Trigonostemon laevigatus Müll.Arg.

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 195-197

13. Trigonostemon laevigatus Müll.Arg. — Fig. 5 ; Map 5

Trigonostemon laevigatus Müll.Arg. (1864b) 538; (1866) 1111; Boerl. (1900) 232,284; Pax & K.Hoffm.(1911) 94; Merr.(1921) 345 (2nd mentioning,first = Microdesmis caseariifolia Planch. ,see Jablonski 1963: 168);Ridl. (1924) 265; Jabl. (1963) 167; Airy Shaw (1972a) 346; Whitmore (1973) 135; Airy Shaw (1975) 203; (1978) 417; (1981) 355; (1983b) 47; Chantar. (2005) 25; (2007) 578, f. 93. — Lectotype (designated here): Motley 686 (holo K), Borneo, Bangarmassing. Syntype: Barter s. n. (K, barcodes K000959289, K000959290), Borneo.

Trigonostemon everettii Merr. (1912) 408; Pax & K.Hoffm. (1914) 408; Merr. (1923) 451; Airy Shaw (1983b) 46. — Type: FB ( Everett ) 7257 (holo PNH†; iso A), Philippines, Negros , Mt Silay.

Trigonostemon anomalus Merr. (1920) 569; (1923) 451. — Type: FB (Villamil) 22018 (holo PNH †; iso A, US), Philippines, Mindanao, Zamboanga District, Naganaga .

Trigonostemon laevigatus Müll.Arg. var. petiolaris Airy Shaw (1978) 417; R. I. Milne (1995a) 28, in key, 29, in key. — Type : S (Chai) 19224 (holo K; iso L, SAN, SING ), Sarawak, Fourth Division , Simpang Tiga , Ulu Mayeng, Kakus .

Trigonostemon sp. nov., aff. chinensis Merr.: Jabl. (1963) 168. — Voucher: KEP (Strugnell) 20275 (K, KEP, SING ), Malaya, Pahang, Ulu Gali Raub. See note.

Trigonostemon sp. nov., aff. chinensis Merr.: Jabl. (1963) 168. — Voucher: van Steenis 910 (BO,L, SING), Sumatra,Anambas Islands,Siantan Island, E of Terimpa. See note.

Trees, 5–15 m tall, stem up to 15 cm diam; flowering branches 1.5–2 mm diam, often slightly pubescent near nodes and apical buds. Bark 0.3–0.5 mm thick, smooth, lenticellate, light greenish to pale or dark brownish to blackish; sap red, pink or colourless; wood whitish to reddish brown, with brownish pink rays. Stipules falcate to nipple-like, 0.3–1 mm long, pubescent, caducous, often obscure or not seen. Leaves: petiole terete but often flat or grooved above, 0.5–1.5(–4) cm long, wrinkled, glabrescent to pubescent, base and apex sometimes pulvinate; blade elliptic, sometimes oblong, ovate or oblanceolate, 6 – 20 by 2.5–8 cm, chartaceous or coriaceous, base acute to cuneate, with 2 adaxial glands, margin entire, apex acuminate to caudate, above greenish, underneath pale green below, both sides glabrous; venation triplinerved, midrib elevated beneath, nerves 6–9 pairs, bow-shaped, narrowed along margin, veinlets reticulate, obscure. Inflorescences terminal or axillary, cymes or paniculate thyrses, abbreviated and condensed or elongated and lax, 0.5–4 cm long, often branched, glabrescent or pubescent, bracts long-triangular to linear, up to 3 by 1 mm, velutinous. Staminate flowers 6–10 mm diam; pedicel c. 1 cm long, c. 0.2 mm thick, scarcely pubescent; sepals oblong to obovate to orbicular, 2–4.5 by 1.8–2.5 mm, sometimes unequal, then outer 2 or 3 larger, imbricate, margin entire, apex rounded, yellowish green, often finely puberulent on both sides, outside also pubescent with longer hairs and sometimes with a subapical gland ( var. croceus ); petals flabellate and bilobed, each lobe 3–6 by 1.5–3 mm, yellow or reddish, glabrous, few parallel veins visible, base claw-like, apex notched to 1/3 to 1/2 of length and often with a small gland below the notch; disc annular, c. 0.5 mm high, glabrous, apex recurved; stamens 3, androphore 0.3–1.5 mm high, trifid at apex, filaments 0.2–0.5 mm long, anthers oblong, c. 0.8 mm long, yellow, free, base somewhat auriculate, not divaricate at apex. Pistillate flowers c. 6 mm diam, pedicel thickened towards apex, up to 2.5 cm long, apically c. 1 mm thick, slightly pubescent; sepals, petals and disc as in staminate flowers; ovary c. 1 mm diam, greenish, glabrescent to densely hairy, style c. 0.1 mm long, sometimes indistinct, stigmas 3 separate arms, c. 0.6 mm long, c. 0.1 mm thick, apex very slightly thickened and bifid. Fruits c. 1 cm diam, greenish, finely hairy; wall 0.4–0.6 mm thick, exocarp detaching; columella 5–6.5 mm long. Seeds 7–8 by 6–7 mm; hilum 1.5–3 by 1–2 mm.

Distribution — Vietnam, Thailand, Malay Peninsula, Sumatra, Java, Borneo, Philippines, Lesser Sunda Islands.

Map 5 Distribution of Trigonostemon laevigatus Müll.Arg.var. laevigatus (●) and T. laevigatus var. croceus (B.C.Stone) R.Y.Yu & Welzen (★).

Note — The species is wide-spread and is often recognized by its short petiole, hairy sepals, and often flabellate and bilobed petals. The last three synonyms are only tentatively treated here because of the inadequate material.

Key to the varieties

Figures

Fig. 5 Trigonostemon laevigatus Müll.Arg. var. laevigatus, from Kabili-Sepilok Forest Reserve, Sandakan, Sabah, Malaysia (a–e, g–h), and Kuala Belalong, Temburong, Brunei (f). a. Growing habit; b. leaves; c. reddish exude; d. bark and wood; e. staminate flower; f. pistillate flower; g. pistillate flower, petals fallen; h. fruit. — Photos by Ren-Yong Yu.