Begonia tenasserimensis Phutthai & M. Hughes, 2017

Begonia tenasserimensis Phutthai & M. Hughes View in CoL , sp. nov. — Fig. 1 View Fig ; Map 1 View Map 1

Begonia tenasserimensis is vegetatively similar to and shares the presence of persistent tepals when the fruit matures with B. crenata Dryand. , but differs from that species in having an acutely lobed leaf lamina with 3 main veins (vs unlobed with 5 main veins) and a shortly spinose dentate leaf margin (vs crenate), pistillate flowers with 5 tepals (vs 6) and staminate flowers with lanceolate inner tepals (vs broadly elliptic), and a more branched inflorescence. — Type: D. J. Middleton, K. Bunpha, P. Karaket , S. Lindsay , T. Phutthai , S. Suddee & N. Tetsana 5371 (holo E, barcode E00596936 ; iso BKF, PSU), Thailand, Satun, Thung Wa District , on eroded limestone with numerous pools and small waterfalls in deep shade gallery forest, N7°06'40" E99°50'36", 140 m, 10 Sept. 2010 GoogleMaps .

Etymology. The specific epithet ‘ tenasserimensis ’ is derived from the

Tenasserim Range to where the species is endemic.

1 Faculty of Environment and Resource Studies,Mahidol University (Salaya campus), Nakhon Pathom 73170, Thailand; corresponding author e-mail: thamarat.phu@mahidol.ac.th.

2 Royal Botanic Garden Edinburgh, 20 A Inverleith Row, Edinburgh, EH3 5 LR, Scotland, UK .

Monoecious herb, 5–20 cm tall. Stems succulent, glossy, erect, glabrous, pale green or dark red; tubers globose or subglo- bose, 5–10 mm diam, with numerous fibrous roots. Stipules persistent, lanceolate, pale green 4 by 3 mm, with sparse glandular hairs. Leaves 3–5 per plant, basifixed, petiole pale green or maroon, reddish brown when dry, 1–5 cm long; leaf blade succulent, symmetric or subsymmetric, chartaceous when dry, adaxial surface sparsely hirsute, light green, glossy, iridescent, abaxially glabrous and glaucous; palmatifid, 4–7 by 4– 8 cm, apex shallowly trilobed, margin dentate or biserrate with short spinose hairs, base truncate or rarely cordate; vena- tion palmate, main veins 3. Inflorescences terminal, 5–9 cm long, a compound dichasium, bisexual, 1–4 times branched with many staminate flowers and 1 pistillate flower per branch on the lowest branch, protandrous; peduncles 2–7 cm long, terete with glandular hairs, pale green or dark red, glossy. Bracts persistent, membranous, pale green, glossy, lanceolate, with sparse glandular hairs, 2–3 by 1–2 mm, apex obtuse, margin entire. Staminate flowers: pedicels 4–5 mm, erect, with glandu- lar hairs; tepals 4, pale magenta, outer 2 suborbicular, 4–6 by 4–5 mm, base rounded, apex obtuse, margin entire, glabrous on both sides; inner 2 lanceolate, 3–4 by 2–3 mm, base obtuse, apex acute, margin entire, glabrous on both sides; androecium zygomorphic, like bunch of bananas, stamens c. 18–20, yellow, filaments c. 0.5 mm long, anthers oblong c. 1 mm long, apex retuse, dehiscing by slits near the tip, filaments fused in a col- umn. Pistillate flowers: pedicels erect, pale magenta, 3–10 mm long; tepals 5, unequal, pale magenta, outer 2 orbicular, 4–6 by 4–5 mm, apex obtuse, margin entire, base rounded, gla- brous on both sides; inner 3 lanceolate or oblong, 3–4 by 2–3 mm, apex acute, margin entire, base obtuse, glabrous on both side; styles 3, fused halfway, yellow, stigmatic band irregularly crescent-shaped; ovary with 3 wings, with glandular hairs, 2-locular, placenta bilamellate. Fruits with persistent tepals, glossy, pale green, pendulous, drying pale brown, c. 5–6 by 5–10 mm; locule elliptic, 3–4 by 3–5 mm, abaxial wing facing down, slightly larger than the lateral wings, 5–10 mm long. Seeds numerous, brown, barrel-shaped, c. 0.3 mm long.

Distribution & Ecology — Peninsular Thailand (Satun Prov- ince, Thung Wa, Than Plew Waterfall, 140 m; Ranong Province, Raksra Warin hot water spring park, 100 m) and Myanmar (Tenasserim), in small crevices on eroded limestone rocks amongst numerous pools and small waterfalls in gallery forest. Flowering: July to November; fruiting: November to December.

Conservation assessment — Begonia tenasserimensis is known only from two karst limestone localities in Thailand and one in Myanmar, the latter collected in 1861. Only 25 % of the 20,000 km 2 of karst limestone in Thailand is protected (Cle- ments et al. 2006). The Thai populations of the species are in localities classed as recreation areas (IUCN protected area category VI; an area which is promoted for sustainable use, where conservation and sustainable use can be mutually beneficial; IUCN 2016) and can receive many tourist visitors in the high season. The exact locality of the Myanmar collection is unknown. We consider a category of Vulnerable (VU D2) to be appropriate, as the populations are prone to the effects of human activities or stochastic events within a very short period ( IUCN 2012).

Additional specimens examined. MYANMAR, Tenasserim, J.W. Helfer 2584

(K), 1861–2. – THAILAND, Ranong, C. Phengklai 1300 ( BKF) , 18 Sept. 1968.