Trigonostemon quocensis Gagnep.

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 41-42

24. Trigonostemon quocensis Gagnep. — sect. Tylosepalum — Map 6

Trigonostemon quocensis Gagnep.(1922) 753;(1925b) 316; Airy Shaw (1972) 348; Chantar. (2005) 27; (2007) 582. — Lectotype (designated here): Pierre s. n. (P, barcode P00717135; iso K, barcode K000959314, P, bar- codes P00717136, P00717138), Vietnam, Phu Quoc. — Other syntypes: Godefroy 739 (P, barcodes P00717131, P00717132), Vietnam, Ha-tien; Godefroy 740 (P, barcode P00717130), Vietnam, Ha-tien; Harmand 632 (P, barcodes P00717128, P00717129), Vietnam, Nui Cam; Pierre 6232 (G, barcode G00435097, MPU, barcodes MPU015001, MPU015002, NY, barcode NY00273345,P,barcodes P00717133, P00717134,P00717137), Vietnam, Chaudoc, Mount Pell.

Trigonostemon birmanicus Chakrab. & N.P.Balakr. (1984a) 175; N. P. Balakr. & Chakrab. (1991) 613, f. 2, syn. nov. — Type: Chin [collector’s name uncertain] 5849 (holo CAL, barcode CAL0000023654 ), Myanmar, Upper Chindwin , Numpakom drainage .

Shrubs or small trees, 0.5–5 m tall, dhb 6–8 cm; flowering branches 1–3.8 mm diam, pubescent when young, glabrous in old parts. Indumentum of simple hairs; translucent (oil?) dots sometimes present in green parts. Outer bark 0.1–0.2 mm thick, dark brown; inner bark 0.1–0.2 mm thick, reddish brown, solidified sap reddish black; wood yellow. Stipules subulate, 0.2–0.7 mm long, caducous, sometimes pubescent at base. Leaves: petiole terete, (0.6–) 1–6.1 cm long, 0.8–2 mm diam, glabrous or pubescent, sometimes thickened at apex and base; blade ovate to elliptic, 8–24 by 3.6–10 cm, chartaceous, base truncate, rounded, acute or sometimes cordate, 2 adaxial glands present, sometimes pubescent, margin distantly serrate, apex acuminate to caudate, both surfaces pubescent when young, glabrous when mature; venation triplinerved (basal secondary veins often as thick as other secondary veins), midrib and sometimes secondary veins flat or slightly raised above and distinctively elevated and pubescent beneath, other secondary veins 6–9 pairs, bow-shaped and connected along margin, tertiary veins scalariform, veinlets reticulate. Inflorescences bisexual, terminal or axillary, large panicles, pistillate flowers open before staminate ones; main axis terete, up to 44 cm long, 0.6–1.5 mm diam, pubescent; bracts linear to lanceolate, 1–12 by 0.15–1(–2.1) mm, often pubescent. Staminate flowers 4.4–5.5 mm diam, buds usually globose; pedicel 3.5–7.5 mm long, 0.15–0.3 mm diam, glabrous; sepals ovate to elliptic, 1.4–2.5 by 0.8–2.2 mm, base connate, margin entire, apex acute to rounded, pubescent outside; petals obovate to flabel- late, 2.1–3.9 by 1.7–2.5 mm, contort, yellow, lower part some- times claw-like, apex rounded, glabrous; disc annular, fleshy, margin entire, 0.4 (inner margin)– 0.8 mm (outer margin) diam; stamens 3, androphore 0.3–0.6 mm long, 0.2–0.3 mm diam, free part of filaments 0.4–0.5 mm long, anthers free, globose to ellipsoid, 0.4–0.5 mm long. Pistillate flowers 6–7 mm diam, buds somewhat conical; pedicel thickening toward apex, 2–5.5 mm long, apically 0.5–0.9 mm diam when flowering, elongating to 4–9 mm long, apically 0.6–1 mm diam when fruiting, pubescent; sepals lanceolate to elliptic, 1.5–4.5 by 0.7–1.6 mm, base connate, margin entire, apex acute to acuminate; petals and disc as staminate flowers; ovary 1–1.2 mm diam, densely pubescent, style indistinct, stigmas 0.4–1 mm long, slightly thickened and sometimes slightly bifid at apex. Fruits 1–1.1 cm diam, hirsute; sepals persistent, but not accrescent; wall 0.3–0.4(–0.5) mm thick, exocarp not detaching; columella 4.5–6.5 mm long. Seeds 6–7 mm diam, marbled; hilum orbicu- lar or rhombic, 1.2–1.7 by 1.1–1.5 mm.

Distribution — Myanmar (Upper Chindwin, in Sagaing or Kachin region), Thailand, Vietnam.

Habitat & Ecology — Understorey in dry evergreen forests, on limestone. Elevation: 140– 820 m. Flowering: all year round; fruiting: March, September.

Note — The species is relatively common in Thailand and Vietnam. Only two collections are known from Myanmar (Chin? 5849 and Griffith KD 4741). The plant sometimes has the similar translucent (oil?) dots in the green parts as T. eberhardtii . The staminate buds are usually globose (petals still contort), but in most other species they are often conical.

Figures

Map 6 Distribution of Trigonostemon eberhardtii Gagnep. (★), T. montanus R.Y.Yu & Welzen (▲), T. praetervisus Airy Shaw (■) and T. quocensis Gagnep. (X).