Trigonostemon diplopetalus Thwaites

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 30-31

7. Trigonostemon diplopetalus Thwaites — sect. Pycnanthera — Map 5

Trigonostemon diplopetalus Thwaites (1861) 277; Müll.Arg. (1866) 1108; Hook.f., (1887) 398; Trimen (1898) 51, pl. 83; Pax & K.Hoffm. (1911) 93, f. 39;N.P.Balakr.& Chakrab.(1991) 613,f. 3; Philcox (1997) 110. — Lectotype (designated here): Thwaites CP 578 (G*, barcode G00435106; iso A,barcode A00048867,BR*,barcode BR0000005105045,CAL, barcodes CAL0000023676,CAL0000023677,FR*, barcode FR0036073,G*, no barcode, in the same folder with lectotype; G-DC*, barcode G00319791, on 2 sheets, GH*, barcode GH00048868, K, barcode K000246865, P, barcodes P00717097, P00717098), Sri Lanka.

Shrubs or small trees; flowering branches 2–2.8 mm thick, pubescent when young, glabrous in older parts. Outer bark 0.1– 0.2 mm diam, dark to pale brown; inner bark 0.1–0.3 mm thick; wood pale yellow. Stipules subulate, 0.4–1 mm long, caducous, pubescent at base. Leaves: petiole terete but grooved above, 0.5–1.2 cm long, 1–1.7 mm diam, slightly pubescent when young; blade oblong to oblanceolate, 14–23.5 by 3.5–5.5 cm, thick chartaceous, lower part cuneately narrowed, decurrent into petiole, 2 adaxial glands present, falcate, margin distantly serrate, teeth falcate, apex acuminate, both surfaces glabrous, slightly pubescent beneath when young; venation pinnate, mid- rib almost flat above, elevated beneath, secondary veins 11–16 pairs, bifurcate and connected along margin, tertiary veins reticulate, obscure. Inflorescences bisexual, racemose thyrses, terminal; axis 3.3–17 cm long, 1.2–1.7 mm diam, pubescent; bracts lanceolate, 0.2–1.3 by 0.4–0.7 mm, pubescent. Staminate flowers (bud) 2–2.2 mm diam; pedicel 1.1–2.5 mm long, 0.35–0.4 mm diam, pubescent; sepals lanceolate, 1.3–1.5 by 0.5–0.7 mm, base connate, apex rounded to acute, pubescent outside; petals ( Trimen 1898) about as long as sepals, denticu- late and crisped, bilobed, red; disc glands 5 ( Balakrishnan & Chakrabarty 1991), c. 0.2 by 0.3 mm; stamens ( Balakrishnan & Chakrabarty 1991) 3, sessile? (see note 2), connective fleshy, forming a stalk, c. 0.5 mm long. Pistillate flowers (bud) 2–2.1 mm diam; pedicel 5.2–6 mm long, apically 0.5–0.7 mm diam, pubescent; sepals lanceolate to oblong, 2–2.6 by 0.7–1 mm, apex acuminate, pubescent and gibbose (with a horn-like ap- pendage) outside ( Balakrishnan & Chakrabarty 1991); petals ( Trimen 1898) as in staminate flowers, but larger and reflexed; ovary ( Philcox 1997) pubescent, stigmas ( Trimen 1898) apically twice bifid, with short stout branches. Fruits ( Philcox 1997) 1–1.5 cm diam, subglobose. Seeds ( Philcox 1997) 5.5–6 mm diam, pale brown, with shallow longitudinal ridge.

Distribution — Sri Lanka (endemic).

Habitat & Ecology ( Trimen 1898) — Forests in moist regions. Elevation: 0– 300 m. Flowering: March to May, September.

Notes — 1. A very rare species, endemic to Sri Lanka. It is possibly allied to T. nemoralis Thwaites because of the sessile anthers. The petals are bilobed.

2. In Balakrishnan & Chakrabarty’s revision (1991), the anthers are said to be sessile in the text, but the illustration shows a filament below, supporting the anthers.