Trigonostemon apetalogyne Airy Shaw

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 185-187

1. Trigonostemon apetalogyne Airy Shaw — Map 1

Trigonostemon apetalogyne Airy Shaw (1979) 534; (1980b) 206. — Type: Kostermans & Soegeng 340 (holo K; iso BO, L), [ Indonesia,] W Papua, limestone hills E of Sukarnapura (= Hollandia = Djajapura), Polima I .

Small trees, at least 2.5 m tall, stem at least 4 cm diam; flowering branches c. 3 mm diam. Outer bark c. 0.15 mm thick, smooth, dark brown to grey, appressed pubescent on young parts; inner bark c. 2 mm thick, blackish; wood reddish brown. Stipules subulate to falcate, 0.8–1 mm long, base pubescent, apex slightly bent. Leaves: petiole terete but grooved above, 2.5–5 cm long, slightly pubescent to glabrescent, slightly thickened at both base and top; blade oblanceolate, 11–20 by 3.5–7 cm, chartaceous to coriaceous, base narrow-rounded, with 2 adaxial glands, margin distantly serrate, apex acuminate, both sides glabrous (very sparsely pubescent when young); venation penninerved, slightly pubescent on lower side when young, midrib flat above and elevated beneath, secondary nerves 9–12 pairs, small veins reticulate, often obscure. Inflorescences: unisexual; staminate flowers cauliflorous; pistillate inflorescences subterminal, up to 14 cm long, paniculate (one side branch), few-flowered at the apex of the branches; bracts lanceolate, 0.8–2 by 0.4–0.9 mm, apex acuminate, pubescent outside. Staminate flowers c. 5 mm diam; pedicel 3–5 mm long, glabrescent; sepals ovate to orbicular, 1–1.2 by 0.6–0.7 mm, glabrescent outside; petals elliptic to obovate, 2–2.5 by 1.2–1.8 mm, entire, dark yellow, glabrous; disc glandular; stamens 3, androphore 0.3–0.5 mm long, filaments 0.1–0.2 mm long, anthers ellipsoid, c. 0.2 mm long. Pistillate flowers withered (post-anthesis), c. 2.5 mm diam; pedicel c. 7 mm long and 0.8 mm diam (top) when flowering, slightly thickened towards apex, in fruit accrescent to c. 1.5 cm long and 1.3 mm diam (top),

Map 1 Distribution of Trigonostemon apetalogyne Airy Shaw (●); T. hartleyi Airy Shaw (★).

glabrescent; sepals elliptic, 1.5–2 by 0.5–1 mm, glabrescent; petals not seen; disc as staminate flowers; ovary c. 1 mm diam, glabrous; style indiscernible; stigmas c. 0.6 mm long, apically flattened and slightly bifid. Fruits and seeds unknown.

Distribution — New Guinea (endemic).

Habitat & Ecology — On limestone hills. Altitude: c. 100 m. Flowering and fruiting: August.

Notes — 1. The species is only known from the type collection. The specific epithet indicates that the pistillate flowers lack petals, but this is very unlikely, because the petals are generally early cauducous in Trigonostemon and the specimen only has old flowers.

2. Trigonostemon apetalogyne differs from T. hartleyi only by having 3 instead of 5 stamens.

3. This species is also similar to T. villosus var. borneensis in leaf shape and cauliflorous staminate flowers, but we still keep it separate because of its dark yellow flowers (as recorded on the type collection; vs dark purplish in T. villosus var. borneensis ) and branched pistillate inflorescences (vs not branched in T. villosus var. borneensis ).