Trigonostemon flavidus Gagnep.

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 33

9. Trigonostemon flavidus Gagnep. — sect. Trigonostemon — Fig. 2 ; Map 7

Trigonostemon flavidus Gagnep.(1922) 749; (1925b) 320;P.T. Li et al. (2006) 119;P.T. Li & M.G. Gilbert (2008) 273;R.Y. Yu & Welzen (2018) 195. — Lectotype (designated here): Harmand 3273 (P, barcode P00717104 ; iso P, barcode P00717105 ), Laos, in Lakhon mountains , near Me-Kong.

Trigonostemon heterophyllus Merr. (1930) 38; N.P. Balakr. & Chakrab. (1991) 617,f.5;H.S. Kiu (1996) 163; Chantar. (2005) 24;(2007)577,pl.31,1. — Type: Tsang 594 [17343] (A*, barcodes A00048861 , A00048862 ,B*, barcode B10 0249526, BM, barcode BM000951501 , BO, sheet no. BO1695956 , CAL, barcode CAL0000023662 , ECON*, barcode ECON00254237 , G, barcode G00435104 ,K,barcode K000959339 ,L, barcode L0160156 , MO*,barcode MO-260398, NTUF*, NY*, barcode NY00273341 , P, barcode P00717108 , PE, barcodes PE00022683 , PE00022684 , UC*, barcode UC373861 , US*, barcodes US 00096533,US00997745,W*,sheet no. W1940-0006789 ,WIS*, barcode WISv0255641), China, Hainan, Taam Chau District [= Danzhou County], Sha Po Shan [= Mt Sha Bao].

Trigonostemon sunirmalii Chakrab. & N.P.Balakr. (1984b) 179. — Type: Biswas 22 (holo CAL, barcode CAL0000023663 ; iso CAL, barcode CAL0000023664 ), Myanmar, Tenasserim [= Tanintharyi Region], Nim- chaung.

Small trees, 1–2.5 m tall; flowering branches up to 4.5 mm diam, densely pubescent. Outer bark 0.1–0.2 mm thick, pale brown to dark grey, smooth or roughened; inner bark 0.1–0.2 mm thick, reddish brown; wood pale yellow. Stipules subulate, 0.7–1 mm long, pubescent at base. Leaves: petiole terete but sometimes flattened or grooved above, 0.2–1.2 cm long, 0.7–2.4 mm diam, densely pubescent; blade obovate or oblanceolate, cu- neately narrowed and sometimes unequal in the lower middle part, 9–35 by 5–9 cm, chartaceous, base abruptly rounded to truncate, with 2 adaxial glands, margin distantly serrate, teeth small and nipple-like, apex caudate to acuminate, upper surface dark to light green, lower surface paler, both surfaces pubescent, especially on secondary veins and margin; vena- tion pinnate; midrib thin, elevated on both surfaces, secondary veins 10–13 pairs, tertiary veins reticulate, often obscure. Inflorescences bisexual, in short cymes or thyrses, cauliflorous or supported by a peduncle and involucral bracts; peduncle 1–9 cm long, pubescent; involucral bracts lanceolate, 8–38 by 0.7–9 mm, pubescent; bracts lanceolate to linear, 1.1–5.5(–15) by 0.2–0.7(–2) mm, pubescent. Staminate flowers 3.6–6 mm diam; pedicel 2.4–4.7 mm long, 0.15–0.3 mm thick, pink to light green, glabrous; sepals elliptic or obovate, 1.1–2.4 by 0.5–1.8 mm, green, base connate, margin ciliate, apex often acute to rounded, occasionally with a notch, pubescent outside; petals obovate, 2.1–4.2 by 1.7–2.2 mm, base claw-like, apex rounded, glabrous, dark reddish to maroon-purple to black; disc lobes obovate or rectangular, 0.4–0.7 by 0.15–0.25 mm, sometimes narrowed at base, often reflected at apex, light orange, gla- brous; stamens 3, androphore 1–1.2 mm long, c. 0.1 mm diam, white, shortly trifid at apex, free part of filaments 0.1–0.2 mm long; anthers free, divaricate at apex, thecae 0.4–0.6 mm long, pale yellow, connective pinkish red, with numerous droplets with secretion. Pistillate flowers few, slightly enlarged when fruiting, up to c. 1 cm diam; pedicel c. 1.5 mm long and c. 0.5 mm diam in flower bud, accrescent to c. 7 mm long and apically c. 1 mm diam when fruiting; sepals lanceolate to linear, 2.2–3.4 by 1–1.5 mm when flowering, accrescent to 2.4 by 0.9 cm in fruit, margin entire or with a few teeth, apex acuminate, pubescent outside; petals elliptic, 3–3.3 by 2–2.7 mm (flower bud), caducous; disc glands rectangular to semi-orbicular, 0.5–0.6 by 0.4–0.6 mm, rounded or truncate at apex, glabrous; ovary c. 0.7 mm diam, bright dark green, densely pubescent, style almost indistinct, stigmas 3, completely divided, free arms 0.6–0.7 mm long. Fruits c. 1.2 cm diam, green when young, brown when mature, densely pubescent; wall woody, 0.5–0.55 mm thick; columella 4.2–6.7 mm long. Seeds 4.2–6.7 by 4.5–5.7 mm, light or dark brownish when dry, hilum irregularly shaped, more or less triangular, 0.8–1.3 by 0.5–0.7 mm diam.

Distribution — Myanmar (Tenasserim), China, Laos, Thai- land, Malay Peninsula.

Habitat & Ecology — Understorey in evergreen forests to deciduous hardwood or bamboo forests, often near rivers, growing on sandstones to conglomerate bedrocks. Elevation: c. 200 m. Flowering: January to March, July; fruiting: February, July to October.

Note — Trigonostemon flavidus strongly resembles T. semperflorens (Roxb.) Müll.Arg. from India but has much denser and stronger hairs (Yu & Van Welzen 2018, Balakrishnan & Chakra- barty 1991). We treat them as separate species, because there is a clear gap in the extent of pubescence (pubescent in T. flavidus but glabrous in T. semperflorens ; no intermediate forms are found) and there is a gap in the distribution – both species are absent in central Myanmar ( T. flavidus has its western most limit in S Myanmar (Tenasserim) and T. semperflorens occurs in NE India and Bangladesh).

Figures

Map 7 Distribution of Trigonostemon flavidus Gagnep. (X) and T. semperflorens (Roxb.) Müll.Arg. (▲).

Fig. 2 Trigonostemon flavidus Gagnep., cultivated in South China Botanical Garden. a. Growing habit; b. bark; c. cauliflorous staminate inflorescences; d. lateral view of staminate flowers; e. top view of staminate flower; f. back view of staminate flower; g. young pistillate flowers and mature fruit; h. young fruit; i. staminate flower with 4 stamens (abnormal growth). — Photos by Ren-Yong Yu.