Trigonostemon filiformis Quisumb.

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 194

10. Trigonostemon filiformis Quisumb. — Map 3

Trigonostemon filiformis Quisumb. (1930) 328, f. 7. — Type: M. S. Clemens 16751 (holo PNH†; iso A, NY*, UC*), Philippines, Luzon, Isabela Prov., Mt Moises .

Small trees; flowering branches 1.5–3.5 mm diam. Outer bark c. 0.1 mm thick, brownish to greyish, smooth, pubescent in young parts; inner bark c. 0.1 mm thick, reddish, sap light red; wood yellow or white. Stipules small, subulate, 0.5–1 mm long, pubescent. Leaves: petiole 1–3(–4.5) cm long, 0.6–1 mm diam, terete, sometimes angled, or furrowed above, pubescent; blade linear to long lanceolate, 13–22 by 0.8–1.5 cm, chartaceous, base acute to cuneate, with 2 adaxial, falcate glands, margin distantly serrate, teeth glandular, apex acuminate to caudate, upper surface dark green, glabrous, lower surface paler, softly appressed pubescent; midrib plain above and slightly raised and densely pubescent beneath, nerves obscure, 10–13 pairs, curved to almost right angled, connected, pubescent beneath, veins reticulate, very vague. Inflorescences terminal or axillary, racemes or thyrses (but often only 1 flower developed on each node); rachis slender, 2–6(–13) cm long, 0.15–0.4 mm diam, pubescent; bracts lanceolate or oblong, 2–10 by 0.3–1.3 mm, slightly pubescent. Staminate flowers: sepals obovate to round, c. 1.5 by 0.5 mm; petals c. 2 by 1.25 mm diam; disc unknown; stamens 3, anthers sessile, erect, globose. Pistillate flowers 3.5 (unopen)–7.5 (post-anthesis) mm diam; pedicels slightly thickened towards apex, 6–9 mm long, apically 0.8–1.1 mm diam, pubescent; sepals elliptic, 2.3–3 by 0.8–1.2 mm, accrescent to at least 9 by 2.2 mm, pubescent outside; petals oblong to oblanceolate, c. 4 by 1.25–1.5 mm, purple, glabrous; disc unknown; ovary at least 0.7 mm diam, densely pubescent; styles often indistinct, trifid; stigmas deeply bifid into 2 arms, each arm 0.6–1.2 mm long. Fruits and seeds unknown.

Distribution — Borneo (Sabah) and Philippines (Luzon).

Habitat & Ecology — Lowland forest edge, ultramafic soil in Sabah. Flowering: April and December.

Notes — 1. The staminate flowers are not seen by us. The description is based on Quisumbing (1930).

2. The species is distinct from T. verticillatus var. salicifolius by the staminate flowers with 3 instead of 5 stamens. Another useful character is that T. verticillatus var. salicifolius often has two pairs of adaxial glands at leaf base, whereas T. filiformis always has one.

3. The type was collected from Mt Moises of the Philippines, as was the type of T. stenophyllus Quisumb. Both these two species are poorly known and probably they are conspecific, but this cannot be confirmed until further material is available of both species .