Trigonostemon lychnos (R.I.Milne) R.Y.Yu & Welzen, 2018

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

16. Trigonostemon lychnos (R.I.Milne) R.Y.Yu & Welzen , comb. nov. & stat. nov. — Map 7

Trigonostemon polyanthu s Merr. var. lychnos R.I. Milne (1995a) 28, in key,30, in key, 35,f. 2. — Type: Coode 6766 (holo K; iso BRUN, K, KEP , L), Brunei, Tutong District, near Sungai Liang,Andalau Forest Reserve.

Slender treelets, up to 4 m tall, few branched; flowering branches c. 6 mm diam. Bark pale brownish, slightly pubescent near young parts, smooth when mature; sap red; wood reddish brown, pith loose. Stipules falcate, c. 1 mm long, caducous, pubescent. Leaves: petiole variable, 1–22 cm long (on a single flowering branch), terete, slightly grooved above, slightly pubescent when young, glabrous when mature; blade elliptic, 11–33 by 5.5–23.5 cm, chartaceous to coriaceous, base acute, with 2 adaxial glands, margin distantly serrate, teeth small, glandular, apex acuminate, upper side dark green (when dry), glabrous, lower side brownish (when dry), sparsely pubescent (more hairy on venations), more or less ciliate along margin; midrib slightly raised beneath, nerves 9–10 pairs, small veins reticulate. Inflorescences: staminate ones paintbrush-like, peduncle up to 13.5 cm long, bracts lanceolate, 1–1.6 by 0.5–0.7 cm; pistillate ones paintbrush-like but condensed into glomerules, pendulous; peduncles 20–29 cm long, 1.5–3.4 mm diam, terete, glabrous, base with 2 involucral bracts, as stipules, apex with few bracts subtending the glomerule, apical bracts obovate to lanceolate, 3–8 by 1.8–4.2 cm, base acute to reniform, apex acuminate, green, glabrous on both sides, glabrous or sometimes very sparsely pubescent near base; glomerules (few clustered short cymes) glabrous, with few small bracts under each flower, small bracts amorphous, slightly pubescent. Staminate flowers c. 4.5 mm diam, pedicel 4–7 mm long, very thin; sepals elliptic, c. 1.5 by 1 mm, pale pinkish green; petals long elliptic, c. 3 by 1.2 mm, purple; stamens 3, androphore c. 0.5 mm long, anthers with apically droplets on connective. Pistillate flowers unopen, pedicel covered by bracts, unseen; sepals elliptic, c. 3 by 2 mm; petals purple, elliptic, ovary unknown. Fruits and seeds unknown.

Distribution — Borneo (Belait and Tutong districts of Brunei, endemic).

Habitat & Ecology — Mixed lowland forest; heath forest on sandy soil ( Milne 1995a). Altitude: 50 m. Flowering: April.

Vernacular — Sagubang Kayu ( Brunei).

Note — A distinct species with only a few collections. We regard it as a separate species because of its big difference from T. polyanthus in the variable petiole and blade and the showy subtending bracts under the inflorescences. The variable petiole and leaf-like bracts also resemble T. villosus var. merrillianus .