Trigonostemon wildeorum 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 : 222-224

34. Trigonostemon wildeorum R.Y.Yu & Welzen , sp. nov. — Fig. 20 ; Map 10

This species resembles T. aurantiacus , but differs in the flowers with the sepals covered by dense silky hairs and in the 5 (in stead of 3) stamens. — Type: W. J. J. O de Wilde & B. E. E. de Wilde - Duyfjes 20274 (holo L; iso BO), Indonesia, North Sumatra, Atjeh, Middle Alas River (Lae Sauraya) area , c. 15 km N of Gelombang , S of Bengkong River , N2°55' E99°57'. Paratype : W. J. J. O de Wilde & B. E. E de Wilde -Duyfjes 18742 ( BO, KLU, L, P), Indonesia, North Sumatra, Atjeh, southern part of the reserves, Alas River valley , near the mouth of the Bengkong River , c. 50 km S. of Kutacane , N3° E97°50' .

Small trees, 2–4.5 m tall; flowering branches 1.5–3 mm diam, buds golden sericeous. Bark c. 0.3 mm thick, pale greyish, appressed sericeous to hirsutulous when young, often smooth and fissured when mature; sapwood c. 2 mm thick, brownish; heartwood c. 2 mm diam, whitish. Stipules subulate, 0.5–0.6 mm long. Leaves: petiole terete, 0.5–1 cm long, flat above, rounded beneath, appressed hirsutulous; blade obovate, 7.5–22 by 3.5–7.5 cm, chartaceous to coriaceous, base cuneate to acute, 2 adaxial glands present, these subulate to falcate, caducous, margin entire to distantly serrate, ciliate, teeth small and falcate, apex caudate, tip 0.8–2.5 cm long, sometimes slightly slanting, upper side dark brownish (when dry), sparsely sericeous when young, pale brownish to greyish (when dry), glabrescent when mature, lower side brownish, sparsely sericeous; venation penninerved, midrib flat above and elevated beneath, hirsutulous to sericeous on both sides, nerves 8–12 pairs, straight, branched and slightly curved along margin, often hirsutulous beneath, veinlets reticulate. Inflorescences reduced to a cauliflorous fascicle of at most 3 flowers; bracts oblong to linear, 1–2.5 by 0.3–0.5 mm, hirsutulous. Staminate flowers c. 6 mm diam; pedicel c. 0.5 mm long, 0.3–0.4 mm diam, densely hirsutulous; sepals elliptic, 1.5–2 by 0.8–1.3 mm, base connate, margin entire, apex acute to rounded, outside densely sericeous to hirsutulous, inside slightly floccose; petals obovate, c. 3.5 by 2.5 mm, dark purplish black, base slightly claw-like, entire, apex rounded, glabrous on both sides, few dark palmate veins often visible; disc lobes semi-orbicular, 0.4–0.5 by 0.6–0.8 mm, apex sometimes with a shallow notch; stamens 5, monadelphous, androphore erect, c. 1 cm long, c. 0.3 mm diam, anthers free, ellipsoid, divaricate, each theca c. 0.5 by 0.3 mm. Pistillate flowers c. 5 mm diam (not fully opened); pedicel c. 1 mm long, apically c. 1 mm diam, slightly thickened near apex, densely pubescent; sepals triangular, 3–3.5 by 1.5–2.5 mm, base narrowed and connate, margin serrate, apex acuminate, outside densely hirsutulous to sericeous, inside hirsutulous to pubescent, accrescent in fruits, then elliptic to ovate, up to 1.3 by 1 cm, base rounded to truncate, margin distantly serrate, apex acute, sometimes with a small notch, outside a few palmate veins visible, sericeous especially on veins, inside sparsely sericeous; petals ovate to elliptic, c. 2.5 by 1.5–2 mm, dark purplish black, caducous, margin entire, apex acute to acuminate, glabrous; disc lobes as staminate flowers; ovary c. 0.8 mm diam, densely pubescent, style indistinct, stigmas c. 0.9 mm long, deeply bifid, arms c. 0.7 mm long, thickened and slightly sagittate at base. Fruits c. 1 cm diam, puberulent outside; wall c. 0.5 mm thick, exocarp partly splitting off; columella c. 5 mm long. Seeds c. 6 mm diam.

Distribution — Sumatra (endemic).

Habitat & Ecology — Primary foothill forest on yellow-red loamy soil over basalt rock. Altitude: 50– 200 m. Flowering and fruiting: July.

Note — Only known from the two collections mentioned above.

Figures

Fig. 20 Trigonostemon wildeorum R.Y.Yu & Welzen. a. Flowering branch; b. staminate flower, showing the sepals and petals (one sepal removed);c. pistillate flower, showing the accrescent sepals; d. staminate flower (sepals and petals removed); e. pistillate flower; f. one dehiscing coccus with a marbled seed (all: W.J.J.O de Wilde & B.E.E. de Wilde-Duyfjes 20274, L). — Drawing by Esmée Winkel, 2016.