Begonia guangdongensis is morphologically similar to B. biflora T. C. Ku (Wu and Ku 1997), B. longistyla Y. M. Shui & W. H. Chen (Shui and Chen 2005) and B. chongzuoensis Yan Liu, S. M. Ku & C.-I Peng (Peng et al. 2012) by sharing obliquely ovate asymmetric leaves, hairy petioles, a glabrous peduncle, 2–3 times branched dichasial cyme and glabrous trigonous-ellipsoid capsules. However, it can be easily distinguished from B. biflora by its stipules with aristate apex and without ciliate margin (vs. aristate and ciliate apex and ciliate margin), rugose leaves (vs. flat) and glabrous capsules (vs. pubescent); it differs from B. longistyla by its abaxially glabrous stipules without ciliate margin (vs. abaxially hairy stipules with ciliate margin), leaves densely hirsute-pilose (vs. densely tuberculate-based pilose-setula) and inflorescence equal or slightly shorter than petioles (vs. much longer) and it can be distinguished from B. chongzuoensis by its persistent stipules and bracts (vs. caducous), rugose leaves (vs. nearly flat), leaves densely white hirsute-pilose (vs. moderately to sparsely whitish-hyaline or reddish setulose) and an unequally 3-winged capsule (vs. equal or subequal). (Table 1).

Figure 1. 

Begonia guangdongensis A plant B₁ close up of adaxial surface of leaf B₂ close up of abaxial surface of leaf C stipule D bract E₁ and E₂ staminate flower F androecium G₁ and G₂ pistillate flower H style and stigma I cross section of ovary in the middle part J immature capsule. Drawn by Zheng-meng Yang.

China. Guangdong Province, Yangchun City, Chunwan Town, on a slope of a limestone hill in an evergreen forest, 22°21'44.04"N, 111°57'26.28"E, alt. 88 m, 6 October 2019, Li et al. 263 (holotype, CANT!; isotype, IBSC!).

Perennial herbs, rhizomatous. Rhizomes creeping, red, stout, 7–12 mm in diam., internodes 4–7 mm long, sparsely hairy. Leaves simple and alternate; stipules generally persistent, ovate-triangular, 5–8 × 3–5 mm, apex aristate, arista ca. 1.5 mm long, abaxially glabrous; petioles red, ca. 15–30 cm long, with densely white villose, ± reflexed trichomes; blades basifixed, asymmetric, obliquely ovate, 10–18 × 7–13 cm, papery, rugose, adaxially densely white hirsute-pilose, veins depressed, abaxially hirsute-pilose, denser on primary veins, veins convex, base obliquely deeply cordate, apex acuminate or caudate, margin irregularly repand serrate and ciliate; basal palmate veins 6–7. Inflorescences axillary, arising directly from rhizome, flowers 6–15 in a 2–3 times branched dichasial cyme; peduncles 15–20 cm long, equal or slightly shorter than petioles, glabrous; bracts oblong, 2–3 × 1–1.5 mm, apex obtuse, margin serrulate and ciliate. Staminate flowers: pedicel 1–1.5 cm long, glabrous; tepals 4, outer 2 ovate to suborbicular, 9–14 × 8–13 mm, upper side pinkish-white, lower side pink with red nerves, glabrous on both sides, inner 2 white, oblong or narrowly elliptic, 7–9 × 3–4 mm, glabrous; androecium actinomorphic, nearly spherical, yellow, stamens numerous, filaments nearly free, 1–1.5 mm long, anthers obovate, ca. 1.2 × 0.7 mm, apex emarginated. Pistillate flower: pedicle 1–1.5 cm; tepals 3, outer 2 broadly ovate to suborbicular, 6–9 × 8–12 mm, pink with red nerves, glabrous on both sides, inner 1 of left side white, oblong or ovate-lanceolate, 5–6 × 2–3 mm; styles 3, fused at base, yellow, ca. 1.5–2 mm long, the upper 2-cleft; stigmas spirally twisted; ovary trigonous-ellipsoid, dark pink, 1-locular with parietal placentation, glabrous, 3-winged. Capsule nodding, trigonous-ellipsoid, apex obtuse, 8–10 mm long, 5–7 mm in diam. (wings excluded), surface with a few small red spots, unequally 3-winged, abaxial wing lunate, 2.5–5 mm wide, lateral wings 2–3 mm wide, glabrous.

Figure 2. 

Habitat and morphology of Begonia guangdongensis A, B habitat C habit D petiole E close up of petiole F view of abaxial surface of leaf G view of adaxial surface of leaf H close up of adaxial surface of leaf I rhizome J inflorescences K view of adaxial surfaces of staminate and pistillate flower L view of abaxial surfaces of staminate and pistillate flower M androecium N styles and stigmas O immature capsule P cross section of ovary in the middle part Q dry bract R dry stipule.

Flowering in September to October, fruiting in October to November.

The new species is named after the type locality, Guangdong Province, China.

This new species grows on the slope of a limestone hill in evergreen forests at an elevation of 80–100 m (Fig. 3).

Only one population of this new species was discovered in Guangdong Province in China.

Figure 3. 

Distribution map of B. biflora, B. longistyla, B. chongzuoensis and B. guangdongensis.

Critically Endangered (CR). Limestone areas in Chunwan Town have been searched for this new species, but Begonia guangdongensis is known only from one population consisting of ca. 100 mature individuals. The area of occupancy (AOO) of the species is estimated to be less than 4 km², which indicates the species belongs in the Critically Endangered category under criterion B2, according to the IUCN Red List Categories and Criteria (IUCN 2019). Since the species grows on a limestone hill near two cement factories, the species is threatened by the limestone quarrying. Its habitat will likely be destroyed since the area is undergoing a continuing decline. Based on the current information (one location with area in continuing decline and AOO less than 10 km²), the new species can be assessed as Critically Endangered [B2ab(iii)] (IUCN 2019).

Begonia guangdongensis, belonging to Begonia sect. Coelocentrum, is a very distinctive species in having leaf features, such as rugose and densely hirsute-pilose leaves and an obtuse apex of the capsules. Although it is more or less similar to B. biflora, B. longistyla and B. chongzuoensis in their obliquely ovate asymmetric leaves and glabrous trigonous-ellipsoid capsules, it differs from B. biflora by its sparsely hairy and smooth rhizomes (vs. rough rhizomes with many membranous scales), leaves with densely hirsute-pilose and depressed veins on adaxial surface (vs. with sparsely setula and veins not depressed) and stipule and capsule features discussed in the above diagnostic description. However, B. guangdongensis is quite different from B. longistyla, being distinguished by its oblong bracts with obtuse apex (vs. ovate bracts with a tip apex), stipule and leaf pubescence, length of inflorescence and capsules features. B. guangdongensis is also markedly distinct from B. chongzuoensis by its stipules, leaf and bract and capsule features. In addition, their distribution range is different (Fig. 3). Both B. biflora and B. longistyla are distributed in Yunnan Province and B. chongzuoensis in Guangxi Province, whereas B. guangdongensis occurs in Guangdong Province. Additionally, B. guangdongensis flowers in September to October, while B. biflora flowers in May, B. longistyla in April to June and B. chongzuoensis in May to September. Thus, even if they were growing together, they would be genetically isolated in time.