Trigonostemon calcicolus (R.I.Milne) 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 : 189-190

5. Trigonostemon calcicolus (R.I.Milne) R.Y.Yu & Welzen , comb. nov. & stat. nov. — Map 3

Trigonostemon polyanthu s Merr. var. calcicolus R.I. Milne (1995a) 28, in key, 30, in key, 33, f. 1. — Type: Chew Wee -Lek 679 (holo K; iso L), Sarawak, 1st Division , Kuching District , Tiang Bekap, Mt Mentawa, N1°12' E110°23' .

Small trees, 3 m tall; flowering branches c. 3 mm diam. Outer bark c. 0.1 mm thick, brownish, pubescent to hirsutellous when young, hairs short and stiff; inner bark c. 0.1 mm thick, dark reddish; wood pale brown to reddish brown. Stipules subulate, c. 0.7 mm long, caducous, hirsutellous. Leaves: petiole 4.6–9 cm long, terete but grooved above, hirsutellous; blade broadly elliptic, 16–23.5 by 7–11.5 cm, base acute to rounded, adaxially 2 glands present but caducous, margin entire or slightly distantly serrate, ciliate, apex acuminate to rounded, upper side dark brown to black (when dry), glabrous, lower side brown (when dry), scarcely pubescent to hirsutellous; midrib slightly raised and glabrous above, distinctly elevated and hirsutellous beneath, nerves 9–13 pairs, slightly raised and hirsutellous beneath, small nerves reticulate, obscure. Inflorescences axillary, unisexual; staminate ones thyrsoid, flowers clustered into few very short cymes (nearly a glomerule) at apex of rachis, rachis 2.5–5 cm long, 0.6–0.9 mm diam, hirsutellous; bracts to glomerules elliptic to lanceolate, 7–15 by 1.5–5 mm, apex acute to acuminate, hirsutellous outside, bracts to the flowers small, triangular to lanceolate, c. 0.3 by 0.1 mm, hirsutellous outside; pistillate inflorescences similar to staminate ones but with fewer flowers, 7–10 cm long, 0.7–1.1 mm diam, hirsutellous; bracts to the flowers lanceolate, c. 5 by 1.5 mm, hirsutellous outside. Staminate flowers (unopened) 1.1–1.6 mm diam; pedicel 0.5–2 mm long, 0.3–0.5 mm diam (apex), thickened towards apex, densely hirsutellous; sepals elliptic, 0.5–1 by 0.3–0.5 mm, apex acute to rounded, hirsutellous outside; petals orbicular to elliptic, 0.5–0.6 mm diam, black, glabrous on both sides; disc indiscernible; stamens 5, androphore indiscernible, anthers ellipsoid, c. 0.4 mm long, connectives with apically some droplets (expanded cells) with secretion. Pistillate flowers: sepals triangular, c. 3 by 1 mm, green, thin, pubescent outside; petals elliptic-ovate, c. 1.2 by 1 mm, black, glabrous; disc insignificant; ovary strongly pyriform, c. 0.8 mm diam, glabrous, yellow; stigma slightly divided. Fruits ( Milne 1995a): oblong-ovate, c. 9 by 8 mm; pedicel c. 10 mm long, pubescent; sepals persistent, puberulous, drying brownish grey. Seeds unknown.

Distribution — Borneo ( Sarawak, endemic).

Habitat & Ecology — On limestone. Altitude: recorded once from 80 m. Flowering: July.

Note — The descriptions of the pistillate flowers and fruits are based on Milne (1995a). This species is only known from the type collection from Sarawak. The species has the same characteristics of T. villosus var. merrillianus (e.g., long petiole, glomerules on inflorescences), but has 5 instead of 3 stamens. Since the number of stamens is generally reliably constant per species, this taxon is here regarded as a distinct species rather than a variety as it is in Milne (1995a).