Trigonostemon verticillatus (Jack) Pax

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 213

29. Trigonostemon verticillatus (Jack) Pax — Map 11

Trigonostemon verticillatus (Jack) Pax in Pax & K.Hoffm (1911) 87; Jabl. (1963) 164; Airy Shaw (1972a) 349; Whitmore (1973) 136; Chantar. (2005) 30;(2007) 585,pl. 31: 2. — Enchidium verticillatum Jack (1822) 90; (1835) 257, excl. synon. Rumphius; Müll.Arg. (1866) 1256; Merr. (1952) 224. — Neotype (designated here): Maingay KD 1403 (holo L; iso BM, K), Malay Peninsula, Malacca (see note).

Telogyne indica Baill. (1858) 328, pl. 11, f. 13. — Trigonostemon indicus (Baill.) Müll.Arg. (1865) 214; (1866) 1107; Hook.f. (1887) 398; Ridl. (1924) 264; Jabl. (1963) 152. — Lectotype (designated here): Wallich 7997 (G; isolecto P), Malaysia, Penang.

Small trees, up to 8 m tall; flowering branches terete, 2.5–3 mm diam. Bark 0.4–0.5 mm thick, pale greyish; wood pale yellowish. Stipules subulate, 0.5–1.5 mm long, blackish and pubescent near base, yellowish at apex. Leaves: petiole wrinkled, terete but grooved above, 2 –9 cm long, often thickened at apex and base; blade oblong, sometimes elliptic or lanceolate, occasionally linear, 10–22 by (1.5–) 2.5–5 cm, chartaceous or coriaceous, base acute to rounded, 1 or 2 pairs of glands adaxially present, subulate or falcate, often glabrous, margin distantly serrate, teeth subulate, apex acuminate to caudate, upper surface dark green, lower surface pale green, both sides glabrous; midrib slightly raised above and distinctly elevated beneath, nerves 12 –21 pairs, connected along margin, veinlets reticulate, often obscure. Inflorescences bisexual, terminal or subterminal, racemes (spike-like) or thyrses, often puberulent, main rachis up to 10 cm long, involucral bracts triangular to lanceolate to falcate, 1–2 by c. 0.5 mm, with 2 lateral bracteoles; bracts to flowers broadly triangular, somewhat sheathing, up to 1 by 1 mm, apex acuminate, puberulent. Staminate flowers c. 4 mm diam (unopened); pedicel slightly thickened towards apex, 1.5–3 mm long, apically 0.6–0.8 mm diam, glabrous or very slightly puberulent; sepals often unequal, orbicular to ovate, 1–1.5 by 1–1.5 mm, imbricate, apex rounded, outside glabrous or slightly puberulent, margin ciliate; petals ovate, 2.5–2.8 by c. 2 mm, dark reddish, contort, apex rounded, outer surface glabrous, inner surface rough and slightly papillose, margin entire, occasionally slightly ciliate; disc annular when young and cupular when mature, c. 0.5 mm wide, margin often with 5 notches; stamens 5, androphore c. 0.5 mm long, anthers ellipsoid, c. 1 mm long, divaricate, connectives apically with numerous droplets (or expanded cells) with secretion. Pistillate flowers c. 5 mm diam; pedicel as staminate flowers but longer and thicker, c. 4 mm long, c. 1 mm diam; sepals elliptic, c. 1.5 by 1 mm when flowering, more or less accrescent to 3 by 2 mm when fruiting, apex rounded, outside slightly puberulent, margin ciliate; petals as staminate flowers, caducous; disc annular, subentire; ovary 1.2–1.5 mm diam, puberulent, style c. 0.2 mm long, sometimes indistinct, stigmas c. 0.7 mm long, bifid at apex, arms c. 0.5 mm long, thickened abaxially, reniform at base. Fruits c. 1 cm diam, outside finely puberulent; wall 0.7–1 mm thick, exocarp detaching. Seeds c. 5.5 mm diam; hilum rhombic, c. 1.8 by 1 mm.

Distribution — Vietnam, Thailand, Malay Peninsula.

Note — The genus Enchidium , described by Jack (1822), is reliably identical to Trigonostemon , even though there were a few mistakes in the manuscript, e.g., he mentioned that the plants have 10 stamens, instead of 5. The genus remained monospecific since Jack’s publication. Jack’s original collection from Sumatra was never checked again by later botanists and it is very likely that it does not exist anymore ( Merrill 1952). The illustration Jack cited (see Rumphius 1743) is a sterile plant and does not appear to be Trigonostemon .

Probably on account of the obscure status of Enchidium , botanists tended to abandon the name even though it was validly published prior to Trigonostemon . For example, Hooker (1887) regarded E. verticillatum as synonym under the later published T. indicus . Jackson (1893, 1895) reduced Enchidium as a synonym under Trigonostemon . Pax & Hoffmann (1911) also transferred the type species E. verticillatum to T. verticillatus and synonymised T. indicus under T. verticillatus . The genus was eventually rejected in 1954 (see Introduction).

Because Jack’s collection is not available and illustration is incorrect, a neotype is here designated to T. verticillatus . We followed Pax & Hoffmann’s (1911) treatment and the neotype specimen is chosen from one of Pax & Hoffmann’s (1911) vouchers.

Key to the varieties

1. Leaf blade oblong, elliptic or lanceolate, 10–22 by 2.5–5 cm. Petals with entire margin........ a. var. verticillatus