Trigonostemon montanus R.Y.Yu & Welzen, 2020

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 38-40

19. Trigonostemon montanus R.Y.Yu & Welzen , sp. nov. — sect. Tylosepalum — Fig. 3 ; Map 6

Trigonostemon montanus R.Y.Yu & Welzen resembles T. lii Y.T.Chang in the oblong leaves, which remain green when dry, but differs in having shorter and dichotomously branching inflorescences. ― Type: Koelz 27903 (holo L, barcode L.2260526), India, Assam, Cachar , Laikul , 6 000 ft, 6 May 1951. Paratypes: Koelz 27849 ( L, barcode L.2260525), India, Assam, Cachar, Laikul , 4 000 ft, 1 May 1951 ; Bor 2783 ( K), India, Assam, Naga Hill , 5 000 ft, 26 Apr. 1935 .

Shrubs, 1.8–2.4 m tall; flowering branches 1–1.6 mm diam, pubescent when young, glabrous in old parts. Outer bark c. 0.1 mm thick, pale brown to grey; inner bark 0.1–0.2 mm thick, white or very light green when young, sap not seen; wood white. Stipules subulate, 0.2–0.4 mm long, caducous, often pubescent at base. Leaves: petiole terete but grooved above, 0.35–1 cm long, 0.7–1.5 mm diam, slightly pubescent when young, glabrescent; blade oblong, 6.2–11.8 by 1.4–2.7 cm, chartaceous, base acute, 2 adaxial glands present, margin entire or distantly serrate, teeth glandular, apex caudate, both surfaces glabrous but lower pubescent when young; venation triplinerved, slightly pubescent beneath, midrib slightly raised above and elevated beneath, secondary veins 5–7 pairs, bow-shaped and connected along margin, tertiary veins scalariform, veinlets reticulate, obscure. Inflorescences bisexual, terminal or subterminal thyrses; axis terete, dichotomously branching, 7.5–9 mm long, 0.5–1 mm diam, pubescent; bracts triangular, 0.2–1 by 0.2–0.45 mm, pubescent. Staminate flowers c. 3.2 mm diam; pedicel 4.5–5 mm long, 0.15–0.2 mm diam, gla- brescent; sepals elliptic to lanceolate, 0.8–1.5 by 0.7–1.1 mm, base connate, margin entire, apex rounded to acute, pubescent outside; petals elliptic, 3.4–4.8 by 1.8–2.7 mm, contort, mem- branous, yellow to orange, glabrous; disc annular, c. 0.7–0.8 mm wide, with some irregular notches in margin, fleshy; sta- mens 3, androphore c. 1.5 mm long, c. 0.3 mm diam, anthers ellipsoid, 0.5–0.6 mm long. Pistillate flowers and fruits not seen.

Distribution — India (Assam, endemic).

Habitat & Ecology — In forests. Elevation: 1200–1850 m. Flowering: April to May.

Notes — 1. Within the genus this species grows at perhaps the highest elevation.

2. The new species also resembles T. inopinatus from Australia in the short and dichotomously branching staminate inflorescences, but differs in having a distinctively triplinerved venation.

Figures

Map 6 Distribution of Trigonostemon eberhardtii Gagnep. (★), T. montanus R.Y.Yu & Welzen (▲), T. praetervisus Airy Shaw (■) and T. quocensis Gagnep. (X).

Fig. 3 Trigonostemon montanus R.Y.Yu & Welzen. a. Growing habit; b. leaf base, showing adaxial glands; c. leaf base, adaxial glands fallen; d. staminate inflorescence; e. staminate flower; f. staminate flower, petals and 2 sepals removed, showing the androphore and disc (all: Koelz 27903, barcode L.2260526). — Drawing by Esmée Winkel, 2019.