Begonia fimbristipula subsp. siamensis (sect. Diploclinium, Begoniaceae), a new taxon of the megadiverse genus endemic to Thailand Author Radbouchoom, Sirilak https://orcid.org/0000-0002-6027-7832 Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, Yunnan, China & University of Chinese Academy of Sciences, Beijing 100049, China Author Phutthai, Thamarat Faculty of Environment and Resource Studies, Mahidol University (Salaya Campus), Nakhon Pathom 73170, Thailand thamarat.phu@mahidol.edu Author Schneider, Harald https://orcid.org/0000-0002-4548-7268 Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, Yunnan, China harald@xtbg.ac.cn text PhytoKeys 2023 2023-01-10 218 1 10 http://dx.doi.org/10.3897/phytokeys.218.85699 journal article http://dx.doi.org/10.3897/phytokeys.218.85699 1314-2003-218-1 3799E74E0B7F50469318CB9BE539E071 Begonia fimbristipula Hance subsp. siamensis Phutthai & S.Radbouchoom subsp. nov. Figs 1 , 2 Type . Thailand • Phitsanulok Province , Nakornthai , Phu Hin Rong Kla national park , Lan Hin Pum rout; 1300 m a.s.l. ; 29 Oct. 2001 ; S. Watthana , P. Suksathan 1570; herb on sand stone rather shed and wet; ( holotype QBG! 21778, isotype BKF! SN187939 ) . Description. Perennial monoecious acaulescent herb, 10-25 cm tall. Tuber globose or sub-elongate 0.7-2.0 cm long, with fibrous roots. Leaves 1-3; petiole maroon, 9.0-13.5 cm long, densely red villous and pubescent; lamina basifixed, succulent, broadly ovate, symmetric or slightly asymmetric, adaxial surface green, sometimes sparsely white spotted, densely villous, conspicuous dark green band 2-3 mm wide along the midrib, secondary and tertiary veins, abaxial surface green or red, densely red villous, conspicuous maroon band 2-3 mm wide along the secondary and tertiary veins, 6.5-15 x 4.6-12 cm, base cordate, margin denticulate and ciliate, apex acuminate, venation palmate-pinnate, primary veins 6-7, secondary veins branching dichotomous 2-4, prominent beneath. Stipules , ovate-triangular, apex acute, margin ciliate, 2.0-3.0 x 1.2-1.7 mm, red villous. Inflorescences arising directly from tuber, bisexual, cymose, branching 1-3 times; peduncles maroon, 11.5-25 cm long, sparsely red villous; bracts soon falling, membranaceous, oblong, glabrous, apex obtuse, margin fimbriae. Staminate flowers : pedicel maroon, 1.5-2.0 cm long, glabrous, erect; tepals 4, white-pinkish to pink with the pale pink flash at the centre, glabrous both sides; outer 2 ovate to suborbicular, 0.8-1.0 x 0.3-0.5 cm, base rounded to cuneate, margin entire, apex obtuse to rounded; inner 2 narrowly elliptic or lanceolate-elliptic, 0.7-1.2 x 0.7-1.0 cm, base cuneate, margin entire, apex obtuse to rounded; androecium zygomorphic; stamens 10-25, yellow; filaments fused at base, c.1.0 mm long; anthers clavate, apex rounded, 0.3-1.0 mm long, basifixed, dehiscing by 2 short slits. Pistillate flowers : pedicel maroon, 1.5-2.0 cm long, tepals 5, white-pinkish to pink with a pale pink flash at the centre, glabrous both sides; outer 3, ovate-broadly ovate, 0.7-1 x 0.3-0.4 cm, apex obtuse to rounded, margin entire, base cuneate; inner 2, ovate to lanceolate-elliptic, 0.6-0.9 x 0.3-0.6 cm, apex obtuse to rounded, margin entire, base cuneate; styles 3, yellow, fused at base 1.0-2.0 mm long, bilobed, crescent-shaped, spirally twisted; ovary with 3 unequal wings, oblong, 0.5-1.0 x 0.4-0.6 cm, glabrous; placentation axile, placentae bilamellate, locules 3. Fruit oblong, unequally 3 winged, capsule, nodding, pink to pale green, 1.0-2.2 x 0.9-1.1 cm included wings, abaxial wing falcate or elliptic, extended 1.0-1.3 x 0.7-0.9 cm, wider than lateral wings, lateral wings, narrowly triangular, 0.7-1 x 0.2-0.3 cm. Habitat. The new taxon is currently known from seven collections obtained from three provinces located in northern and north-eastern Thailand (Fig. 2 ), where it grows on both limestone and sandstone outcrops in evergreen forest at high elevation (1300-1900 m). Individuals growing on limestone rocks are distinct from individuals growing on sandstone rocks by the presence of a dense indumentum formed by red trichomes. The indumentum of individuals growing on sandstone is less dense and the trichomes have a brighter colour. Accessions of Begonia fimbristipula subsp. siamensis show high phenotypic variation among individuals of the same population especially in leaf size and abaxial leaf surface colour (Fig. 1H, H '). The notable phenotypic disparity resembles reports from occurrences of B. fimbristipula subsp. fimbristipula in southern China ( Wang et al. 2016 ; Tian et al. 2018 ). Phenotypic plasticity has been considered to result from adaption to the harsh environments occupied by these plants ( Wang et al. 2016 ). Figure 1. Begonia fimbristipula Hance subsp. siamensis Phutthai & S.Radbouchoom subsp. nov. A habitat B habit C tuber globose C ' tuber sub-elongate D peduncle E petiole F leaf adaxial and abaxial surface F ' close-up of white spots on adaxial surface of leaf G close-up of trichome on adaxial surface of greenish leaf G ' close-up of trichome on abaxial surface of leaf H close-up of abaxial surface of reddish leaf H ' close-up of abaxial surface of reddish leaf I staminate flower visualised using face view, side view, back view J pistillate flower visualised using face view, side view K fruit L cross sections of young ovary in the sequence top, middle and bottom. Figure 2. Distribution of B. fimbristipula Hance subsp. siamensis Phutthai & S.Radbouchoom subsp. nov. (red triangle) and B. fimbristipula Hance subsp. fimbristipula (blue circle). Phenology. Flowering Time: June-September; Fruiting Time: August-December. Etymology. The subspecific epithet siamensis alludes to the nativity of this taxon to "Siam" , the exonym that was used for Thailand before 1949. Conservation assessment. The recorded occurrences of the new subspecies were mostly obtained in protected areas, e.g. National Parks. The high protection is arguably reduced by threats caused by tourism activities. In Phisanulok province, this species creates a beautiful landscape by growing on the sandstone cliff along the trekking trail, which is a famous spot among tourists. Some of its populations are outside the protected area where the new taxon has been threatened by illegal trade in wild ornamental plants, and habitat infringement. Until now, there is still no conservation plan for the new subspecies at any of these localities. Further surveys are arguably required to obtain a more accurate description of the distribution of this species in Thailand but also in Laos, Myanmar and Vietnam. The currently known area of occupancy (AOO) has been estimated as 32 km2 ( Bachman et al. 2011 ; http://geocat.kew.org/). Based on IUCN criteria, the status assigned is "Vulnerable" (VU: B2 a, c (iii, iv); C2 (ai, ii)) ( IUCN 2019 ). Additional specimens examined. Thailand - Chiang Mai Prov. • Pang Hin Fon , Mae Chaem District ; 1300 m a.s.l. ; 09 June 2017 ; W. Pongamornkul 6422; herb 20 cm high in dry evergreen forest, flowers pink; QBG 105946 • Dong Yen , Doi Chiang Dao ; 1900 m a.s.l. ; 20 Nov. 1999 ; P. Suksathan 2134; on mossy rock in shade; QBG16461 . - Phitsanulok Prov. • Phu Hin Rong Kla national park ; 1300-1600 m a.s.l. ; 22 Jan. 2005 ; O. Kudjabnak , D. Watanachaiyingcharoen BRT (NU) 0046; herb on sand-stone; BKF SN152894 . - Nan Prov. • Doi Phu Kha National Park , hill evergreen forest; 19°13'N , 101°06'E ; 1750 m a.s.l. ; 26 July 1999 ; P. Srisanga 918; herb on rock, leaves dark greenish-red, flower pink, stamen and stigma yellow; QBG15203 • ibid, Pua ; 19°10'N , 101°07'E ; 1800 m a.s.l. ; 31 Aug. 2000 ; P. Srisanga 1533; hill evergreen forest, herb on rock, leaves greenish red, stem and pedicel red; QBG17980 ; BKF SN193126 • ibid, trail from Lan Doo Dao Phatang ; 1700 m a.s.l. ; 26 June 2008 ; R. Pooma , M. Tamura 7104; on moist rock surfaces, densely mosses, lower montane forest; BKF SN188535 • Doi Pha Phung , Nam Tok , Na Noi District ; 18°24'22.06"N , 100°32'50.24"E ; 992 m a.s.l. ; 18 December 2018 ; P. Phaosrichai , M. Wongnak , S. Wongwan , S. Sitthisuk 1265; herb about 20 cm high, fruit brownish-red; QBG112488 . Specimens examined of Begonia fimbristipula Hance subsp. fimbristipula . China - Fujian Prov. • Wuyishan , on the way from ticketing entrance to Tienyoufeng ; 270 m a.s.l. ; 30 May 1997 ; Ching-I Peng 16885; HAST132046 . - Guangdong Prov. • Ding-hu Shan ; 06 May 1882 ; C. Ford 6; isolectotype K K000251078 • ibid; 150 m a.s.l. ; 15 Apr. 1964 ; K.C. Ting , K.L. Shi 1402; BKF SN006485 • ibid; 6 May 1928 ; W.Y. Chun 6393; E E00299226 • ibid, Qingyuan Shi , Liannan Xian , Dalongshan Forest Plantation ; 310 m a.s.l. ; 4 Apr. 2005 ; Ching-I Peng 19496; on mossy rocky slope; HAST122379 • ibid; 26 May 1918 ; C.O. Levine 2027; E E00299227 • South of Ping Yung ; 60-175 m a.s.l. ; June 1924 ; R.C. Ching 2002; P P06844316 . - Guangxi Prov. • Zhuangzu Zizhiqu , Laibin Shi , Jinxiou Yiaozu Zizhixian , Dayiaoshan national nature reserve; 1200 m a.s.l. ; 18 September 2003 ; Wai-Chao Leong 3673; on mossy rock face, mixed Cathaya and broadleaf forest; HAST 97112 .