs mainly in the habitat (ground soil vs. limestone surface), the abaxial surface of leaves (obviously reticulate nerves vs. obscurely reticulate nerves) and the petal number of the female (5 vs. 4) and the morphology of placentation at the upper part of ovary (axile vs. parieta). As to the white spots on the adaxial leaf surface, it is somewhat similar to Begonia gulinqingensis S.H.Huang & Y.M.Shui in Begonia sect. Diploclinium, but different in the fruit (berry vs. capsule) (Fig. 4-J; Shui and Chen 2017).