Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl.

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 187

2. Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl. — Fig. 1 ; Map 2

Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl. (1900) 284; Pax & K.Hoffm. (1911) 93; (1931) 170; Jabl. (1963) 164, in obs.; Airy Shaw (1969) 126; (1972a) 345, f. 11; Whitmore (1973) 136; Airy Shaw (1974) t. 3721; (1981) 352;Chantar.(2007) 576. — Tylosepalum aurantiacum Kurz ex Teijsm. & Binn. (1864) 50. — Codiaeum aurantiacum (Kurz ex Teijsm. & Binn.) Müll.Arg. (1866) 1118. — Lectotype (designated here): Teijsmann s. n. (L, barcode L.2260196), Indonesia, Java, cultivated in Bogor Botanical Garden (originally from Bangka?). Actephila aurantiaca Ridl. (1923) 360;(1924) 197. — Type: Ridley s. n., Feb. 1917 (holo K, barcode K000959323), Malaya, Kelantan, Chaning Woods. Actephilopsis malayana Ridl. (1923) 361; (1924) 252;M.R.Hend. (1939) 68. — Trigonostemon malayanus (Ridl.) Airy Shaw (1967) 413. — Syntypes: Curtis 674 (K),Malaya,Penang,Ayer Hitam; Haniff 1611 (?), Malaya,Perak, Gunung Kerbau; Ridley 2300 (K), Malaya, Pahang, Kwala Tembeling.

Shrubs or small trees, 1.5–3(–6) m tall, stem up to 10 cm diam; flowering branches up to 2 mm thick, smooth, brownish. Bark c. 2 mm diam; sap red and sticky; wood pale brown. Stipules subulate, c. 1.5 mm long, hirsute. Leaves: petiole 0.5–3 cm long (depending on leaf size), slightly wrinkled and grooved above, more or less pubescent; blade elliptic to oblong, 8–30 by 2.5–12 cm, chartaceous to coriaceous, base acute, with 2 glands adaxially, occasionally developing into stipellae, margin distantly serrate, teeth falcate or subulate, apex acuminate, young blade reddish, mature ones dark green above, light green beneath, glabrous or scattered pubescent on lower side; venation penninerved, midrib slightly raised above, distinctly elevated beneath, nerves 8–13 pairs, straight, branched and connected near margin, small veins reticulate, often obscure. Inflorescences: staminate ones cauline, few short and condensed thyrses, often bracteolate and with 1 flower per node; pistillate ones terminal or axillary, often racemose or paniculate, sometimes mixed with a few staminate flowers; bracteate under each branch and flower, the main rachis (and sometime secondary rachises) often subtended by large, leaf-like bracts, shortly (up to 5 mm) petiolate, blade elliptic or ovate, up to 7 by 3.5 cm, base often cordate, apex acuminate. Staminate flowers c. 6 mm diam; pedicel very slender, up to 1 cm long, c. 0.1 mm diam, pinkish, glabrous; sepals unequal, oblong, 1.2–1.5 by 0.5–1 mm, imbricate, yellowish or reddish, connate at base, apex rounded, more or less pubescent outside, with an often showy gland in the middle outside; petals oblong, c. 4 by 1.3 mm, orange, with a reddish honey mark at base, visible on both sides, inside often paler and outside sometimes with whitish margin, few parallel veins often visible, apex acute, glabrous on both sides; disc glands more or less trapezoid, thick and fleshy, c. 0.2 by 0.5 mm, c. 0.2 mm thick, apex flat; stamens 3, androphore erect, c. 0.5 mm long, trifid at top, anthers free, divaricate, each theca c. 0.6 by 0.2 mm. Pistillate flowers c. 5.5 mm diam, pedicel thickening towards apex, up to c. 7 mm long, apically c. 0.7 mm diam when flowering, up to c. 2 cm long and apically c. 1 mm diam when fruiting, glabrous; sepals as in staminate flowers, persistent in fruits; petals obovate, c. 3.5 by 2 mm, orange outside and paler inside, base cuneate or somewhat claw-like, with a reddish (dark reddish pigment granules in epidermis cells visible) honey mark, apex often rounded; disc lobes broad, almost rectangular, truncate at apex, c. 0.3 by 0.7 mm, thin, membranous; ovary c. 1.1 mm diam, glabrous, light yellowish; styles short, c. 0.2 mm long, stigmas 3, light yellowish, slightly thickened, apically split and somewhat horseshoe-shaped. Fruits c. 1.2 cm diam, greenish to reddish, glabrous; sepals not accrescent; wall c. 1 mm thick; columella c. 5.5 mm long. Seeds c. 5.5 mm diam, dark orange when dry, hilum somewhat heart-shaped or rhombic, c. 1.5 mm diam.

Distribution — Thailand, Malay Peninsula, Sumatra, Java, Bali.

Habitat & Ecology — Lowland evergreen (often dipterocarp) forests, growing in understorey on limestone, along streams or on hill slopes. Altitude: 0– 600 m. Flowering and fruiting: all year round.

Notes — 1. A species variable in shape and size of the leaves. It shows similarities with T. wildeorum , from which it can easily be differentiated by its racemose or paniculate pistillate inflorescences (vs pistillate flowers always inserted in leaf axils and the pistillate sepals always strongly accrescent in T. wildeorum ).

2. One specimen (P. E. Schmutz 524, Lesser Sunda Islands, Flores) with elliptic and dark brownish to greyish leaves and a short (c. 1.5 cm) staminate peduncle, seems to be an intermediate form between T. aurantiacus and T. hartleyi (endemic to New Guinea), and even the location of the collection is between W Malesia and New Guinea. Since no other specimens are known and T. hartleyi is a poorly understood species, this specimen cannot be accurately identified and the Lesser Sunda Islands is here not included in the distribution of T. aurantiacus .

Figures

Map 2 Distribution of Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl.

Fig. 1 Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl., cultivated in Bogor Botanical Garden (XV.J.A.XXXI.15, originally from Indo-China), Java, Indonesia. a. Growing habit; b. leaves; c. short branch with cauliflorous flowers; d. staminate flowers; e. fruit. — Photos by Ren-Yong Yu.