Trigonostemon merrillii Elmer

Yu, R. - Y., Agoo, E. M. G., Callado, J. R. & Welzen, P. C. van, 2020, Taxonomic notes on Trigonostemon (Euphorbiaceae) in the Philippines, Blumea 65 (1), pp. 12-24 : 16-20

3. Trigonostemon merrillii Elmer — sect. Spinipollen R.Y.Yu & Welzen — Fig. 3 ; Map 1

Trigonostemon merrillii Elmer (1911) 1304; Pax & K.Hoffm.(1914) 407; Merr. (1923) 452; Airy Shaw (1983) 47;R.Y. Yu & Welzen (2018) 203. — Lectoype (designated here): Elmer 12819 (L; iso BISH*, BM, BO,F*, G*, HBG*,MO*, NY*, US *), Philippines, Palawan, Puerto Princesa (Mt Pulgar).

Small trees, 1.5–3 m tall, stem up to 2.5 cm diam, hardly branching. Indumentum densely sericeous, especially on young parts. Outer bark 0.1–0.2 mm thick, pale brownish, sericeous; inner bark 0.3–0.4 mm thick, white to pale yellow, sometimes black when sap is solidified, sap translucent when fresh; wood white to pale yellow; pith sometimes empty. Stipules lanceolate to linear, 1–3 mm long, base sericeous, caducous. Leaves: petioles terete, often wrinkled when dry, 1–5.5 cm long, 2–6.7 mm diam, densely sericeous; blade elliptic, lower half often cuneately nar- rowing, 10–46.5 by 7–11.9 cm, chartaceous, base rounded, 2 adaxial glands present but often caducous or covered by silky hairs, margin distantly serrate, teeth often apiculate, falcate when young, apex acute to acuminate to caudate, upper surface greenish, paler beneath, both sides covered by long silky hairs; midrib slightly raised above and much elevated beneath, more densely sericeous, nerves 10–13(–17) pairs, curved and connected near margin, veins and veinlets reticulate, sometimes obscure. Inflorescences bisexual or unisexual, paniculate thyrses, up to 31 cm long, 0.4–1.6 mm diam, sericeous; involucral bracts as stipules, nodal bracts lanceolate, variable in size, petiole up to 0.7 cm long, blade 0.4–3.6 by 0.1–0.7 cm, sericeous; staminate flowers partly single and ramiflorous, others glomerate, pistillate flowers single, above or below the staminate ones. Staminate flowers 2.8–4.5 mm diam; pedi- cel 1.5–4.6 mm long, 0.1–0.2 mm diam, pink, glabrescent; sepals unequal, orbicular to elliptic to spathulate, 0.9–1.4 by 0.5–1.2 mm, pink to red in the centre, base connate, margin entire or slightly undulate, apex acute to rounded, more or less pubescent outside; petals spathulate to flabellate, 2–2.9 by 1.5–2.4 mm, dark purple to black, without honey mark, base claw-like, apex rounded to truncate to sometimes slightly bilobed, glabrous on both sides; disc annular, c. 0.25 mm diam (inner margin), c. 0.1 mm thick, red; stamens 3, androphore erect, 0.4–0.5 mm long, anthers ellipsoid, 0.4–0.6 mm long, white, gathered on the top of androphore, slightly divaricate at apex, connective apically with some droplets (expanded cells) with secretion. Pistillate flowers (bud) c. 2 mm diam; pedicel 3.5–4.5 mm long, 0.35–4 mm diam (apex), sericeous; sepals elliptic, 1.8–2.2 by 0.7–1.5 mm, entire, apex acute, sericeous outside; petals spathulate, 1.6–2.1 by 1.1–1.2 mm, base cune- ate, somewhat claw-like, apex rounded, both sides glabrous; disc lobes annular, less than 0.1 mm thick; ovary c. 0.6 mm diam, smooth or slightly warty, style indiscernible, stigmas partly bifid, arms c. 0.1 mm long, each pair horseshoe-shaped. Fruits c. 1.25 cm diam, slightly warty; pedicel 1.15–1.35 cm long, 1.2–1.3 mm diam (apex), sepals persistent, not much accrescent, red; columella c. 4 mm long. Seeds streaked or conspicuously mottled.

Distribution — Philippines (endemic).

Habitat & Ecology — Lowland dipterocarp forest. Altitude: 15–80 m. Flowering: March.

Note — The first author’s (RYY) field observations have provided some new insights for the species: the leaves are clustered at the top of the main branch and the inflorescences can develop into a panicle when mature. The spathulate petals with a claw-like base strongly resemble those of the other species in sect. Spinipollen, e.g., T. longifolius Baill. , T. oblongifolius Merr. The species is known from Palawan and Mindanao. The diameter of fruits is based on Elmer (1911).

Figures

Map 1 Distribution of Trigonostemon filiformis Quisumb. (●), T. merrillii Elmer (▲), T. palustris R.Y.Yu & Welzen (■) and T. victoriae R.Y.Yu & Welzen (★).

Fig. 3 Trigonostemon merrillii Elmer, from Mt Saint Paul, Puerto Princesa, Palawan, the Philippines. a. Growing habit; b. main branch with cauliflorous flowers; c. part of paniculate inflorescence with only staminate flowers; d. pistillate inflorescence; e. bisexual inflorescence, pistillate flower at top; f. bisexual inflorescence, pistillate flower at bottom; g. translucent sap; h. staminate flower, lateral view; i. staminate flower, top view; j. juvenile pistillate flower; k. fruit, back side; l. fruit, front side — Photos by: a, k–l: Danilo Tandang; b–j: Ren-Yong Yu.