Begonia giganticaulis D.K.Tian & W.G.Wang, 2021

Tian, Dai-Ke, Wang, Wen-Guang, Dong, Li-Na, Xiao, Yan, Zheng, Min-Min & Ge, Bin-Jie, 2021, A new species (Begonia giganticaulis) of Begoniaceae from southern Xizang (Tibet) of China, PhytoKeys 187, pp. 189-205 : 189

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

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, ♀)

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 ).

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.

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.

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.

Figures

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).

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.

Figure 5. Distribution of B. giganticaulis (triangles) from southern Xizang, China.