Trigonostemon rufescens Jabl.

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 209

24. Trigonostemon rufescens Jabl. — Fig. 12 ; Map 8

Trigonostemon rufescens Jabl. (1963) 152, f. 2; Whitmore (1973) 135. — Type: SFN (Corner) 29428 (holo SING; iso A*, BO, K, L, SAN, SING ), Malaysia, Johore, 13.5 miles on Mawai – Jemaluang Road .

Small trees, up to 3 m tall; flowering branches 4–6 mm diam. Indumentum of densely golden hispid hairs. Outer bark c. 0.1 mm thick, dark brownish, hispid; inner bark c. 0.1 mm thick, blackish, sap red; sapwood 0.85–1 mm thick, whitish to pale yellowish; heartwood 2.6–2.8 mm diam, pale brownish, often hollow. Stipules subulate, c. 1 mm long, densely hispid, caducous. Leaves: petiole subterete, more or less furrowed above, 2–13 cm long, hispid; blade oblong to oblanceolate, 18–32 by 5–12 cm, coriaceous, base cuneate, acute to rounded or narrowly cordate, 2 adaxial glands often present, margin very distantly serrate, teeth subulate, apex acuminate to aristate, densely golden hispid on both sides; midrib flat above and elevated beneath, with two layers of hairs, soft pilose and hispid, nerves 11–14 pairs, curved and narrowed near margin, veins reticulate, often obscure above and distinct beneath. Inflorescences: staminate ones racemes or glomerules, 2 –9 cm long, hispid; bracts lanceolate or linear, 8–20 by 1–5 mm, hispid; pistillate inflorescences racemose, up to 6 cm long, axillary, few-flowered (often only the top one develops), hispid; bracts as staminate ones. Staminate flowers c. 6 mm diam; pedicel at least 3.5 mm long, c. 0.4 mm diam, sparsely hirsutulous; sepals oblong, at least 3 by 1.2 mm, villose outside, glabrous inside; petals obovate or oblong, 3.5–5.5 by 1.5–2.2 mm, dark reddish, both sides glabrous; disc lobes elliptic, c. 0.4 by 0.4 mm, apex acute, glabrous; stamens 5, androphore erect, c. 1.5 mm long, 5-cleft at top, filament 0.3–0.4 mm long, anthers free, divaricate at top into two lobes, each lobe 0.65–0.8 mm long. Pistillate flowers c. 1.2 cm diam; pedicel c. 6.5 mm long, c. 0.7 mm diam, hispid; sepals lanceolate, 5.5–6.6 by 1.5–2.5 mm, apex acuminate, densely hispid outside, sparsely hispid inside; petals elliptic, c. 4.5 by 2 mm, margin wrinkled and irregular, apex near acute, glabrous on both sides; disc lobes rectangular to semi-orbicular, c. 0.4 by 0.8 mm, glabrous; ovary c. 1.3 mm diam, glabrous, evenly narrowed at top, styles c. 0.3 mm long, stigmas c. 1 mm long, bifid to middle. Fruits (immature) c. 7 mm diam, pinkish, pedicel c. 1 cm long, c. 2 mm diam (top); persistent sepals triangular, 1.2–1.5 by 0.6 mm. Seeds not seen.

Distribution — Malay Peninsula (Mawai – Jemaluang Road, endemic).

Habitat & Ecology — In drier part of swamps and on dry hill rocks. Flowering: February, May.

Notes — 1. This is a densely hairy species but the ovary turns out to be completely glabrous in our dissection, which is different from Jablonski’s (1963) original description.

2. It is only known from its type locality where most of the forests have been replaced by oil palm plantations and the species, resampled in 2016 by the first author, is now extremely threatened.

Figures

Fig. 12 Trigonostemon rufescens Jabl., from Mawai, Johor, Malay Peninsula. a. Growing habit; b. top view of a branch; c. leaf base with a hispid petiole and two adaxial glands; d. bark; e. red exude; f. staminate flower; g. fruit. — Photos by Ren-Yong Yu.