Trigonostemon sandakanensis Jabl.

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 209

25. Trigonostemon sandakanensis Jabl. — Fig. 13 ; Map 8

Trigonostemon sandakanensis Jabl.(1963) 159,f. 5, 6; Airy Shaw (1975) 204; R.I. Milne (1995a) 27, in key, 30, in key. — Type: SAN (Wood) 16018 (holo SING;iso BO,BRI*, K, KEP ,L, SAN, SING ),British North Borneo [Sabah], Kabili-Sepilok Forest Reserve, 15 miles W of Sandakan, Compartment 10.

Small trees, up to 5 m tall; barely branching, main branch occasionally with adventitious roots; flowering branches c. 1.2 cm diam. Outer bark dark brownish, slightly wrinkled; inner bark brown, sap red; sapwood pale yellowish; heartwood white. Stipules not seen, caducous, scars 0.5–0.6 mm diam. Leaves clustered at the end of branchlets; petiole less than 1 cm long, often lignified and somewhat sheathing; blade oblanceolate, large, 35–45 by 9–13 cm, coriaceous, base cuneate, evenly narrowing into the petiole, margin distantly serrate, teeth subulate, apex caudate, acuminate, apiculate or notched, dark green above, dull and pale green beneath, both sides sericeous; midrib slightly raised on both sides, robust, pubescent and velutinous, nerves 30–40 pairs, curved and more or less connected near margin, veins scalariform, veinlets reticulate, often obscure. Inflorescences: staminate ones subterminal, thyrsoid, short cymes on each node, main rachis erect, up to 20 cm long, sericeous; bracts linear or narrowed lanceolate, up to 7.5 by 1 mm, apex acuminate, abaxially sericeous; pistillate inflorescences racemose, almost spike-like when young, c. 5 cm long when flowering, up to 20 cm long when fruiting, densely sericeous. Staminate flowers 6–10 mm diam; pedicel 5–8 mm long, c. 0.2 mm diam, slightly hairy; sepals elliptic, 2–3 by 1.5–2 mm, apex rounded, reddish, glabrous on both sides; petals linear, 8–9 by 1.2–1.6 mm, margin often reflexed, apex acute, pinkish or pale purplish, outside smooth, inside rough, somewhat papillate and with numerous small and short, generally longitudinal ridges; disc annular, c. 1.6 mm diam, c. 0.4 mm wide, fence-like because of c. 20, apically undulate lobes; stamens 5, androphore erect, 0.6–1 mm long, pubescent at base, anthers clustered at top of androphore, ellipsoid, c. 0.7 mm long, thecae orange and connectives blackish when dry, thickened, protruding and often with few expanded cells apically. Pistillate flowers of same size as staminate ones; pedicel c. 7 mm long, apically c. 0.8 mm diam, elongating in fruit to up to 4 cm long, apically c. 1.5 mm diam, densely sericeous; sepals, petals and disc as staminate flowers; ovary c. 1 mm diam, densely sericeous, style c. 0.2 mm long, stigmas c. 0.7 mm long, bifid into 2 slightly thickened arms, each arm c. 0.5 mm long. Fruits c. 1 cm diam, hirsute, sepals persistent but not accrescent; wall c. 0.7 mm thick, exocarp partly detaching; columella 5–6.5 mm long. Seeds 7–7.5 mm diam; hilum rhombic, 3–4 by 2.5–3.5 mm.

Distribution — Borneo (Sabah, endemic).

Habitat & Ecology — Primary forest, near stream. Altitude: 5– 20 m. Flowering: April to June; fruiting: December.

Note — A unique species only known from the Kabili-Sepilok Forest Reserve in Sandakan, Sabah. The petals are linear and the inner surface is very rough and scurfy.

Figures

Fig. 13 Trigonostemon sandakanensis Jabl., from Kabili-Sepilok Forest Reserve, Sandakan, Sabah, Malaysia. a. Growing habit; b. adventitious root on the main branch; c. red exude. — Photos by Ren-Yong Yu.