Begonia prolifera A. DC., a newly recorded species of Begoniaceae from China

Begonia Linnaeus (Begoniaceae) is the sixth largest genus of angiosperms^[1], and currently contains of 2117 accepted species^[2] distributed in the tropics and subtropics of Asia, America, and Africa. In total, 267 species have been recorded according to Flora of China^[3] and recent publications^[4-7], including 118 in Yunnan^[8]. During botanical surveys of the China-Myanmar transboundary region in Yunnan, an unknown species of Begonia was collected from the Yunnan Tongbiguan Provincial Nature Reserve. After careful examination of relevant specimens and literature on the genus within adjacent countries^[9], we identified these specimens as Begonia prolifera A. DC.^[10], which was originally described from Myanmar. Consequently, we confirmed it as a newly recorded species to China.

独叶秋海棠 (新拟, Fig. 1, Fig. 2)

Figure  1.  Begonia prolifera A. DC.

A, B: Habitat; C: Tuber; D, E: Plant (front and back view); F: Infructescence (after alcohol immersion); G: Tubercle in leaf margin; H: Stem and inflorescence base; I: Staminate flower; J: Pistillate flower; K: Cross-section of ovary. (All photographs are by Hongbo Ding).

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Figure  2.  Type of Begonia prolifera A. DC. and specimens from Thailand and China

A: Type specimen from Myanmar; B: Specimen from Thailand; C: Specimen from China.

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Begonia prolifera A. DC., Ann. Sci. Nat., Bot. sér. 4, 11: 135. 1859; Phutthai, T., et al. in Santisuk, T. (ed.), Fl. Thailand 14(3): 408. 2019.

Type: Myanmar, Moulmein, 1846, Lobb, T., 381 (Isotypes: K000761448, K000761449, K000761450, BM000020324, E00265067, E00265068).

Herb tuberous, monoecious, 10−25 cm tall; tuber solitary, globose with numerous fibrous roots, creamy-white, 5−8 mm diameter. Stem upright, light green, 3−12 cm long, glabrous, succulent, adaxially grooved; Stipule not seen. Leaf unifoliate, sessile, lamina basifixed, symmetric or subsymmetric, orbicular-cordate, 8−16 × 9−18 cm, base cordate, apex acute, margin dentate to slightly incised, sometimes with densely small tubercle at margin, adaxially deep green, subglabrous or sometimes with sparse white hispid, abaxially light green, subglabrous; venation palmate, veins 8−10, prominent abaxially. Inflorescence 10−18 cm long, arising from top of stem with leaves, thyrsoid cyme, peduncle light green or reddish brown, subglabrous. Staminate flower: pedicel pinkish-white, subglabrous, 5−10 mm long; tepals 4, outer 2, white or pinkish-white, orbicular, 4−5 × 4−5 mm, apex rounded, margin entire, glabrous on both sides; inner 2, white or pinkish-white, glabrous, ovate, 3−3.5 × 1.5−2 mm, apex obtuse, margin entire, glabrous on both sides; androecium actinomorphic, globose, stamens 10–13, yellow, filaments fused at base, 0.5–0.8 mm long; anthers obovate, yellow, ca. 1 mm. Pistillate flower: pedicel white or pinkish-white, subglabrous, 3−6 mm long; tepals 5, white or pinkish-white, unequal, 4, orbicular to obovate, 6−7 × 4.5−6 mm, apex rounded, margin entire, glabrous on both sides; 1, smaller, obovate, white or pinkish-white, 5−6 × 2−3 mm, apex rounded, margin entire, glabrous on both sides; styles 2, ca. 3 mm long, fused at base, yellow, stigmatic band crescent-shaped; ovary white, subglabrous, unequally 3-winged, 2-locular, placentation axile, placentae bifid. Capsule nodding, pale green, drying pale brown, 13−25 × 10−14 mm, subglabrous, unequally 3-winged, abaxial wing oblate-triangular, 10−18 × 8−12 mm, apex acute, lateral wings smaller, 3−6 × 8−12 mm.

Phenology: Flowering from July to August; Fruiting from August to November.

Distribution: Begonia prolifera is now known from Yunnan Province, China, Thailand, and Myanmar (type).

Specimens examined: China: Yunnan, Dehong, Yingjiang, Nabang Town, Tongbiguan Provincial Nature Reserve, near Kangguangka River, 24°41' N, 97°35' E, elev. ca. 489 m, 27 August 2021, Mamai Yue T0957 (HITBC); Nabang Town, Tongbiguan Provincial Nature Reserve, near Wajiao River, 24°43' N, 97°35' E, elev. ca. 495 m, 3 August 2022, Hongbo Ding et al. WPY297 (HITBC); Myanmar: Moulmein (Mawlamyaing), 1846, Lobb, T., 381 (K000761448, K000761449, K000761450, BM000020324, E00265067, E00265068); Thailand: Kanchanaburi Province, Sangklaburi District, Toong Yai Naresuan Wildlife Reserve, Lai Wo Subdistrict, Ban Saneh Pawng (Karen Village), elev. ca. 250 m, 8 October 1993, J. F. Maxwell 93-1167 (L3737366); Mae Hong Son Province, Mae Sariang District, Tambon Mac Ho, Lod cave, elev. ca. 700 m, 22 December 2010, Suksathan, P., 5332 (L4311346); Kanchanaburi Province, Sangklaburi District, Khao Laem National Park, on limestone rock, 98°37'53" E, 14°58'53" N, elev. ca. 265 m, 14 October 2013, Ching-I Peng 24175 (HAST136075).

Notes: Begonia prolifera shares similarities to B. subperfoliata Parish ex Kurz from Myanmar and China but differs significantly by lamina cordate (versus peltate), styles 2 (versus 3), and ovary 2-locular (versus 3-locular). This species belongs to Begonia sect. Monophyllon A. DC., which previously comprised only four species (B. prolifera A. DC., B. paleacea Kurz, B. lanxangensis Souvann. & Aver., and B. oyuniae M. Taram & N. Krishna). Morphologically, members of this section are well defined and characterized by upright stems and inflorescences emerging from the top or slightly below the stem^[11]. Among the four species in sect. Monophyllon, B. oyuniae M. Taram & N. Krishna was first described and published by Taram et al. in 2020^[11], with images closely resembling those of B. prolifera from China and Myanmar, except for the position of the inflorescence, which arises from the base of the leaf blade or slightly below on the petiole (versus on top of the stem). This raises the question of whether it is a synonym of B. prolifera, thus necessitating further studies for clarification. The Chinese records of B. prolifera well align with the protologue and type specimen. The known distribution of B. prolifera includes two small populations in Tongbiguan Provincial Nature Reserve, Yingjiang County, China, but it is likely to have wider distribution on limestone outcrops in the transboundary region between China and Myanmar. Given the challenge in accessing its friable limestone habitat during the wet season and its transformation into a small tuber during the dry season, observations of this species in the field are difficult^[9].

Acknowledgments: We are grateful to Zhenghua Yang, Yongsheng Zhang, San Xiong, Chuncheng Duan, Zuwei Yang, and Kaifan Li from the Tongbiguan Provincial Nature Reserve for help during field work. We are also grateful to Wendun Deng, Chewei Lin, Bingmou Wang, and Chih-Chieh Yu for help with taxonomy. We are also grateful to the keepers of the K, BM, E, L, and HAST herbaria for kind assistance during specimen examinations.