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Research Article
A new species (Begonia giganticaulis) of Begoniaceae from southern Xizang (Tibet) of China
expand article infoDai-Ke Tian‡§, Wen-Guang Wang|, Li-Na Dong, Yan Xiao‡§, Min-Min Zheng‡§#, Bin-Jie Ge‡§
‡ Shanghai Chenshan Plant Science Research Center, Chinese Academy of Sciences, Shanghai, China
§ Shanghai Chenshan Botanical Garden, Shanghai, China
| Xishuangbanna Tropical Botanical Garden, Mengla, China
¶ Guangxi Institute of Botany, Guangxi Zhuang Autonomous Region and Chinese Academy of Sciences, Guilin, China
# University of Chinese Academy of Sciences, Beijing, China

Corresponding author: Dai-Ke Tian ( dktian@cemps.ac.cn )

Academic editor: Jan Wieringa
© 2021 Dai-Ke Tian, Wen-Guang Wang, Li-Na Dong, Yan Xiao, Min-Min Zheng, Bin-Jie Ge.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Tian D-K, Wang W-G, Dong L-N, Xiao Y, Zheng M-M, Ge B-J (2021) A new species (Begonia giganticaulis) of Begoniaceae from southern Xizang (Tibet) of China. PhytoKeys 187: 189-205. https://doi.org/10.3897/phytokeys.187.75854
Open Access

Abstract

Begonia giganticaulis, a huge new species in Begonia sect. Platycentrum of Begoniaceae from southern Xizang (Tibet) of China, is described. Morphologically, it is mostly similar to B. longifolia and B. acetosella, but clearly differs from the former mainly by its dioecious and taller plants, sparse hairs on abaxial veins, longer inflorescence, unique shape of fruits, and differs from the latter mainly by its late and longer flowering time, 6-tepals of female flower and 3-loculed ovary. The phylogenetic analyses also support the separation of the new species from other taxa. Based on the current data, its conservation status is assigned to Endangered (B2a) according to the IUCN Red List Categories and Criteria.

Keywords

Conservation status, molecular evidence, morphology, southern Tibet, taxonomy

Introduction

Zangnan (southern Tibet) of China is located to the south of the Himalayas, including most parts of Cona, Lhünzê, Mêdog and Zayü counties, and some smaller parts of Nang and Mainling counties (Liu 2019). This region is very warm and rainy because of the southwest monsoon carrying heavy water and heat from the Indian Ocean. Owing to high average annual precipitation and high-proportion of forest coverage (Hao et al. 2010), the plant diversity is very high in Zangnan. However, this area still remains under-explored and needs more study in the future.

After a series of plant surveys recently, the authors have a better understanding of the diversity of Begonia in Tibet, particularly in its southern part (namely Zangnan) including Mêdog county. Up until now, 39 species and 4 varieties had been found in Tibet (Gu et al. 2007; Camfield and Hughes 2018; Tian et al. 2020) (Table 1). In addition, Begonia limprichtii Irmsch. (Irmscher 1922) was newly reported by Borah et al. (2021a) in southern Tibet, but this record is likely based on a wrong identification and further study is needed. Of these, 31 species and 3 varieties are distributed in Mêdog. Recently, after several field surveys in Mêdog, we found several new species and at least three natural hybrids. Here we described Begonia giganticaulis D.K.Tian & W.G.Wang sp. nov. from Mêdog, a new species of huge plant size, which is morphologically similar to both B. longifolia Blume (Blume 1827) and B. acetosella Craib (Craib 1912). The morphological differences of the three species are compared, and the new species is also supported by molecular evidence.

Table 1.
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A checklist of Begonia species in Tibet.

Species Reference County
Begonia aborensis Dunn Dunn 1920 Mêdog
Begonia acetosella Craib Craib 1912 Mêdog
Begonia annulata K.Koch Koch 1857 Mêdog
Begonia asperifolia Irmsch. Irmscher 1927 Bomê, Zayü, Lhünzê, Mêdog
Begonia burkillii Dunn Dunn 1920 Mêdog
Begonia cathcartii Hook.f. & Thomson Hooker 1855 Zayü
Begonia dioica Buch.-Ham. ex D.Don Don 1825 Dinggyê
Begonia difformis (Irmsch.) W.C.Leong, C.I Peng & K.F.Chung Leong et al. 2015 Mêdog
Begonia flagellaris Hara Hara 1973 Gyirong, Nyalam
Begonia flaviflora var. flaviflora Hara Hara 1970 Mêdog
Begonia flaviflora var. gamblei (Irmscher) Golding & Karegeannes Golding and Karegeannes 1984 Mêdog
Begonia giganticaulis D.K.Tian & W.G. Wang sp. nov. In this study Mêdog
Begonia grandis Dryand. Dryander 1791 Zayü
Begonia griffithiana (A.DC.) Warb. Warburg 1894 Mêdog
Begonia handelii Irmsch. Irmscher 1921 Mêdog
Begonia hatacoa Buch.-Ham. ex D.Don Don 1825 Mêdog, Cona
Begonia iridescens Dunn Dunn 1920 Mêdog, Zayü
Begonia josephii A.DC. de Candolle 1859 Cona, Dinggyê, Lhünzê, Mêdog, Yadong
Begonia kekarmonyingensis Taram, D.Borah & M.Hughes Taram et al. 2021 Mêdog
Begonia labordei H.Lév. Léveillé 1904 Zayü
Begonia limprichtii Irmsch.*(wrong identification, based on the distribution and morphological characteristics) Borah et al. 2021a Mêdog
Begonia longifolia Blume Blume 1827 Mêdog
Begonia medogensis J.W.Li, Y.H.Tan & X.H.Jin Li et al. 2018 Mêdog
Begonia megaptera A.DC. de Candolle 1859 Zayü
Begonia nepalensis (A.DC.) Warb. Warburg 1894 Cona
Begonia ovatifolia A.DC. de Candolle 1859 Mêdog
Begonia oyuniae M.Taram & N.Krishna Taram et al. 2020 Mêdog
Begonia plamata var. plamata D.Don Don 1825 Mêdog
Begonia palmata var. bowringiana (Champion ex Bentham) Golding & Karegeannes Golding and Karegeannes 1984 Mêdog
Begonia palmata var. khasiana (Irmsch.) Golding & Kareg Golding and Karegeannes 1984 Mêdog
Begonia pasighatensis D.Borah, Taram & Wahlsteen Borah et al. 2021b Mêdog
Begonia picta Sm. Smith 1805 Gyirong, Mêdog, Nyalam
Begonia pseudoheydei Y.M.Shui & W.H.Chen Chen et al. 2019 Mêdog
Begonia rex Putz. Putzey 1857 Mêdog
Begonia roxburghii (Miq.) A.DC. de Candolle 1864 Mêdog
Begonia scintillans Dunn Dunn 1920 Mêdog
Begonia shilendrae Rekha Morris & P.D.McMillan Morris and McMillan 2012 Cona
Begonia sikkimensis var. sikkimensisA.DC. de Candolle 1859 Mêdog
Begonia sikkimensis var. kamengensis Rekha Morris, P.D.McMillan & Golding ex Golding Golding 2009 Cona
Begonia silletensis Clarke Clarke 1879 Mêdog
Begonia tessaricarpa C.B.Clarke Clarke 1879 Mêdog
Begonia thomsonii A.DC. de Candolle 1859 Mêdog
Begonia xanthina Hook.f. Hooker 1852 Mêdog
Begonia zhongyangiana W.G.Wang et S.Z.Zhang Wang et al. 2019 Mêdog

Material and methods

Morphological analysis

The field surveys were conducted on habitat, distribution, population size, morphology and specimen collection of the new species. Diagnosis of the morphological difference between the new species and its similar species was based on literature review, examination of herbarium specimens, and observation of both wild and cultivated plants.

Phylogenetic analysis

The treatment on sections of Begonia follows Shui et al. (2019). To ascertain the relationship of the new species within sect. Platycentrum (Klotzsch) A.DC. (de Candolle 1859), two female and three male individuals were sampled, and three individuals of B. longifolia, two individuals of B. acetosella, and three individuals of B. acetosella var. hirtifolia Irmsch. (Irmscher 1939) were sampled and sequenced. 13 taxa within sect. Platycentrum were selected based on Moonlight et al. (2018) to ascertain the phylogenetic relationship of the new species. Begonia cavaleriei H.Lév. (Léveille 1909) from sect. Coelocentrum Irmsch. (Irmscher 1939) was used as outgroup. All the voucher specimens were deposited in the herbarium of Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences (HITBC). For DNA sequencing, the total genomic DNA was extracted from silica-dried leaves by a modified CTAB protocol (Doyle and Doyle 1987). The chloroplast DNA rpL16 intron, ndhA intron and the nuclear ribosomal DNA internal transcribed spacer (nrITS) region were used to infer the phylogenetic relationship of the new species. The rpL16 intron were amplified by the primer rpL16-F and rpL16-R and sequenced by the primer rpL16-R and Beg-rpL16 (Chung et al. 2014). For the amplification of the ndhA intron the primer ndhAX1 and ndhAX2 (Thomas et al. 2011) were used. The nrITS region was amplified and sequenced by the primer 51NT and 26S1Rev (Clement et al. 2004). The sampled sequences were downloaded from NCBI and accession numbers were listed in Table 2.

Table 2.
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Sampled taxa and GenBank accession numbers of Begonia giganticaulis and the related taxa used for phylogenetic analysis.

Taxa Collector, Voucher (Herbarium) Origin ITS rpL16 ndhA References
Begonia acetosella Craib Wang, W.G., WWG004 (HITBC) Mengla, Yunnan, China MW690105 MW658199 MW658212 In this study
B. acetosella Craib Wang, W.G., WWG005 (HITBC) Mengla, Yunnan, China MW690106 MW658200 MW658213 In this study
B. acetosella var. hirtifolia Irmsch. Wang, W.G., WWG0261 (HITBC) Ruili, Yunnan, China MW690107 MW658201 — In this study
B. acetosella var. hirtifolia Irmsch. Wang, W.G., WWG0262 (HITBC) Ruili, Yunnan, China MW690108 MW658202 MW658214 In this study
B. acetosella var. hirtifolia Irmsch. Wang, W.G., WWG0300 (HITBC) Ruili, Yunnan, China — MW658203 MW658215 In this study
B. aptera Blume — — AJ491196 — JF756369 Chiang (unpublised); Thomas et al. (2011)
B. balansana Gagnep. — — AF485091 KF707939 MH207051 Forrest and Hollingsworth (2003); Chung et al. (2014); Moonlight et al. (2018)
B. cathayana Hemsl. — — AF280106 KF707948 KT599095 Yang et al. (unpublished); Chung et al. (2014); Zhao (unpublished)
B. cavaleriei H.Lév. — — KF636430 KF707949 MK548079 Chung et al. (2014); Tong et al. (2019)
B. decora Stapf — — KF636435 KF707956 JF756355 Chung et al. (2014); Thomas et al. (2011)
B. giganticaulis D.K.Tian & W.G.Wang Wang, W.G., Li, Y.Y., Ma, X.D. & Shen, J.Y., WWG2014–1 (HITBC) Mêdog, Tibet, China MW690097 MW658191 MW658204 In this study
B. giganticaulis D.K.Tian & W.G.Wang Wang, W.G., Li, Y.Y., Ma, X.D. & Shen, J.Y., WWG2015–1 (HITBC) Mêdog, Tibet, China MW690098 MW658192 MW658205 In this study
B. giganticaulis D.K.Tian & W.G.Wang Wang, W.G., Li, Y.Y., Ma, X.D. & Shen, J.Y., WWG2015–2 (HITBC) Mêdog, Tibet, China MW690099 MW658193 MW658206 In this study
B. giganticaulis D.K.Tian & W.G.Wang Wang, W.G., Li, Y.Y., Ma, X.D. & Shen, J.Y., WWG2014–3 (HITBC) Mêdog, Tibet, China MW690100 MW658194 MW658207 In this study
B. giganticaulis D.K.Tian & W.G.Wang Wang, W.G., Li, Y.Y., Ma, X.D. & Shen, J.Y., WWG2014–2 (HITBC) Mêdog, Tibet, China MW690101 MW658195 MW658208 In this study
B. handelii Irmsch. — — AF485093 KF707969 MH207176 Forrest and Hollingsworth (unpublished); Chung et al. (2014); Moonlight et al. (2018)
B. hatacoa Buch.-Ham. ex D.Don — — AF485111 KF707970 JF756354 Forrest and Hollingsworth (unpublished); Chung et al. (2014); Thomas et al. (2011)
B. longifolia Blume Wang, W.G., WWG001 (HITBC) Mengla, Yunnan, China MW690102 MW658196 MW658209 In this study
B. longifolia Blume Wang, W.G., WWG002 (HITBC) Mengla, Yunnan, China MW690103 MW658197 MW658210 In this study
B. longifolia Blume Wang, W.G., WWG003 (HITBC) Mengla, Yunnan, China MW690104 MW658198 MW658211 In this study
B. nepalensis (A.DC.) Warb. — — AY753726 — MH207257 Tebbitt et al. (2006); Moonlight et al. (2018)
B. obovoidea Craib — — — — JF756386 Thomas et al. (2011)
B. pavonina Ridl. — — KF636472 KF708002 JF756356 Chung et al. (2014); Thomas et al. (2011)
B. pedatifida H.Lév. — — MK541092 MK548068 MK548115 Tong et al. (2019)
B. roxburghii A.DC. — — AF485092 — JF756371 Forrest and Hollingsworth (2003); Thomas et al. (2011)
B. versicolor Irmsch. — — AF485090 KF708023 JF756358 Forrest and Hollingsworth (unpublished); Chung et al. (2014); Thomas et al. (2011)

Sequences of each DNA region were aligned by MUSCLE online (https://www.ebi.ac.uk/Tools/msa/muscle/, Madeira et al. 2019) and adjusted manually when necessary. Indels were treated as gap. For testing the congruence within rpL16 intron, ndhA intron and nrITS, the analysis of the incongruence length difference (ILD) was performed with 100 replicates under default heuristic search using PAUP v.4.0a (Swofford 2002) and the phylogenetic trees were constructed based on each dataset. The p value was 0.40 and no conflict among each phylogenetic trees, indicating the congruence among these datasets (Farris et al. 1994).

The parsimony analysis was conducted using PAUP v.4.0 b10 (Swofford 2002). The Maximum Parsimony (MP) analysis was run using a heuristic search with 1, 000 replicates and tree-bisection-reconnection (TBR) with no reconnection limit. Bootstrap was used to assess the node support by 1000 replicates using TBR branch swapping. The Bayesian analysis was conducted using MrBayes v.3.1.2 (Ronquist and Huelsenbeck 2003) with 1, 000, 000 generations under the Markov chain Monte Carlo (MCMC) chains. The average standard deviation of split frequencies was 0.004210 after 1, 000, 000 generations. The consensus tree was constructed after burn-in 25% of the trees. The Posterior Probability (PP) was used to assess the branch supports.

Results

Taxonomic treatment

Begonia giganticaulis D.K.Tian & W.G.Wang, sp. nov.

urn:lsid:ipni.org:names:77234844-1
Figs 1, 2, 3, 4 巨型秋海棠

Type

China. Xizang (Tibet) Autonomous Region: Mêdog county (墨脱县), Beibeng town (背崩乡), Baimu Xiri river (白母西日河), forest slope of river valley or water’s edge along stream, 29°21'9"N, 95°11'21"E, elev. 1320 m, 10 September 2020, Dai-Ke Tian, Fang Wen, Qing-Gong Mao, & Zhu Lu, TDK4773-A (holotype CSH! Barcode number: 0180561, ♀)

Figure 1. 

Habitat and large-sized plant of Begonia giganticaulis D.K.Tian & W.G.Wang, sp. nov. A habitat showing plants (arrows indicate) growing along stream bank B flowering plant growing along slope of valley C one of the tallest individuals with Dr. Dai-Ke Tian. (Photos A by Dai-Ke Tian B by Shi-Wei Guo C by Qing-Gong Mao).

Figure 2. 

Morphology of Begonia giganticaulis D.K.Tian & W.G.Wang, sp. nov. A one of the single tallest plants cut into four sections B main stem base C stems showing colour of nodal cross-sections D main stem with much expanded node and whitish-green lines or spots E expanded node on terminal branch F, G male plant branches showing inflorescences and different colours H female branches I adaxially (left) nearly glabrous and abaxially sparse hairs on veins (right, arrows indicate) on blade surfaces J stipules showing shape and colour. (Photo F by Wen-Guang Wang; others by Dai-Ke Tian).

Figure 3. 

Flower and fruit morphology of B. giganticaulis compared with its close species B. longifolia and B. acetosella A–H Begonia giganticaulis A staminate flowers with pinkish outer tepals B staminate flowers with white tepals C, D pistillate flower E ovary sections showing different colour F fruits on branch G, H dorsal and front views of fruits I–K B. longifolia I flowering and fruiting branch J fruits showing short horns K ovary dissection L–O B. acetosella L staminate flower M Pistillate flower N, O fruits with short horns or wings. (Photos C by Shi-Wei Guo E (left) L, M & O by Wen-Guang Wang; others by Dai-Ke Tian).

Diagnosis

The new species is mostly similar to B. longifolia and B. acetosella, but clearly differs from the former mainly by its dioecious (vs. monoecious), taller (to 4 m vs. less than 2 m) plants, longer (vs. shorter) inflorescence, and unique shape of fruits, and differs from the latter mainly by its taller (to 4 m vs. less than 2 m) plants, late and longer (Jun. to Oct. vs. Mar. to Apr.) flowering time, longer (6–20 mm vs. 5–12 mm) pedicel, 6 (vs. 4) tepals of pistillate flower and 3 (vs. 4)-loculed ovary (Table 3, Fig. 3).

Table 3.
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Morphological comparison of Begonia giganticaulis, B. longifolia and B. acetosella.

Character B. giganticaulis B. longifolia B. acetosella
Plant
sexuality dioecious monoecious dioecious
height (m) up to 4 less than 2 less than 2
Petiole length (cm) 0.7–7 1–12 1–10
Leaf blade surface muriculate glabrous to less muriculate muriculate to hirsutulous
Inflorescence
peduncle length (mm) 7–15 4–10 2–10
flower number 1–11 1–11(15) 1–3(5)
Tepal number of pistillate flower 6 6 4
Tepal colour pinkish to white white pinkish to white
Ovary 3-loculed 3-loculed 4-loculed
Pedicel length (mm)
male flower 10–20 5–12 8–12
female flower 6–12 5–12 5–10
Fruit horn or wing none to rarely short crest none to short crest or horns short to long horns or wings
Flowering time June-October June-December March-April

Description

Herb perennial, evergreen, to 4 m tall, dioecious. Rhizome short, stout, nearly unbranched, reddish brown, to 12 cm thick. Stem erect, reddish brown or green, glabrous, internodes to 5 cm thick, with many longitudinally fusiform whitish spots, cross section of stem often reddish brown, nodes notably enlarged, to 7 cm thick, with unequally oval to round whitish spots, many shrubby branches on the upper part of main stem. Stipule long-triangular, light green or pinkish green, 9–25 × 2–8 mm, glabrous, margin entire, dorsal ridge pinkish, apex acuminate with arista 4–6 mm long. Petioles green, pink to red, glabrous, 7–22 cm long, 1–3 mm thick. Leaf blade ovate-lanceolate to lanceolate, 4–19 × 0.8–8 cm, adaxial green, muriculate to nearly glabrous, adaxial veins slightly concave; abaxial greyish green, veins usually red, convex, main veins sparsely and obliquely strigose; base obliquely cordate, margin shallowly and remotely denticulate, apex long caudate; Inflorescence dichasial cyme, axillary, short, 3–5 cm long, unbranched to branched once, rachis glabrous, green, pinkish green to red, base usually red-brown, 7–15 mm long, 1–1.5 mm thick, 3–11 male flowers or 1–5 female per inflorescence. Bract often caducous, pinkish green, long triangular, glabrous, ca. 6 × 3 mm, apex acuminate; bracteoles smaller. Staminate flower: pedicel glabrous, white, whitish or pinkish green, 10–14 mm long, ca.1 mm thick; corolla 18–24 mm in diameter; tepals 4, subequal, glabrous, outer 2, obovate, 9–14 × 6–9 mm, apex obtuse, adaxially white and middle-upper part abaxially pink, or pure white for some individuals, longitudinal veins unapparent; inner 2, pure white, obovate to obovate-lanceolate, 8–13 × 5–7 mm, apex obtuse; androecium nearly actinomorphic, ca. 5 mm long, 6–7 mm in diam; stamens 48–60, filaments free, 1–2 mm long; anther yellow, 2–3 mm long, apex obtuse or nearly so. Pistillate flower: pedicel white or green-white, 6–12 mm long, 0.8–1 mm thick; corolla 20–25 mm, tepals 6, rarely 4, glabrous, outer 3 (rarely 2), obovate or long obovate, thick and rigid, 12–18 × 7–10 mm, adaxial surface nearly white, distinctly concave, abaxially pink on middle-upper part, inner 3 (rarely 2), obovate-lanceolate to oblanceolate or long elliptical, slightly narrower than outer tepals, 10–19 × 6–8 mm, white, glabrous, apex obtuse; styles + stigmas 5 mm long, 7–8 mm wide; styles 3, free; stigmas yellow, nearly U-shaped, each side spirally twisted 1.5 circles; ovary pink or green, with white convex spots; placentation axile, 3-loculed, each placenta 2-branched. Peduncle green to pinkish green, glabrous, 8–12 mm long, ca. 1 mm thick. Fruit red, pink or green, glabrous, triangular-gyroscopic, 8–11 × 1–12 mm wide, concave between two placentas, wingless to occasionally short ridged, apex with beak 3–4 mm long. Flowering Jun.–Oct., fruiting Jul.–Dec.

Figure 4. 

Illustration of Begonia giganticaulis D.K.Tian & W.G.Wang, sp. nov. (Drawn by Mr. Zhi-Min Li) A male flowering branches B female flowering branches C main stem line spots, much expanded node and internode base D expanded node and internode base on small upper branches E leaf blade F leaf (abaxial), showing sparse hairs on veins G stipule H staminate flowers I, J pistillate flower K side view of androecium L stamens M ovary and stigmas N fruit O dissection of ovary showing placentae.

Additional specimen examined

China. Xizang: Mêdog County (墨脱县), Beibeng Town (背崩乡), Baimu Xiri River (白母西日河), forest slope of river valley or water’s edge along stream, 29°21'9"N, 95°11'21"E, elev. 1320 m, 10 September 2020, Dai-Ke Tian, Fang Wen, Qing-Gong Mao, & Zhu Lu TDK4773-B (paratype CSH!, ♂); 29°20'0"N, 95°10'49"E, elev. 1110 m, 10 September 2020, Dai-Ke Tian, Fang Wen, Qing-Gong Mao, & Zhu Lu TDK4765-A, TDK4765-B, (paratype CSH!); 29°18'32"N, 95°10'38"E, elev. 980 m, 10 September 2020, Dai-Ke Tian, Fang Wen, Qing-Gong Mao, & Zhu Lu TDK4777 (paratype CSH!); near Ani Bridge (阿尼桥), 29°17'8.41"N, 95°10'3.23"E, elev. 810 m, 3 July 2020, Wen-Guang Wang, You-Yun Li, Xing-Da Ma, & Jian-Yong Shen, WWG 2014 (paratype, HITBC!), WWG 2015 (paratype HITBC!); elev. 1100 m, 16 September 1974, anonymous 2608 (paratype PE!); elev. 800–1400 m, 30 June 1980, Wei-Lie Chen 10809 (PE!); near No. 2 Bridge, 29°16'42"N, 95°10'49"E, elev. 810 m, 1 October 2017, Dai-Ke Tian, Yan Xiao, Xin Zhong, Li-Zhi Tian & Zhu Lu TDK3429 (paratype CSH!); Beibeng to Hanmi (汗密), elev. 840 m, 7 August 2010, South Tibet Expedition Team (藏南队), Xiao-Hua Jin, Shu-Dong Zhang, Zhong-Yang Li, Bao-Cheng Wu, Xian-Yun Mu, Jing Li & Wei-Tao Jin, STET2304 (paratype PE!); Hanmi to Maniweng (马尼翁), elev. 800–1000 m, 6 August 1974, Qingzang Team 74-4114 (paratype PE!); elev. 1200 m, 24 June 1983, Bo-Sheng Li & Shu-Zhi Chen 05229 (paratype PE!); Maniweng to Ani Bridge, elev. 700–1000 m, 3 August 1972, Tibet Expedition Team, Institute of Biology 1631 (paratype HNWP!).

Distribution and habitat

Currently known from at least two localities in Mêdog, southern Xizang (Tibet), China (Fig. 5). It grows on the slopes under forest along streams, elevation 450–1400 m.

Figure 5. 

Distribution of B. giganticaulis (triangles) from southern Xizang, China.

Conservation status

Begonia giganticaulis is currently found in at least two localities in Mêdog of Tibet. Additional populations might be discovered when more surveys are conducted in China-India border region. However, based on current data, it should be categorised as Endangered: B2a (IUCN 2019) due to < 500 km2 area of occupancy with severely fragmented habitat consisting of < 5 known populations totally under 1000 individuals by estimation.

Etymology

The specific epithet refers to the huge (very tall and thick stem) plant size of the new species, which is the tallest begonia in Asia.

Molecular systematic relationship

We obtained 12 nrITS, 13 rpL16 intron, and 13 ndhA intron of the new species and related Begonia taxa. In order to reconstruct the phylogenetic relationship of the new species, 13 taxa within sect. Platycentrum were included and B. cavaleriei from sect. Coelocentrum was selected as outgroup. In total, the matrix was composed of 26 accessions and contained the 962 bp rpL16 intron, the 1109 bp ndhA intron and the 672 bp nrITS sequence. Of the total 2743 characters, 132 were parsimony informative.

Based on MP analysis, the new species was clustered with B. acetosella and B. acetosella var. hirtifolia (Fig. 6A), while it was clustered with B. longifolia under BI analysis (Fig. 6B). Both MP and BI analyses showed that all five individuals of the new species were clustered together and separated from other taxa (Fig. 6A, BS: 100%; Fig. 6B, PP:1.00).

Figure 6. 

Phylogenetic tree inferred by MP A and BI B analyses based on the combined matrix of two plastid loci (rpL16 intron and ndhA intron) and nuclear ITS. Maximum parsimony bootstrap A and Bayesian inference posterior probability values B are labelled on the branches; when the number is below 80 and 0.80 in maximum parsimony bootstrap and Bayesian inference posterior probability, respectively, the branches are labelled—.

Notes. – The earliest specimen of Begonia giganticaulis was collected in 1972 between Maliweng and Ani Bridge, Mêdog, Tibet, China. This species is similar to B. acetosella in appearance when its flowers are unavailable for observation, therefore, it was misidentified (24 June 1983, Bo-Sheng Li & Shu-Zhi Chen 05229, PE! was wrongly identified as B. acetosella by C.Z. Gu in March 2004). Also, due to its high similarity to B. longifolia particularly in morphology of flowers and fruits, B. giganticaulis was wrongly labelled as B. longifolia by Morris (2010) who found this species in southern Mêdog county.

Acknowledgements

The study was supported by the funds from National Natural Science Foundation of China (31570199, 31860048), the Second Tibetan Plateau Scientific Expedition and Research (STEP) Program (2019QZKK0502), and Shanghai Administration Bureau of Landscape and City Appearance (F122416, G202401). The authors thank Dr. Qing-Gong Mao, Dr. Fang Wen, Mr. Li-Zhi Tian, Mr. Zhu Lu, Mr. Jian-Yong Shen, Mr. Xing-Da Ma and Mr. You-Yun Li, for supporting field survey, and Shi-Wei Guo for providing partial photos for use. The specimens from the Institute of Botany, Chinese Academy of Sciences were reviewed through Chinese Virtual Herbarium.

Reference

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