The new species is mostly similar to the green-leaved individuals of B. fimbristipula Hance (Hance 1883), but differs mainly by its leaves sparsely hairy (vs. densely hairy), with a bracteole at the top of the pistillate flower pedicel (vs. without), larger (10–12 × 12–13 vs. 6–8 × 9–11 mm) outer tepals of pistillate flower, placentae unilamellate (vs. bilamellate), and later flowering (June–July vs. April–May).

Figure 1. 

Begonia angustibracteata D.K.Tian & R.C.Hu. A habitat and habit B large stipule (left corner) and small (lower right) individuals C, D portion of leaf, adaxial (C) and abaxial (D) surface E inflorescence showing flowers F peduncle showing basal bracts G bracts, abaxial views H–J front (H), back (I) and side (J) views of staminate flower K front view of pistillate flower L side view of ovary showing a bracteole at arrow M cross-section of ovary showing placentae N side view of fruit O side view of dried fruits showing dorsal wing P adaxial view of dried fruit. (Photos by Daike Tian)

China. • Guangxi: Guiping (桂平) City, Xishan (西山) Town, Bitan (碧滩) Village (Fig. 2), near streams or on wet or slightly dry rock walls, 23°25'45"N, 109°53'9"E, elev. 38 m, dried fruits of the previous year, April 21, 2024, Daike Tian, Jinye Zhou, Renchuan Hu TDK5598 (holotype: CSH0214187; isotypes: CSH0214184, 0214185, 0214186, CSH!).

Figure 2. 

Distribution of Begonia angustibracteata (black triangle) and B. baishishanensis (black dot) in Guangxi, China.

Herb perennial, 2–20 cm tall, monoecious, tuber spherical, 8–25 mm in diameter. Leaves usually 1 per plant, sometimes 2 (more common in large plants); membranous, slightly asymmetric to near symmetrical, cordate, oval or ovate, 5–38 × 4–32 cm, wide side 2.2–17.5 cm, narrow side 2–15 cm, adaxially green, covered with very short rough hairs, hairs ≤ 0.5 mm, venation palmate, veins 10–11 (–12), concave; abaxially grayish-green, veins convex, covered with grayish-white villous, hairs 1–5 mm long, longer at the base of primary veins; margin heavily serrate and short grayish-green hairy, hairs ca. 1 mm long, apex acute and often coarsely toothed. Petioles green, light green or pink, 1.5–20 cm long, 1.5–9 mm thick, light green longitudinal spotted and grayish-white villous, hairs ≤ 6 mm long, or sparsely pale-white hairs on the upper of petioles; petiole base grooved. Inflorescence: dichasial cyme, 1 per plant, occasionally 2, 5–33 cm long; peduncle 3–23 cm long, 2–6 mm thick, reddish-brown, glabrous, 3–10 flowers per inflorescence. Bracts nearly persistent, nearly linear, 3–6 × 1–2 mm, basal bracts with 3 red longitudinal stripes, upper bracts with red midribs. Staminate flower: pedicel light green, usually gradually turning pink downwards, glabrous, 10–50 mm long, 1 mm thick; flower 16–23 × 18–25 mm; tepals 4, glabrous, outer 2 ovate, 8–12 × 8–12 mm, adaxially pink, slightly light green on the top edge, depressed and slightly thick in central part; abaxially color slightly lighter, nearly pinkish-white; inner 2 narrowly oblanceolate, pinkish-white, 9–12 × 4–5 mm, lighter and thinner than outer tepals; androecium nearly capitate, actinomorphic, 1.5–2 mm long, 2–3 mm wide; stamens 27–45, filaments basally fused, stamen column nearly 2 mm long, filaments and anthers nearly 1 mm long, fragrance pleasant. Pistillate flower: pedicel light green, glabrous, 20–24 mm long, ca. 1 mm thick, with a bracteole on the top of pedicel or below ovary, 4–5 × ca. 1.5 mm; flower 13–21 × 12–14 mm, tepals 3, glabrous, outer 2 ovate, pinkish-white, slightly flat, the middle and lower parts gradually turning dark pink, 10–12 × 12–13 mm; inner 1 oblanceolate; pistils 4–5 × 3–4 mm, styles 3, nearly free, ca. 2 mm long; ovary 3 locular, placentation axile, placentae unilamellate. Fruit: stalk 10–28 mm long, ca. 1 mm thick; capsule 6–9 × 4–6 mm, unequally 3-winged, large one nearly triangular or rectangular-triangular, 10–18 × 9–19 mm, lateral wings sickle-shaped, 1.5–3 × 8–10 mm.

Flowering June–July, fruiting July–August.

The epithet “angustibracteata” refers to the narrow bracts of this new species. The Chinese name is given as “狭苞秋海棠”.

The new species has been found only in three places restricted to Guiping City and Hengzhou City of Guangxi (Fig. 2). It grows on rock cliffs or in shaded places of valleys at an altitude of 30–300 m.

The new species has been found only in three places of Guiping and Hengzhou City (Fig. 2), the extent of occurrence is about 210 km² and the area of occupancy is about 12 km². Although one of three locations has a large number of individuals (>10000 mature individuals, and many seedlings) and new populations will be possibly discovered in other places in the future. The conservation status of this species is assessed as Endangered (EN) (B1ab(i-v)+2ab(i-v)) due to possibly partial loss of habitats caused by road construction or maintenance, following Guidelines for Using the IUCN Red List Categories and Criteria (IUCN 2024).

China. • Guangxi: Guiping City, Xishan Town, Bitan Village, near streams on wet or slightly dry rock walls, or in crevices, 23°25'45"N, 109°53'9"E, elev. 38 m, flowering, July 26, 2023, Renchuan Hu, Xincheng Qu 450881230726019 (GXMI!); • ibid., 23°25'58"N, 109°53'23"E, elev. 57 m, few dried fruits of the previous year, April 21, 2024, Daike Tian, Jinye Zhou, Renchuan Hu TDK5599 (CSH!). • Guiping City, Jiangkou (江口) Town, Litang (理塘) Village, growing on rock wall or in crevices between rocks of Danxia landform, 23°40'57"N, 110°13'44"E, elev. 299 m, April 21, 2024, few dried fruits of the previous year, Daike Tian, Jinye Zhou, Renchuan Hu TDK5601 (CSH!); • Hengzhou (横州) City, Zhenlong (镇龙) Town, growing on wet rock wall or in rock crevices, along a river valley in Jiulong Waterfall Group National Forest Park (九龙瀑布群国家森林公园), 23°3'23'N, 109°13'39"E, elev. 264 m, few dried fruits of the previous year, April 25, 2024, Daike Tian, Jinye Zhou, TDK5639 (CSH!); • ibid., 23°3'0"N, 109°13'39"E, elev. 237 m, without flower, April 25, 2024, Daike Tian, Jinye Zhou, TDK5642 (CSH!).

Begonia baishishanensis is most similar to B. danxiaensis D.K.Tian & X.L.Yu (Tian et al. 2019), but differs in its larger (3–21 × 2.6–20.3 cm vs. 2–13 × 1.5–13.5 cm) and thicker (vs. thinner) leaves, hairy (vs. nearly glabrous) bract margins, larger outer tepals of staminate flower (13–17 × 10–14 mm vs. 4–11 × 3–10 mm) and pistillate flower (10–13 × 11–15 mm vs. 3–9 × 4–9 mm), more (47–88 vs. 10–38) stamens, and placentae bilamellate (vs. unilamellate). The species is also similar to B. fimbristipula (Hance, 1883) belonging to B. section Diploclininum, but mainly differs by its larger (3–21 × 2.6–20.3 cm vs. 4–13 × 4.8–8.5 cm) and thicker (vs. thinner) leaves, shorter (≤ 0.5 mm vs. ≥ 1 mm long) hairs on adaxial leaf surface, larger outer tepals of pistillate flower (13–17 × 10–14 mm vs. 8–13 × 8–10 mm) and pistillate flower (10–13 × 11–15 mm vs. 6–8 × 9–11 mm).

Figture 3. 

Begonia baishishanensis R.C.Hu & D.K.Tian A habitata in Baishishan landform in Guiping of Guangxi B, C habit and plants in late flowering D individual plants showing size variation E abaxial blade surface of red leaf individual F abaxial leaf surface and petiole showing indumentum G adaxial leaf surface H bract I front view of staminate flower J front view of pistillate flower K cross-section of ovary showing bilamellate placentae L young fruits showing shape variation of large wings. (Photos by Daike Tian).

China. • Guangxi; Guiping City, Madong (麻垌) Town, Baishi (白石) Village (Fig. 2), growing on rock walls or with grasses of Danxia landform mountain, 23°42'8"N, 110°12'19"E, elev. 383 m, late flowering, April 21, 2024, Daike Tian, Jinye Zhou, Renchuan Hu TDK5596 (holotype: CSH0214176; isotypes: CSH0214177, 0214178, 0214179, CSH!).

Herb perennial, 3–15 cm tall, monoecious, tuber spherical, usually 2–3 connected, 8–30 mm in diameter; erect stem absent or with 1 at anthesis, 0.2–4 cm long, 3–8 mm thick. Stipules long triangular, ca. 6 mm long, covered with grayish-white long rough hairs. Leaves usually 1, rarely 2 per plant, blade cordate, nearly symmetrical, 3–21 × 2.6–20.3 cm, wide side 1.4–10.1 cm, narrow side 1.2–10.1 cm; adaxially green, rarely dark green, covered with grayish-white short rough hairs, hairs usually ≤ 1 mm long, venation palmate, veins 9–10, concave; abaxially gray-green, rarely purple-red, grayish-white villous, hairs 1–5 mm long, longer (up to 4 mm) at the base of primary veins, primary veins convex, secondary veins slightly convex; lobes of leaf base valvate to acute angled or slightly overlapped, margin with few serrate and short cilia, apex acuminate or short acuminate. Petioles green, rarely red, 0.8–18 cm long, 1.2–6 mm thick, grayish-white villous, hairs up to 4 mm long, denser on the top position. Inflorescence: dichasial cyme, basal, usually 1, rarely 2 per plant, 4–40 cm long, peduncle 1.5–24 cm long, 0.8–8 mm thick, nearly glabrous, 2–15 flowers per inflorescence. Bracts light green, long triangular to nearly lanceolate, 4–11 × 1.5–5 mm, margin ciliate. Staminate flower: pedicel greenish-white with pink, glabrous, 10–19 mm long, 0.6–0.8 mm thick; flower 26–34 × 25–31 mm, tepals 4, pink, coloration even, glabrous; outer 2 ovate or oval, 13–17 × 10–14 mm; inner 2 nearly obovate or obovate-lanceolate, 11–19 × 7–9 mm; androecium nearly capitate, actinomorphic, 3–4 × 4–5 mm; stamens 47–88; filaments base fused, connate part ca. 1.5 mm long, free part 1–1.5 mm long, anthers 0.8–1 mm long. Pistillate flower: pedicel pink, glabrous, 8–13 mm long, 0.6–0.8 mm thick; flower 22–26 × 12–19 mm, tepals 3, pink, coloration nearly even, glabrous; outer 2 broadly ovate or ovate, slightly flat, 10–13 × 11–15 mm; inner 1 obovate or obovate-lanceolate, 6–12 × 3–7 mm; pistils 4–5 × 3–5 mm; styles 3, nearly free, 1.5–2 mm long; ovary 3 locular, placentation axile, placentae bilamellate. Fruit: stalk 11–20 mm long, ca. 1 mm thick, capsule 8–11 × 6–9 mm, unequally 3-winged, larger one nearly rectangular or triangular-rectangular, 11–15 × 10–15 mm, apex nearly obtuse or pointed; smaller wings sickle-shaped, 1–2 × 7–16 mm.

Flowering March to April, fruiting April to May.

The epithet “baishishanensis” refers to Baishishan, a mountain name of Guiping City and the type locality of this species. The Chinese name is given as “白石山秋海棠”.

One population including four subpopulations of B. baishishanensis are found on rock walls or grass, or in rock crevices of Danxia landform cliff of Baishishan of Guiping City, Guangxi, China (Fig. 2).

The new species is only found in the type locality, the extent of occurrence is about 2 km² and the area of occupancy is less than 2 km², and has only one population (< 2000 mature individuals, and few seedlings). Due to its unique habitat and negative influence by tourism, its living space is shrinking, currently it is assessed as Critically Endangered (CR) (B1ab(i–v)+2ab(i–v)) following Guidelines for Using the IUCN Red List Categories and Criteria (IUCN 2024). Therefore, B. baishishanensis should be suggested to be included in the future List of China National Protected Wild Plants. However, further investigation is necessary on its actual distribution area and the number of populations and individuals.

China. • Guangxi: Guiping City, Madong Town, Baishi Village, growing on rock wall or grass of Danxia landform mountain, 23°42'8"N, 110°12'19"E, elev. 383 m, peak flowering, March 25, 2024, Renchuan Hu Xincheng Qu, TDK5596 (CSH!).