Trigonostemon capitellatus Gagnep.

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 29

5. Trigonostemon capitellatus Gagnep. — sect. Tylosepalum — Map 1

Trigonostemon capitellatus Gagnep. (1922) 748; (1925b) 311. — Lectotype (designated here): Pierre 1323 (P, barcode P00717092; iso K, barcode K000959315, P, barcodes P00717090, P00717091, US 00433339), Viet- nam, Bien Hoa, towards Dongnai river near Tri Huyen. — Other syntypes: Thorel s. n. (P, barcode P00717089), Laos, Île de Khon; Pierre 472 (P, barcode P00717093), Vietnam, Bien Hoa, towards Dongnai river near Tri Huyen.

Trigonostemon cochinchinensis Gagnep.(1922) 748, syn.nov.;(1925b) 311. — Type: Pierre 1869 ( K, barcode K000959316 , P, barcodes P00717094 , P00717095 , P00717096 ), Vietnam, Bao Chiang .

Trigonostemon thorelii Gagnep.(1922) 755, syn. nov.; (1925b) 315. — Type: Thorel 2264 ( A, barcode A00048877 , P, barcodes P00648671 , P00648672 , P00717148 ), Laos, Stung Tréng à Kong .

Trigonostemon verrucosus J.J.Sm. (1924) 97, syn. nov. — Type: Bogor Botanical Garden VIII.E.16 (BO, sheets no. BO1298241, BO1298242, BO1298243, IBSC, barcode IBSC0306957, K, barcode K000959299, L, barcode L.2258669, SING, U, barcode U0002105), Java, cultivated in Bogor Botanical Garden.

Shrubs, 1.5–3m tall,dbh 2–3cm;flowering branches 1.3–3.7 mm diam, pubescent when young, glabrous in old parts. Indumentum of simple hairs; translucent (oil?) dots often present in green parts. Outer bark 0.1–0.2 mm thick, very finely rough- ened, brown, grey or black; inner bark 0.1–0.2 mm thick, dark red; wood pale yellowish, pith sometimes hollow. Stipules very small, often indistinct, pointing or subulate, 0.2–0.4 mm long, pubescent at base, caducous. Leaves: petiole terete but flat or slightly furrowed above, 0.3–2.3 cm long, 0.6–1.5 mm diam, pubescent; blade elliptic to oblong, 6–17.6 by 2–6.2 cm, chartaceous, base acute to rounded, 2 adaxial glands present, margin entire, apex acuminate to slightly caudate, upper sur- face glabrous, dark glossy green, lower surface more or less pubescent especially along venation and margin, bright light green; venation distinctly triplinerved, midrib and basal second- ary veins slightly raised above, distinctly elevated beneath, other secondary veins 3–6 pairs, veinlets reticulate, sometimes obscure. Inflorescences bisexual, often axillary panicles; main axis up to 21 cm long, 0.5–1 mm diam, green, pubescent; bracts lanceolate, up to 3 by 0.5 mm, pubescent. Staminate flowers 3.5–5.5 mm diam; buds conical; pedicels 2.5–4.4 mm long, 0.15–0.3 mm diam, glabrescent; sepals elliptic to somewhat rectangular, 0.6–0.8 by 0.5–0.7 mm, apex truncate or slightly emarginate, glabrescent outside, with an apical gland outside; petals obovate, 2–3.2 by 1.2–1.7 mm, pale light to dull ochreyellow, contort, apex rounded, glabrous; disc annular, 0.2–0.3 mm wide, 0.5–0.7 mm diam, glossy dark yellow, margin un- dulate, glabrous; stamens 3, androphore erect, 0.7–1.2 mm long, 0.1–0.15 mm diam, white, trifid at apex, free filament part 0.2–0.3 mm long, white, anthers free, subglobose, 0.35–0.6 mm long, cream. Pistillate flowers c. 5 mm diam; buds conical; pedicels as staminate flower but thickening toward apex, 5–7 mm long, apically 0.5–0.6 mm diam when flowering, accres- cent up to 1.5 cm long and 1.5 mm diam in fruit; sepals as in staminate flowers but sometimes lanceolate, apex sometimes acute, sometimes with more hairs, especially near gland; petals as staminate flowers but caducous when fruiting; disc as in staminate flowers; ovary 0.7–0.8 mm diam, glabrous and sometimes gibbose, style 0.1–0.2 mm long, stigmas 0.6–1 mm long, apically very slightly bifid and thickened. Fruits 0.95–1 cm diam, glabrous, more or less warty; sepals persistent but not accrescent; wall 0.3–0.5 mm thick, exocarp partly detaching; columella 3–5 mm long. Seeds 5.2–6.2 mm diam, dark brown- ish when dry, sometimes marbled, hilum oblong to orbicular, 0.6–1.2 by 0.3–0.9 mm.

Distribution — Cambodia, Laos, Vietnam.

Habitat & Ecology — Shaded understory in mixed evergreen, deciduous, seasonal or degraded hardwood forests. Growing on shale bedrocks. Elevation: c. 60 m. Flowering: March, July, September to October; fruiting: July, October.

Notes — 1. The species can be recognised by its distinctly triplinerved venation.

2.An illustration attached to one of the two syntypes of T. capitellatus ( Pierre 472, P, barcode P00717093) clearly shows a disc of 5 separate lobes in the pistillate flowers, while the other syntype ( Pierre 1323, P, barcode P00717090) and our own observations indicate otherwise: the disc in the pistillate flowers is annular but often with an undulate margin.

Figures

Map 1 Distribution of Trigonostemon adenocalyx Gagnep. (●),T. capillipes (Hook.f.) Airy Shaw (X), T. capitellatus Gagnep. (★), T. heteranthus Wight (▲) and T. kerrii Craib (■).