Trigonostemon murtonii Craib

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 40

20. Trigonostemon murtonii Craib — sect. Trigonostemon — Map 8

Trigonostemon murtonii Craib (1911) 464 (‘ murtoni ’); Pax & K.Hoffm. (1912) 128; Airy Shaw (1972) 347; Chantar.(2005) 26;(2007) 581. — Type: Murton 18 (K, barcode K000959311), Thailand, west coast, Koh Klone.

Trigonostemon pierrei Gagnep. (1922) 752; (1925b) 321, syn. nov. — Type: Pierre 1530 (A*, barcode A00048875 ,K,barcode K000959307 ,P,barcodes P00717121 , P00717122 , P00717123 , US *, barcode US 00096541), Viet- nam, Phu Quoc , Mt Ong Chao.

Trigonostemon pinnatus Gagnep. (1922) 752; (1925b) 318. — Type: Pierre s.n. ( K, barcodes K000959309 , K000959310 , P, barcodes P00717124 , P00717125 , P00717126 , NY *, US*), Vietnam, Cochinchina, prov. de Bien Hoa, Mt Lap-vo

Shrubs, 1–5 m tall; flowering branches 1.1–3.5 mm diam, pubescent when young, glabrous in old parts. Outer bark c. 0.1 mm thick, dark brown to pale grey; inner bark c. 0.1 mm thick, red- dish brown; wood pale yellowish. Stipules subulate, 0.3–0.7 mm long, caducous, often pubescent at base. Leaves: petiole terete, grooved above, 0.2–1.9 cm long, 0.7–1.5 mm diam, pubescent; blade oblanceolate to oblong, 5–20 by 1.2–4.3 cm, chartaceous to coriaceous, base rounded to acute, 2 adaxial glands present, margin entire, occasionally with glandular or subulate teeth, apex acuminate to short-caudate, both sur- faces glabrous; venation pinnate, midrib elevated on both sides, sometimes furrowed above, often sparsely pubescent beneath, secondary veins 9–18 pairs, curved, bifurcate and connected along margin, tertiary veins reticulate, obscure. Inflorescences bisexual, terminal or axillary racemes (flowers clustered at apex) or panicles (spreading like a broom at apex); peduncle up to 7 cm long, 0.3–0.7 mm diam, pubescent; bracts oblong to lanceolate, 1–8.5 by 0.2–1.5 mm, pubescent on both sides. Staminate flowers 3–5 mm diam; pedicel 3–4.5 mm long, 0.1–0.2 mm diam, pubescent; sepals elliptic, 0.8–1.5 by 0.5–0.8 mm, base connate, margin entire, apex acuminate, acute, rounded or bilobed, pubescent outside; petals obovate to spathulate, 1.6–2.7 by 1–2 mm diam, dark pink, glabrous, apex rounded; disc glands 5, 0.3–0.35 by 0.1–0.15 mm; sta- mens 3, androphore c. 0.5 mm long, c. 0.25 mm diam, anthers ellipsoid, 0.4–0.5 mm long, connective with droplets (expanded cells) with secretion. Pistillate flowers 3.3–8 mm diam; pedicel thickening toward apex, 3.5–7 mm long, apically 0.5–1 mm diam, elongating to c. 1 cm long in fruit, pubescent; sepals lan- ceolate, 5–6 by 1–1.6 mm, slightly accrescent to c. 8 by 2.2 mm when fruiting, pubescent outside, especially along midrib, base connate, margin entire, apex acuminate; petals as in staminate flowers; disc lobes rectangular, 0.2–0.25 by 0.25–0.3 mm, apex truncate; ovary 0.6–1.3 mm diam, densely pubescent; style indistinct, less than 0.1 mm long; stigmas apically deeply bifid, free arms coiled. Fruits (young) pubescent. Seeds not seen.

Distribution — Thailand, Cambodia, Vietnam.

Habitat & Ecology — Evergreen forests, on sandy clay. Elevation: c. 250 m. Flowering: February, April, June, November; fruiting: April.

Note — The inflorescences are often racemose when young and start branching and become apically broom-like when older. In this character it resembles T. scopulatus R.Y.Yu & Welzen , but that species has a much longer petiole.

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).