Trigonostemon malaccanus Müll.Arg.

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 201-203

18. Trigonostemon malaccanus Müll.Arg. — Fig. 8 ; Map 7

Trigonostemon malaccanus Müll.Arg. (1864a) 482; (1866) 1110; Hook.f. (1887) 396; Pax & K.Hoffm. (1911) 90; Ridl. (1924) 265; Jabl. (1963) 154; Whitmore (1973) 136; Airy Shaw (1981) 355. — Type: Griffith KD 4782 (holo K), Malaya, Malacca.

Small trees, up to 6 m tall, stem at least up to 5 cm diam; flowering branches up to 7.5 mm thick, glabrous or slightly pubescent in young parts, sometimes hollow. Bark c. 0.3 mm thick, smooth, brownish to greyish to blackish; sap clear or orange; wood pale yellowish. Stipules falcate or subulate, c. 1 mm long, often pubescent near base. Leaves clustered near apex of branches; petiole terete but grooved above, 2.5–22 cm long, sometimes thickened at apex or base, slightly pubescent, glabrescent; blade lanceolate, oblong or occasionally ovate, 10–25(–40) by 3–14 cm, chartaceous to coriaceous, base acute to rounded, with 2 adaxial, subulate or falcate glands, margin distantly serrate, teeth small, falcate or nipple-like, apex acuminate to caudate, glabrous above, sparsely pubescent along venation beneath; midrib elevated and slightly pubescent (glabrescent in large leaves) on lower side, nerves 8–13 pairs, slightly curved and narrowed along margin, veinlets reticulate, often obscure. Inflorescences mainly unisexual, staminate ones thyrsoid, often terminal or subterminal, with short cymes along the main rachis, up to 25 cm long, densely hirsutellous, condensed when young; involucral bracts 2 or more, lanceolate to falcate, up to 2 by c. 0.5 mm; bracteate under cymes and under each flower, bracts lanceolate, up to 2 by 0.9 mm and 0.6 by 0.4 mm, respectively, hirsutulous; pistillate inflorescences racemose or thyrsoid, 1- or few-flowered cyme at each node, sometimes mixed with a few staminate flowers, up to 30 cm long, hirsutulous, condensed when young. Staminate flowers c. 4 mm diam; pedicel 1.5–2 mm long, 3–5 mm diam, hirsutulous; sepals orbicular to obovate, 1–2.1 by 0.6–1.6 mm, apex rounded, puberulent outside and often with a gland in the middle (on young flowers); petals obovate, c. 2.5 by 1.7 mm, pinkish or reddish purple, base cuneate, margin often wrinkled, apex rounded, glabrous on both sides; disc 0.6–1 mm diam, lobes obtrapezoid, c. 0.5 by 0.5 mm, c. 0.1 mm thick, glabrous, fused when young, separate and wrinkled when flowering, apex recurved and flat; stamens 3, androphore erect, c. 0.5 mm high, c. 0.2 mm diam, anthers free, long ellipsoid, c. 0.5 mm long. Pistillate flowers c. 4.5 mm diam; pedicel 1.5–2 mm long, 0.5–0.7 mm diam when flowering, slightly elongating to c. 4 mm long and 1 mm thick in fruit, hirsutulous; sepals and petals as staminate flowers, but petals caducous when fruiting; disc annular, margin irregularly undulate or with notches; ovary c. 1 mm diam, densely pubescent, style absent, stigmas deeply cleft for at least 3/4. Fruits c. 8 mm diam, puberulent, sepals persistent but not accrescent; wall 0.5–0.6 mm thick, exocarp detaching; columella 4.5–6 mm long. Seeds 5.5–6 by 5–5.5 mm; hilum triangular or heart-shaped, 2.5–3 by 2–2.5 mm.

Distribution — Thailand, Malay Peninsula, Sumatra.

Habitat & Ecology — Evergreen forests to recently logged-over forests on hill ridges or in valleys, sometimes near rivers. Altitude: 100–850 m. Flowering: all year round; fruiting: June to August, November to February.

Vernacular name — Malay Peninsula: Putat.

Notes — 1. Trigonostemon malaccanus resembles T. heteranthus but has stubby staminate pedicels (often shorter than 2 mm, wider than 0.3 mm diam) rather than the slim pedicels of T. heteranthus (often longer than 2 mm and c. 0.1 mm diam), and entire pistillate sepals (vs fimbriate in T. heteranthus ).

2. Trigonostemon malaccanus is also similar to T. verticillatus var. verticillatus but differs by having 5 instead of 3 stamens and the young inflorescences with distinct short and stiff hairs.

Figures

Fig. 8 Trigonostemon malaccanus Müll.Arg., from Forest Research Institute Malaysia, Kepong, Malay Peninsula. a. Growing habit; b. leaves; c. pistillate inflorescence; d. leaf base with adaxial glands; e. pistillate flowers, petals fallen. — Photos by Ren-Yong Yu.