Trigonostemon philippinensis Stapf

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 206-207

22. Trigonostemon philippinensis Stapf — Fig. 11 ; Map 9

Trigonostemon philippinensis Stapf (1907) 206; Pax & K.Hoffm. (1911) 91; Merr. (1923) 452; Airy Shaw (1981) 355; (1983b) 47; R.I. Milne (1995a) 27, in key, 29, in key. — Type: Elmer 8326 (holo PNH†; iso BO, G*, K, L), Philippines, Luzon, Laguna Prov., Los Baños.

Trigonostemon thrysoideus Stapf (1909) 264 (‘ thyrsoideum ’); Airy Shaw (1972a) 348; H.S. Kiu (1996) 166; Chantar. (2005) 29; (2007) 584, pl. 32: 1; P.T.Li & M.G.Gilbert (2008) 274. — Type: Henry 11947 (A*, K, NY*), China, Yunnan, Simao (Szemao).

[ Trigonostemon paniculatus Merr. ined., referred to by Jabl. (1963) 163 (as a synonym of T. sumatranus Pax & K.Hoffm. )].

Trees or treelets, 6–15(–20) m tall, dbh 6–25(–40) cm, flowering branches up to 6.5 mm thick, brownish, glabrescent, slightly scaberulous basally. Outer bark hard, 0.5–1 mm thick, brownish to greyish, rugose, lenticellate; inner bark 2–5 mm thick, pinkish to reddish, brownish (when dry); exudate clear, pinkish; wood dirty pinkish white. Stipules falcate, sometimes linear, up to 1.5–2 by c. 0.4 mm, pubescent near base, caducous. Leaves: petiole terete, 1.5–15 cm long, 0.8–2.5 mm diam, glabrous or slightly pubescent, base in apical leaves often somewhat sheathing; blade elliptic to sometimes obovate, 10–31 by 4–13.5 cm, coriaceous, base acute or cuneate, with 2 adaxial falcate glands, margin distantly serrate to crenate, teeth subulate or falcate, apex acuminate to caudate, sometimes acute, dark green above, pale green beneath, both sides glabrous or with a few very scattered hairs; venation often slightly pubescent, midrib slightly raised above and raised beneath, nerves 8–14 pairs, curved, branched and connected along margin, veins and veinlets reticulate, obscure. Inflorescences often terminal, paniculate, much branched and many-flowered, up to 30 cm long (up to 15 cm long in the Philippines), usually unisexual to bisexual, finely pubescent; bracteate under each node, bracts triangular, 0.5–2.5(–5) by 0.2–1 mm (larger ones basal in inflorescence, smaller ones higher up; often longer in Thai and Vietnamese specimens), outside pubescent, inside glabrous, on large branches sometimes caducous and often with 2 falcate or subulate bracteoles at the sides (Sumatra and Borneo), up to 1 mm long. Staminate flowers c. 5 mm diam; pedicel 3.5–4 mm long, c. 0.2 mm thick, pubescent, articulate at base; sepals elliptic or somewhat obovate, 1.2–1.6 by 0.6–0.8 mm, pale greenish or greenish yellow, base narrowed and connate, margin somewhat translucent, apex rounded or slightly undulate, outside pubescent, often with a gland in the middle, inside glabrous; petals obovate to spathulate, 2.5–4 by 1.2–2 mm, base cuneate to claw-like, entire, apex rounded, yellowish, sometime pale cream inside and with a paler margin ( Philippines), midrib and few parallel veins visible, glabrous; disc lobes trapezoid, 0.2–0.3 by 0.2–0.3 mm, c. 0.1 mm thick, fleshy, apex thickened, reflexed; stamens 3, androphore c. 0.5 mm long, free terminal part sometimes slightly trifid at top, sometimes bent (Sumatra and Borneo), anthers splitting off subapically from androphore, ellipsoid, c. 0.2 mm long, cream, divaricate (mainly in specimens from Thailand and Vietnam), connectives apically with droplets with secretion. Pistillate flowers of same size as staminate ones; pedicel 2.5–3.5 mm long, apex slightly thickened, 0.6–0.7 mm thick; sepals and petals as in staminate flowers; disc lobes rectangular, c. 0.4 by 0.6 mm, apex truncate; ovary c. 1 mm diam, glabrous and warty, styles extremely short, stigmas with a shallow groove above. Infructescence pendulous, dull pale light green. Fruits c. 1.5 cm diam, greenish, glabrous, warty or aculeate above; pedicel 2.5–4 cm long, green; sepals persistent but not accrescent; wall woody, c. 0.6 mm thick, exocarp partly detaching; columella c. 0.8 cm long. Seeds 6–7.5 mm diam, dark brown when dry; hilum long-triangular to heart-shaped, 1–2.5 by 0.5–1.2 mm.

Distribution — Thailand, Vietnam, Malay Peninsula, Sumatra, Borneo, Philippines.

Habitat & Ecology — Lowland evergreen to deciduous forests, sometimes on limestone hills, near rivers; growing on red to yellow calcareous soils to granite bedrocks. Flowering and fruiting: all year round.

Notes — 1. The inflorescences are mainly unisexual because they generally consist of flowers of the same gender but sometimes are mixed with a few flowers of the other sex. The flowers can spread evenly along secondary rachis, whereby the whole panicle attains a pyramid-shape ( Thailand and Vietnam), or the flowers cluster in brush- or broom-like groups on tertiary branches and the inflorescences seem more umbellate (Sumatra and Borneo).

2. Many collections (in many herbaria) of this species are incorrectly identified either as T. sumatranus or T. paniculatus (or ‘ T. paniculatum ’) for a historical reason.

Pax & Hoffman’s (1911) T. sumatranus was based on Forbes 2647 (BM, K, L), and is actually a synonym of T. viridissimus , a species that also bears paniculate inflorescences but can be easily distinguished from T. philippinensis by its much shorter petioles and stigmas being almost not bifid.

Merrill’s T. paniculatus ( ‘ paniculatum ’) ined. was based on rich collections, which are actually T. philippinensis , but he never published this name, because he thought T. paniculatus could be the same as T. sumatranus ( Jablonski 1963) .

Jablonski (1963) never saw Forbes 2647 and he misbelieved that T. sumatranus and T. paniculatus were conspecific, and therefore connected these two misperceptions, which explains these common misidentifications accordingly.

Figures

Map 9 Distribution of Trigonostemon philippinensis Stapf.

Fig. 11 Trigonostemon philippinensis Stapf, cultivated in Xishuangbanna Tropical Botanical Garden, Yunnan, China. a. Growing habit; b. leaf; c. bisexual inflorescence; d. staminate flower; e. young fruit. — Photos by Roderick Bouman.