Trigonostemon pentandrus Pax & K.Hoffm.

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 204-206

21. Trigonostemon pentandrus Pax & K.Hoffm. — Fig. 9 , 10 ; Map 8

Trigonostemon pentandrus Pax & K.Hoffm. (1914) 406; Jabl. (1963) 164. — Type: Hubert Winkler 1792 (not traced),Malaya,Gunung Angsi near Sungei Gadub. Neotype (designated here): KEP FRI (R. Y. Yu) 86653 (holo L; iso KEP ), Malaysia, Negeri Sembilan, Gunung Angsi.

Small trees, 1–2.5 m tall; flowering branches 5–7 mm diam, pith sometimes of loose tissue. Outer bark 0.2–0.25 mm thick, pale greyish, slightly fissured, glabrous; inner bark 0.15–0.4 mm thick, dark reddish to brownish, fibrous, sap orange; wood 0.5–0.6 mm diam, whitish to yellowish. Stipules subulate to nipple-like, 0.5–1 mm long, glabrous. Leaves: petiole terete, 3.5–8 cm long, 2–3.2 mm diam, glabrous, thickened at base and apex, base somewhat sheathing; blade oblong, 23–35 by 6–9.5 cm, coriaceous, base cuneate, with 2 adaxial glands, nipple-like, showy, margin distantly serrate, teeth short-subulate, thickened, apex acuminate to caudate, upper side dark green, lower side pale green, both sides glabrous; venation penninerved, glabrous, midrib robust, slightly raised above and distinctly elevated beneath, nerves 14–16 pairs, straight, narrowed and branched and connected along margin, veinlets reticulate, often obscure. Inflorescences bisexual, (sub)terminal, short racemose, rigid, staminate flowers at top, pistillate flowers below, 2–6.5 cm long, rachis 1.3–2 mm diam, densely hirsutulous. Staminate flowers 6–7 mm diam; pedicel 2–3 mm long, 0.4–0.5 mm diam, pinkish red, hispidulous; sepals elliptic, 1.3–2 by 1–1.5 mm, white, base connate, margin entire or slightly irregularly undulate, ciliate, apex acute to rounded to emarginate, hirsutulous outside, glabrous inside; petals obovate, 3–4.2 by 2.5–3.2 mm, pink, base narrowed and somewhat claw-like, margin often wrinkled, apex bilobed, glabrous on both sides; disc lobes glandular, 0.6–0.7 by 0.3–0.6 mm, c. 0.15 mm thick, glabrous; stamens 5, androphore erect, 0.7–1 mm long, 0.2–0.3 mm diam near base, slightly narrowed above, 5-cleft at apex; anthers ellipsoid, 0.9–1 mm long, free, divaricate, connectives apically often with numerous dark reddish droplets (expanded cells) with secretion. Pistillate flowers c. 0.3 mm diam (petals fallen); pedicel c. 1.7 mm long, articulated at base, c. 0.5 mm diam when flowering, slightly elongating in fruit to 3.5–4.5 mm long and c. 1.5 mm diam, hirsutulous; sepals elliptic to triangular, 2–2.8 by 1–1.2 mm, margin entire, ciliate, apex rounded to acute to acuminate, hirsutulous outside, glabrous inside; petals not seen, fallen; disc as staminate flowers; ovary c. 1.2 mm diam, reddish, densely hispid; styles indistinct; stigmas deeply fibid into 2 arms of 1.2–1.5 mm length, thickened at apex. Fruits c. 5.5 mm diam, red in living plants, brownish when dry, densely hispid, sepals (slightly accrescent) and stigmas persistent; wall 0.4–0.5 mm thick, exocarp less than 0.1 mm thick, not detaching; columella c. 5 mm long. Seeds not seen.

Distribution — Malay Peninsula (Gunung Angsi, endemic).

Habitat & Ecology — Flowering and fruiting: September to December.

Notes — 1. The species resembles T. verticillatus but a few unusual or unique characters make the species quite distinct: thicker leaves, one pair of showy blackish adaxial glands on leaves (glands not showy, but sometimes can be two pairs in T. verticillatus ), shorter inflorescences and pinkish instead of reddish purple flowers.

2. The species has remained inadequately known and was only mentioned once ( Jablonski 1963) since the original publication. The original type collection (Hubert Winkler 1792) is not seen by us and is presumably lost, but our field observations and collections from Gunung Angsi (type locality) match the original description by Pax & Hoffman (1914) very well. We are strongly convinced that this is a good and distinct species. For more specimen citations, see Identification List.

Figures

Fig. 9 Trigonostemon pentandrus Pax & K.Hoffm. a. Flowering branch; b. staminate flower (3 sepals and petals removed); c. fruits (all: Franck 1372, C). — Drawing by Esmée Winkel, 2016.

Fig. 10 Trigonostemon pentandrus Pax & K.Hoffm., from Gunung Angsi, Negri Sembilan, Malay Peninsula. a. Growing habit; b. bark; c. orange exude; d. leaf base with adaxial glands; e. top view of the tree; f. inflorescences, ants are potential pollinators; g, h. staminate flowers; i, j. fruits. — Photos by Ren-Yong Yu.