Trigonostemon kerrii Craib

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 36

13. Trigonostemon kerrii Craib — sect. Trigonostemon — Map 1

Trigonostemon kerrii Craib (1924) 97; Gagnep. (1925b) 321; Airy Shaw (1972) 346; Chantar. (2005) 25; (2007) 577. — Lectotype (designated by Chantaranothai 2005): Kerr 5871 (BK*, barcode BK239811 ;iso A*, barcode A00048870, P, barcode P04810877), Thailand, Nakawn Tai.

Shrubs or small trees, 2–3 m tall; flowering branches 1.5–2.8 mm diam, pubescent when young, glabrous in old parts. Outer bark 0.1–0.2 mm thick, pale grey to brown; inner bark c. 0.1 mm thick, dark reddish; wood pale yellowish to white. Stipules subulate, 0.5–1 mm long, caducous, pubescent at base. Leaves: petiole terete but grooved above, 0.7–2.8 cm long, 0.9–1.2 mm diam, slightly pubescent; blade oblong to oblanceolate, 10.5–21 by 1.8–4.4 cm, chartaceous, base acute, with 1–2 pairs of adaxial glands, margin distantly serrate, teeth glan- dular, apex acuminate, upper surface glabrous, lower surface glabrescent; venation pinnate, midrib slightly raised above and elevated beneath, slightly pubescent beneath, secondary veins 8–11(–16) pairs, curved and connected along margin, tertiary veins reticulate, often obscure. Inflorescences seemingly unisexual, subterminal; staminate ones racemose thyrses, pistillate ones racemes; axis 1–11.2 cm long, 0.4–0.75 mm diam, pubescent; bracts lanceolate, 0.5–3.6 by 0.2–0.9 mm, pubescent. Staminate flowers c. 2.8 mm diam; pedicel 2.5–6 mm long, 0.1–0.2 mm diam, glabrescent; sepals elliptic to lan- ceolate, 0.9–1.5 by 0.5–0.9 mm, base connate, margin often serrate, apex acuminate to rounded, pubescent outside; petals in flower bud elliptic, 1.1–1.4 by 0.7–0.9 mm, apex rounded, purplish red ( Craib 1924); disc glands 5, c. 0.15 by 0.1 mm; stamens 3, androphore indistinct (flower too young), anthers ellipsoid, 0.7–0.8 mm long. Pistillate flowers (bud) c. 1.7 mm diam; pedicel c. 2.6 mm long, 0.4–0.5 mm diam, glabrescent; sepals triangular, 1.6–1.9 by 0.7–0.9 mm, base connate, margin fringed with capitate glands, apex acuminate; petals elliptic, 1.7–2.2 by 1–1.3 mm, apex rounded, purplish red ( Craib 1924); disc glands 5, c. 0.2 by 0.2 mm; ovary c. 0.7 mm diam, glabrous, style absent, stigmas c. 0.25 mm long, apically seem- ingly bifid. Fruits glabrous; pedicel c. 1.8 cm long, c. 0.7 mm diam, glabrescent; sepals accrescent, persistent, lanceolate, 5–6 by 1.5–2 mm, margin fringed with capitate glands; wall 0.3–0.4 mm thick, exocarp not detaching; columella c. 3 mm long. Seeds not seen.

Distribution — Thailand, Cambodia (Kampong Thom).

Habitat & Ecology — In evergreen forests. Elevation: 100– 200 m. Flowering: March; fruiting: April.

Note — The species resembles T. heteranthus in the pistillate sepals with a fringed margin with capitate glands, but it has a shorter petiole and shorter inflorescences, purplish red petals (vs white in T. heteranthus ) and bifid stigmas (vs not bifid in T. heteranthus ).

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 (■).