Trigonostemon eberhardtii Gagnep., Bull. Soc. Bot.

S., Wangchuk, D., Tshering & Thukten, K., 2024, Trigonostemon (Euphorbiaceae): A new generic record for the Flora of Bhutan, Rheedea 34 (3), pp. 211-213 : 211-213

Trigonostemon eberhardtii Gagnep., Bull. Soc. Bot. France 69: 749. 1923. Lectotype (designated by Yu & Van Welzen, 2020): VIETNAM, Annam ,

Thanh-hoa, Bon 5239 [P00717103 digital image!].

Fig. 1

venation tri-nerved from the base, midrib slightly raised above and distinctively elevated beneath,

other secondary veins 4–7 pairs, convergent, tertiary veins scalariform, veinlets reticulate.

Inflorescences bisexual, terminal or axillary,

paniculate; main axis terete, up to 20 cm long, pubescent to glabrous; bracts linear to lanceolate to triangular, 0.7–2.7 × 0.3–0.6 mm, pubescent outside; bracteoles linear to lanceolate, 0.4–0.7 × 0.1–0.2 mm, densely pubescent. Inflorescences bisexual, terminal or axillary, paniculate; main axis terete, up to 30 cm long, pubescent to glabrous; bracts linear to lanceolate to triangular,

c. 0.7 × 0.6 mm, pubescent outside, bracteoles linear to lanceolate, 0.4–0.7 × 0.1–0.2 mm, densely pubescent. Staminate flowers 6–8 mm

in diam.; pedicels c. 2 cm long, glabrous; sepals elliptic, c. 6 mm long, base connate, margin entire, apex acute, pubescent outside; petals Shrubs, 1–5 m tall; bark dark to pale-brown or greyish brown. Stipules subulate, 0.3–0.7 mm

long, caducous. Leaves, alternate; petiole terete, grooved or flat above, up to 5 cm long, glabrous or pubescent; lamina elliptic, 5–21 × 2–10 cm,

chartaceous, base acute-cuneate, two adaxial glands present, margin entire or very distantly crenulate, apex acuminate to caudate, upper surface glabrous, dark green, lower surface sparsely pubescent along veins, pale green; obovate, c. 5 × 5 mm, contort, white, lower part cuneately narrowed, apex rounded, glabrous; stamens 3, stamen c. 1.5 mm long, white, filament free part c. 0.2 mm long. Pistillate flowers 1 cm

in diam.; buds conical; pedicels slightly thickened toward apex, c. 9 mm long, glabrescent; sepals elliptic c. 9 mm long, accrescent in fruit; petals as in staminate flowers; ovary 1 mm in diam., glabrous, green, style 0.1–0.2 mm long, stigmas

0.8–1.1 mm long, bent outward, white, apically slightly thickened and slightly bifid. Fruits c. 18 mm in diam., greenish, glabrous, pedicle up to 2

cm long.

Flowering & fruiting: Flowering and fruiting from March to December.

Habitat & ecology: The species in Bhutan is found along riverbanks in silty-loamy soil associated with limestone outcrops in subtropical forests.

Associated plant species include Crateva religiosa G. Forst. , Flueggea virosa (Roxb. ex Willd.) Royle ,

Clerodendrum infortunatum L., Bergera koenigii L.,

and Litsea sp. Distribution: China, Thailand, Laos, Cambodia, Vietnam and now in Bhutan.

Specimen examined: BHUTAN, Tsirang, Balwani , N 26 0 54 ’43.191’’ E 90 0 1 ’ 56.154’’, 203 m, 14.05.2023

Sangay Wangchuk SN 01080 (THIM [15871]); ibid.,

14.05.2023, Sangay Wangchuk SN 0592 (The Ugyen

Wangchuck Institute for Forestry Research and

Training Herbarium).

Notes: This is a new generic and species record for the Flora of Bhutan, and the distribution extension of the genus Trigonostemon till the foothills of the Himalayas. The genus can be easily distinguished from the other members of the subfamily Crotonoideae by its bright, colourful petals, as suggested by Balakrishnan and Chakrabarty (1991), and by its 3 or 5 connate stamens ( Yu, 1989). Morphologically, T. eberhardtii resembles T. viridissimus (Kurz) Airy Shaw , but it can be differentiated through its monopodial inflorescence branching pattern, white petals, and indistinctive style ( Yu & Van Welzen, 2020).

Figures

Fig. 1. Image of a specimen of Trigonostemon eberhardtii Gagnep. deposited at the herbarium of Ugyen Wangchuck Institute for Forestry Research and Training.