Trigonostemon detritiferus R.I.Milne

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 191-192

7. Trigonostemon detritiferus R.I.Milne — Fig. 4 ; Map 4

Trigonostemon detritiferus R.I. Milne (1994) 446, f. 2; (1995a) 27, in key, 28, in key. — Type: Dransfield 6913 (holo K; iso BRUN), Brunei, Teburong District , Selapon.

Small trees, up to 2.5 m tall, 5–12 mm diam, without branches, adventitious roots present at the top of the main branch, 0.2–0.5 mm thick, much branched and curly, dirty and puberulent. Outer bark 0.3–0.4 mm thick, brownish; inner bark 0.5–0.6 mm thick, dark reddish, sap reddish; sapwood c. 1.6 mm thick, yellowish; heartwood c. 2.5 mm diam. Stipules subulate, c. 1.3 by 0.5 mm, pubescent, caducous. Leaves clustered on top of the stem; petiole 0.4–1 cm long, 2–2.5 mm diam, wrinkled and slightly pubescent, upper side flat, lower side rounded; blade oblanceolate, 20–45 by 5.5–10 cm, chartaceous, base rounded to cuneate, adaxial glands not seen, margin distantly serrate, teeth falcate, apex acuminate to almost caudate, upper side glabrous, lower side paler, densely pubescent on especially the venation; venation penninerved, midrib robust, slightly raised on both sides, nerves 15–30 pairs, curved, veins scalariform, veinlets reticulate. Inflorescences: staminate ones flowers single and cauliflorous, axillary, on upper part of branch, or thyrses inserted at leaf axils, 1–7 cm long, few-branched and few-flowered, rachis appressed puberulous; bracts linear to lanceolate, 2–20 by 0.3–6 mm, puberulent; pistillate ones single, inserted at leaf axils. Staminate flowers: pedicel up to 4 mm long; sepals elliptic, 1–1.5 by 0.5–0.8 mm, pubescent outside, glabrous inside; petals obovate, 2–3 by 1–1.8 mm, apex rounded, reddish purple, glabrous; disc glandular, yellowish, c. 0.15 diam; stamens 3, androphore c. 0.5 mm long, anthers pinkish, ellipsoid, 0.4–0.5 mm long. Pistillate flowers: pedicel up to 3.5 cm long, puberulous; sepals and petals as in staminate flowers; disc glands glandular, c. 0.15 mm diam; ovary 0.25–1 mm diam, glabrous to pubescent; styles trifid, indistinct, stigmas slightly to deeply bifid. Fruits c. 6 mm diam, sometimes only one locule mature, other two aborted. Seeds opalescent when young, dark brownish when mature, marbled. Seedling: cotyledons 2, sessile, round, light green, triplinerved. First true leaf subsessile, obovate, base cordate, apex acute, blade light green.

Distribution — Borneo (Temburong District of Brunei, endemic).

Habitat & Ecology — Primary mixed dipterocarp forest, near rivers (c. 30–300 m away from river bank). Flowering and fruiting: June to November.

Notes — 1. The species strongly resembles T. wetriifolius in the growing habit, cauliflorous flowers and adventitious roots, while the distinct differences lie in the dark reddish (vs pale yellowish in T. wetriifolius ) petals and 3 (vs 5 in T. wetriifolius ) stamens.

2. This species has a special living strategy (also seen in T. wetriifolius , see Airy Shaw & Ng 1978).The leaves are always clustered on the top of the main branch, where the adventitious roots also generate, thus the leaves accumulate dirt and fallen leaves from inside and form humus , from which the nutrition can be absorbed by the adventitious roots.

Figures

Fig. 4 Trigonostemon detritiferus R.I.Milne, from Kuala Belalong, Temburong, Brunei. a. Growing habit; b, c. short branch, showing bark and cauliflorous flowers; d. top view of the tree, leaves arranged in whorls and used to trap fallen leaves; e. reddish exude; f. staminate flower; g. pistillate flower; h. fruit; i. seedling with 2 cotyledons; j. true leaves growing from the seedling. — Photos by: a–h: Ren-Yong Yu; i, j: Ferry Slik.