Trigonostemon filiformis Quisumb.

1. Trigonostemon filiformis Quisumb. View in CoL — sect. Trigonostemon — Fig. 1 View Fig ; Map 1 View Map 1

Trigonostemon filiformis Quisumb. (1930) 328, f. 7; R.Y. Yu & Welzen (2018) 194. — Lectotype (designated here): Clemens 16751 (NY*; iso A, UC*), Philippines, Luzon, Isabela Prov., Mt Moises.

Trigonostemon stenophyllus Quisumb. (1930) 330, f. 8; R.Y. Yu & Welzen (2018) 225. — Type: BS (Ramos & Edaño) 47331 (A, K, NY*, UC*), Philip- pines, Luzon, Isabela Prov., Mt Moises .

Shrubs, up to 1 m tall; branches terete, 2.2–3.5 mm diam, pubescent when young, glabrescent. Outer bark 0.1–0.2 mm thick, brown when young, grey when old, glabrous; inner bark 0.1–0.4 mm thick, dark brown, sap red, low quantity; wood pale yellow to brown. Stipules subulate, 0.5–0.8 mm long, pubes- cent, caducous. Leaves: petioles terete, 1–6.5 cm long, 1–2.8 mm diam, sometimes grooved above, slightly pubescent when young; blade oblong to lanceolate (to almost linear), 8–26.5 by 1–4.5 cm, coriaceous, base acute to rounded, 2 adaxial glands present, margin slightly distantly serrate, teeth falcate to subulate, apex acuminate, both sides reddish brown and pubescent when young, upper surface green, somewhat pale, glabrous, lower surface paler green and sparsely pubescent when mature; midrib flat above and elevated beneath, nerves 8–11 pairs, veinlets reticulate. Inflorescences unisexual (stami- nate) or bisexual, thyrsoid, terminal or axillary, staminate flowers clustered in glomerules, main rachis 3.5–4.5 cm long, 0.5–0.6 mm diam, almost glabrous; bisexual ones axillary, racemose, very slender, 6–11 cm long, 0.2–0.6 mm diam, slightly pubes- cent, often a pistillate flower at top, a few staminate flowers per node below; involucral bracts as stipules; bracts single per node, oblong, 3–9.5 by 0.6–2.2 mm, apex acuminate, green, both sides pubescent. Staminate flowers (bud) c. 4 mm diam; pedicel c. 3 mm long, c. 0.3 mm diam, light green, glabrous; sepals elliptic, 1.8–2.5 by 0.6–1.5 mm, white, base connate, margin entire, apex rounded, slightly pubescent outside; petals elliptic, 1.8–2.2 by 1–1.5 mm, dark purple, base cuneate, mar- gin entire, apex acute, both sides glabrous; disc lobes rectan- gular, 0.25–0.35 by 0.25–0.45 mm, apex truncate, c. 0.1 mm thick; stamens 3, androphore c. 0.3 mm long, anthers c. 0.8 mm long, apically divaricate. Pistillate flowers c. 4 mm diam; pedicel slightly thickened towards apex, 6.5–7.8 mm long, apically 0.6–0.9 mm diam (apex), pubescent; sepals oblong to lanceolate, 3.3–4 by 1.4–1.7 mm, margin entire, ciliate, apex acute to rounded, pubescent outside, glabrous inside; petals obovate, 4–5 by 2.1–2.9 mm, dark purplish, with a honey mark in the centre, base cuneately narrowed, margin entire, apex rounded, glabrous; disc lobes unequal, rectangular, 0.5 by 0.4–0.9 mm, white, apex truncate, corner rounded, glabrous; ovary c. 0.9 mm diam, densely pubescent; style 0.1–0.2 mm long; stigmas linear, 1.3–1.4 mm long, deeply bifid into 2 arms, each arm 0.9–1.1 mm long, slightly thickened near base. Fruits c. 1.2 cm diam, brown, sparsely puberulent, persistent sepals not accrescent; wall c. 0.35 mm thick, exocarp partly detaching. Seeds c. 7 mm diam.

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

Habitat & Ecology — In the Philippines, growing in forests, sometimes along riversides. Flowering: March to April.

Notes — 1. The description of the fruits is partly based on Quisumbing (1930). Trigonostemon filiformis was only known and described from the type collection from Mt Moises in the last revision ( Yu & Van Welzen 2018). We found specimens with young staminate flowers and mature pistillate flowers in the forest behind Casapsapan beach in Aurora Province (c. 95 km south of Mt Moises). The description (both vegetative and reproductive characters) has now been fully updated.

2. Trigonostemon stenophyllus was also a poorly known species from Mt Moises. The species was treated as a doubt- ful species because no staminate flowers were seen during the last revision ( Yu & Van Welzen 2018). It was considered different from T. filiformis by the broader leaves and thicker inflorescences. However, we found a continuous variation between the two species: the leaves can gradually vary from linear (as in the type of T. filiformis ) to oblong or lanceolate (as in the type of T. stenophyllus ), and the inflorescences can be very slender and pendulous (as in the type of T. filiformis ) or thicker and erect (as in the type of T. stenophyllus ). We therefore synonymized T. stenophyllus with T. filiformis . For illustrations of the typical T. stenophyllus and T. filiformis see Quisumbing (1930).

3. The species highly resembles T. villosus var. merrillianus (Airy Shaw) R.Y.Yu & Welzen , particularly in the glomerate staminate flowers, but the non-accrescent sepals in the pistillate flower appear to be a useful character to distinguish this species from the latter.