Trigonostemon lanceolatus (S.Moore) Pax

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 37

15. Trigonostemon lanceolatus (S.Moore) Pax — sect. Trigonostemon — Map 3

Trigonostemon lanceolatus (S.Moore) Pax in Pax & K.Hoffm. (1911) 92. — Nepenthandra lanceolata S. Moore (1905) 149, pl. 471, f. 7–13. — Type: Beddome s.n. (BM, barcode BM000951502 ), Myanmar, Tenasserim [= Tanintharyi Region], Mooleyit slopes.

Trigonostemon phyllocalyx Gagnep. (1925a) 469; (1925b) 312; Airy Shaw (1972) 348; Chantar. (2005) 27; (2007) 581, syn. nov. — Type: Poilane 2700 (A, barcode A00048879 , P, barcodes P00717119 , P00717120 ), Vietnam,Annam, Nhatrang .

Trees, up to 5 m tall, dbh up to 5 cm; flowering branches 1.9–3.5 mm diam, pubescent when young, glabrous in old parts. Outer bark 0.1–0.2 mm thick, brown to pale or greyish brown; inner bark 0.1–0.2 mm thick, reddish brown, sap red; wood yellow to brown. Stipules subulate, 0.4–1.1 mm long, caducous, pubes- cent at base. Leaves: petiole terete, grooved above, 1.4–11.5 cm long, 0.8–2 mm diam, hirsute to glabrous; blade lanceolate to oblong, 6.8–21 by 2.3–8.2 cm, thick-chartaceous, base acute to rounded, 2 adaxial glands present, margin distantly serrate, apex acuminate to slightly caudate, both surfaces glabrous; venation pinnate, midrib flat or slightly raised above and elevated beneath, sometimes slightly pubescent beneath, secondary veins 6–10 pairs, curved, connected along margin, tertiary veins and veinlets reticulate. Inflorescences bisexual, often axillary, racemose thyrses, pistillate flowers open first, single per node near apex of axis, staminate flowers usually 1–3 per node below; axis up to 8.7 cm long, 0.5–0.8 mm diam, hirsute to glabrescent, bracts oblong, 0.4–6.5 by 0.1–1.4 mm, pubescent. Staminate flowers (bud) c. 2.4 mm diam; pedicel thickening toward apex, 1.8–2.5 mm long, apically 0.4–0.8 mm diam, slightly hirsute; sepals ovate to elliptic, 1.2–1.9 by 0.8–1.5 mm, base connate, margin entire, sometimes ciliate, apex rounded to acute, pubescent or hirsute outside; petals ovate to elliptic, 1.1–1.4 by 0.9–1.15 mm diam, glabrous, apex rounded; disc annular, c. 0.1 mm wide, ring c. 0.8 mm diam; stamens 3, androphore c. 0.1 mm long, anthers ellipsoid, 0.5–0.7 mm long, divaricate. Pistillate flowers 5–10 mm diam; pedicel thickening toward apex, 3–7 mm long, apically 1–1.2 mm diam, pubescent or hirsute; sepals triangular, 4–5.5 by 2.7–3 mm when flowering, significantly accrescent, up to 1.3 by 1.1 cm when fruiting, densely hirsute on both sides, base connate, margin mostly entire but with two teeth near apex, apex acuminate; petals elliptic, 2.5–3 by 1.8–2.6 mm, apex rounded; disc seemingly annular, c. 0.6 mm wide; ovary c. 1.7 mm diam, glabrous to hirsute; style absent; stigmas deeply bifid, 0.6–0.7 mm long, free arms V-shaped at base. Fruits 1–1.1 cm diam, densely hirsute, smooth; sepals persistent; wall 0.3–0.4 mm thick. Seeds c. 7.5 mm diam, marbled; hilum triangular, c. 2.5 by 1.7 mm.

Distribution — Myanmar (Tenasserim), Thailand (Chanthaburi), Vietnam ( Annam).

Habitat & Ecology — Evergreen forests, on rocky or sandy soil, near stream. Flowering: December to March; fruiting: December to January.

Note — The species is characterised by the much accres- cent and hirsute sepals in the pistillate flowers.

Figures

Map 3 Distribution of Trigonostemon bonianus Gagnep.(X), T. lanceolatus (S.Moore) Pax (▲), T. pachyphyllus Airy Shaw (★) and T. tuberculatus F.Du & Ju He (●).