Trigonostemon fragilis (Gagnep.) Airy Shaw

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 33-35

10. Trigonostemon fragilis (Gagnep.) Airy Shaw — sect. Tylosepalum — Map 8

Trigonostemon fragilis (Gagnep.) Airy Shaw (1978) 415. — Poilaniella fragilis Gagnep. (1925a) 467; (1925b) 307; P.T. Li et al. (2006) 119; P.T.Li & M.G.Gilbert (2008) 274. — Lectotype (designated here): Poilane 2927 (P, barcode P00712172;iso A*, barcode A00106974,P, barcodes P00712173, P00712174), Vietnam, Annam, Tre Island, near Nhatrang.

Shrubs, 2–3 m tall; flowering branches 1.1–2.5 mm diam, pu- bescent when young, glabrous in old parts. Outer bark 0.1–0.2 mm thick, pale brown to grey; inner bark 0.1–0.3 mm thick, pale to reddish brown; wood pale yellowish to brown. Stipules subulate, 0.2–0.5 mm long, caducous, often indistinct, pubes- cent at base. Leaves: petiole terete, grooved above, 0.5–2.4 cm long, 0.5–1 mm diam, glabrescent; blade elliptic to ovate, 1.8–5.5 by 1.2–3 cm, chartaceous, base acute to rounded or sometimes truncate, 2 adaxial glands present, margin entire, apex acute or rounded, both surfaces glabrescent, particularly pubescent within the axils of midrib and lateral veins and one or more domatia sometimes present; venation triplinerved, midrib and basal secondary veins flat or slightly raised above and elevated beneath, other secondary veins 3–4 pairs, curved and connected along margin, tertiary veins reticulate, often obscure. Inflorescences seemingly unisexual, terminal or axillary, cymes or thyrses; axis terete, 1–3.8 cm long, 0.4–0.7 mm diam, gla- brescent; bracts lanceolate to oblong, 0.2–1 by 0.2–0.5 mm, pubescent outside. Staminate flowers (bud) c. 2.4 mm diam; pedicel 6.4–7.5 mm long, slightly thickening toward apex, 0.3–0.7 mm diam, slightly pubescent; sepals elliptic, unequal, 1.2–2.1 by 0.9–1.5 mm, margin entire, apex rounded, pubes- cent outside; petals flabellate, but elliptic when young, 1.5–1.6 by 1–1.4 mm, apex sometimes slightly bilobed; disc annular, c. 0.2 mm wide; stamens 3, androphore erect, c. 0.1 mm long, anthers ellipsoid, 0.8–0.9 mm long. Pistillate flowers (flattened) c. 1 cm diam; pedicel slightly thickening toward apex, 7.3–10 mm long, apically 0.5–0.7 mm diam; sepals elliptic, 1.6–3.2 by 0.9–1.4 mm, margin entire, apex acute, pubescent outside; petals flabellate, 3.2–5 by 3.2–5.4 mm, apex slightly bilobed; disc annular, 0.2–0.3 mm wide; ovary 0.7–1 mm diam, glabrous, style absent, stigmas 0.4–0.55 mm long, thickened and with a very shallow groove at apex. Fruits 1.2–1.3 cm diam, glabrous; wall 0.7–1 mm thick, exocarp 0.3–0.6 mm thick, completely detached; columella 7.1–7.8 mm long. Seeds flattened globose, 10–10.5 by 9–9.5 mm, hilum oblong, 2.3–2.4 by 1.1–1.5 mm.

Distribution — China (Hainan?), Vietnam (Ninh Hai District, Ninh Thuan Province).

Habitat & Ecology — In forests, dry and level lands, or near salt fields or lakes; on sandy soil or clay. Flowering: April; fruit- ing: January, April.

Note — This is the only species in Trigonostemon with domatia in some leaves.

Figures

Map 8 Distribution of Trigonostemon fragilis (Gagnep.) Airy Shaw (●), T. lii Y.T.Chang (★), T. murtonii Craib (▲), T. villosus Hook.f. var. nicobaricus (Chakrab.) N.P. Balakr. & Chakrab. (■) and T. xyphophylloides (Croizat) L.K.Dai & T.L.Wu (X).