Trigonostemon serratus Blume

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 212

27. Trigonostemon serratus Blume — Map 10

Trigonostemon serratus Blume (1825) 600 ( ‘ serratum ’); Müll.Arg. (1866) 1110; Pax & K.Hoffm. (1911) 92; Backer & Bakh.f. (1963) 495; Airy Shaw (1982) 36. — Lectotype (designated here): Blume 1648 (L, barcode L.2258717; isolecto L, barcodes L.2258713, L.2258714, L.2258716), Java, Nusa Kambanga.

Small trees; flowering branches terete, 2–3 mm diam, buds densely sericeous. Outer bark c. 0.1 mm thick, with reddish stripes on which pubescence near apex, becoming pale greyish or brownish and smooth when mature; inner bark c. 0.1 mm thick, blackish; wood pale brownish. Stipules triangular to subulate, 0.4–0.7 mm long, sericeous. Leaves clustered at the end of branchlets; petiole obtriangular and flat to slightly grooved above, 1–3 mm long, often glabrescent, lower side rounded and pubescent; blade oblanceolate or oblong, sometimes slightly asymmetric, 6–20 by 2.5–6 cm, membranous, base obtuse to cordate, without glands, margin distantly serrate, teeth falcate, apex acuminate or caudate, glabrous above, paler and more or less pubescent beneath; midrib slender, slightly raised on both sides, nerves 7–15 pairs, connected along margin, veinlets reticulate, obscure. Inflorescences bisexual, axillary, racemes, bracts to rachis stipule-like, main rachis 3–6 cm long, 0.25–0.5 mm diam, slightly pubescent, bracts lanceolate to oblong to linear, 1–2.8 by 0.3–0.5 mm, pubescent. Staminate flowers c. 4 mm diam; pedicel c. 2 mm long, c. 0.2 mm thick, pubescent; sepals oblanceolate or ovate, c. 1 by 0.6 mm, margin entire, ciliate, apex acute, outside pubescent; petals obovate, c. 1.8 by 1 mm, margin sometime ciliate, apex rounded, outer surface glabrous, inner rough and papillate; disc lobes semi-orbicular, c. 0.3 by 0.5, apex rounded; stamens 3, androphore c. 0.5 mm long, anthers free, ellipsoid, c. 0.5 mm long, opening yellowish, connectives dark reddish (when dried), with numerous droplets with secretion. Pistillate flowers c. 3.5 mm diam; pedicel slightly thickened towards apex, c. 4 mm long, apically c. 0.7 mm diam, accrescent when fruiting to up to 9 mm long and 1 mm diam, pubescent; sepals lanceolate, 1–1.5 by 0.5–0.7 mm, margin sometimes serrate, teeth glandular, apex acute, pubescent outside; petals as staminate flowers but caducous and slightly larger, 2–2.5 by 1–1.5 mm; disc lobes semi-orbicular, c. 0.55 by 0.45 mm, thin membranous, apex acute or rounded; ovary c. 0.8 mm diam, densely sericeous, style c. 0.1 mm long, almost indistinct, stigmas c. 0.5 mm long, completely bifid. Fruits c. 8 mm diam, finely pubescent; columella c. 4 mm long. Seeds not seen.

Map 10 Distribution of Trigonostemon scopulatus R.Y.Yu & Welzen (◆); T. serratus Blume (▼); T. sinclairii Jabl. (●); T. victoriae R.Y.Yu & Welzen (■); T. wetriifolius Airy Shaw & Ng (★); T. wildeorum R.Y.Yu & Welzen (▲).

Distribution — Java (endemic).

Habitat & Ecology — Rainforest. Flowering: November.

Note — The young branches are reddish (in dried specimens) and pubescent. The outer bark regularly sheds off, and reddish stripes remain. In older parts the branches become pale greyish or brownish.