Trigonostemon hartleyi Airy Shaw

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 195

12. Trigonostemon hartleyi Airy Shaw — Map 1

Trigonostemon hartleyi Airy Shaw (1979) 535; (1980b) 206. — Type: Hartley 11087 (holo BRI *; iso L), Papua New Guinea, Morobe Dist., S of the Busu River, about 19 km N of Lae.

Small trees, up to 3.5 m tall; flowering branches terete, c. 3.8 mm diam, pale grey, young part appressed pubescent. Outer bark c. 0.1 mm thick, light grey, smooth; inner bark c. 0.1 mm thick, reddish; sap clear, yellowish; wood whitish. Stipules subulate, c. 1 mm long, pubescent at base. Leaves clustered at apex of branchlets; petiole terete but grooved above, 1.5–3 cm long, c. 1.5 mm diam, glabrescent or appressed pubescent near base and apex when young; blade elliptic to obovate, 14–20 by 5–8 cm, thin chartaceous, base and apex acute, base with two adaxial glands, often subulate or nipple-like, margin subentire or slightly crenate or dentate, teeth falcate or often obscure, above dark green, underneath pale green glaucous, both sides glabrous or slightly pubescent when young; midrib flat above, raised beneath, nerves 7–9 pairs, veinlets reticulate, very thin and obscure. Inflorescences: staminate ones c. 2 cm long, few-flowered; primary rachis c. 1 cm long, c. 1 mm thick, glabrous, 2 bracts at apex, c. 1 mm long, subglabrous; secondary rachis 7 mm long, slender and glabrous, apex with few bracts; pistillate inflorescences axillary, often only one open flower present apically, with a few depauperate flowers below; peduncles terete, up to c. 9 cm long, c. 0.8 mm thick, glabrous or slightly pubescent at base, bracteate on each node; bracts lanceolate or triangular, c. 1 by 0.5 mm, pubescent outside. Staminate flowers: pedicel slender, 4–5 mm long; sepals distinctly unequal, wide elliptic or obovate, 1–2 mm long, apex rounded, with few hairs outside; petals wide ovate, c. 3 by 2 mm, orange, base shortly claw-like, apex rounded; disc lobes suborbicular, c. 0.5 mm diam, flat, erect, solid, glabrous, entire, brownish when dry; stamens 5, androphore c. 0.5 mm long, anthers relatively large, ovoid, c. 0.5 mm long, erect, connectives very short. Pistillate flowers c. 7.5 mm diam; pedicel c. 3.5 cm long, thickened towards apex, up to 1.5 mm diam, glabrous; sepals oblong, 1.5–2 by c. 1 mm, not accrescent, apex rounded, greenish, outside slightly pubescent, with one conspicuous gland in the middle; petals not seen, caducous; ovary c. 3.5 mm diam, c. 3 mm high, stigmas 3, very shortly recurved. Fruits 12–15 mm diam, smooth, brownish. Seeds not seen.

Distribution — New Guinea (Morobe district, endemic).

Habitat & Ecology — Rainforest, growing on slope. Altitude: 150 m. Flowering and fruiting: January.

Note — Descriptions of the staminate inflorescences, staminate flowers and ovary are based on Airy Shaw (1979). Only known from the type, Hartley 12211 ( K, paratype) and a doubtful collections (Hartley 9811, K). The species is different from T. apetalogyne only by having 5 instead of 3 stamens (see also note under latter) .