Trigonostemon eberhardtii Gagnep.

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 31

8. Trigonostemon eberhardtii Gagnep. — sect. Tylosepalum — Fig. 1 ; Map 6

Trigonostemon eberhardtii Gagnep. (1922) 749; (1925b) 313. — Lectotype (designated here): Bon 5239 (P, barcode P00717103), Vietnam, Annam, Thanh-hoa. — Other syntypes: Eberhardt 4293 (P, barcodes P00717101, P00717102), Vietnam, Tonkin, Hoa-binh, Mai-ha; Bon 5465 (P, barcodes P00717099, P00717100), Vietnam, Annam, Son-thôn.

Trigonostemon harmandii Gagnep. (1922) 750; (1925b) 313. — Type: Harmand 2956 ( P, barcodes P00648665 , P00648666 , P00648667 ), Cambodia .

Trigonostemon poilanei Gagnep. (1922) 753; (1925b) 314. — Type: Poilane 40807 ( A, barcode A00048878 , P, barcode P00717127 ), Vietnam, Bien- hoa, Giaray .

Trigonostemon albiflorus Airy Shaw (1971) 547; (1972) 345; Chantar.(2005) 23; (2007) 574, f. 92; P.T.Li & M.G.Gilbert (2008) 273. — Trigonostemon leucanthus Airy Shaw var. siamensis H.S.Kiu in Kiu & Chen (1992) 211.— Type: Winit 1704 (holo K, on 2 sheets,barcodes K000959303,K000959304; iso BK, barcode BK257891 , BM, barcode BM000951503), Thailand, Lampang, Mê Pêng.

Trigonostemon leucanthus Airy Shaw (1971) 548; H. S. Kiu (1996) 164. — Type: Morse 668 ( K, barcodes K000959336 , K000959337 ), China, Guangxi, Longzhou .

Trigonostemon wui H.S. Kiu (1995) 19, f. 2. — Type: Kiu [H. X. Qiu ] 451 (holo IBSC, not found; iso IBK, barcode IBK00190788 ), China, Guangdong, Fengkai, Yulao .

Shrubs or small trees, 1–5(–7) m tall, dbh 2.8–6.3 cm; flowering branches 1.1–5 mm diam, pubescent when young, glabrous in old parts. Indumentum of simple hairs; translucent (oil?) dots often present in green parts (and sometimes petals). Outer bark c. 0.1 mm thick, dark to pale brown or greyish brown; inner bark 0.1–0.2 mm thick, brown to reddish brown; wood white to pale yellowish. Stipules subulate, 0.3–0.7 mm long, caducous, often pubescent. Leaves: petiole terete, grooved or flat above, 0.5–8 cm long, 0.7–2.1 mm diam, glabrous or pubescent; blade elliptic, 8.5–26 by 2.5–8 cm, chartaceous, base acute, 2 adaxial glands present, occasionally sparsely pu- bescent, margin entire or very distantly serrate, apex acuminate to caudate, upper surface glabrous, dark green, lower surface often very sparsely pubescent, pale green; venation triplinerved, midrib (and sometimes 2 basal secondary veins) slightly raised above and distinctively elevated beneath, pubescent on lower surface, especially near base, other secondary veins 4–7(–10) pairs, bow-shaped and connected along margin, tertiary veins scalariform, veinlets reticulate. Inflorescences bisexual, terminal or axillary, paniculate, pistillate flowers open before staminate ones; main axis terete, up to 31.5 cm long, 0.4–2.7 mm diam, pubescent to glabrous; bracts linear to lanceolate to triangular, 0.7–2.7 by 0.3–0.6 mm, pubescent outside; bracteoles linear to lanceolate, 0.4–0.7 by 0.1–0.2 mm, densely pubescent. Staminate flowers 6–8 mm diam; buds conical; pedicel 2–9.5 mm long, 0.15–0.3 mm diam, glabrous, light green; sepals elliptic, 1–2.3 by 0.5–0.7 mm, light green, base connate, mar- gin entire, apex acute, often with a short notch and an adaxial gland, pubescent outside; petals obovate, 2.8–5 by 1.5–3 mm, contort, membranous, white, lower part cuneately narrowed, apex rounded, glabrous; disc annular, yellow, margin undulate, often deeply notched, 0.4 (inner margin)– 0.6 mm (outer mar- gin) diam; stamens 3, androphore 0.9–1.2 mm long, 0.1–0.2 mm diam, white, free part of filaments c. 0.2 mm long, white, anthers free, globose to ellipsoid, 0.3–0.4 mm long, yellow. Pistillate flowers 6–9 mm diam; buds conical; pedicel slightly thickening toward apex, 3–15.5 mm long, apically 0.45–1.1 mm diam when flowering, glabrescent; sepals as staminate flowers but larger, 1.3–3.8 by 0.6–1.3 mm, apex often with an adaxial gland but without notch; petals as staminate flowers; disc lobes 5, rectangular, 0.3–0.45 by 0.3–0.4 mm, yellow, apex truncate; ovary 1–1.1 mm diam, glabrous, green, style 0.1–0.2 mm long, stigmas 0.8–1.1 mm long, bent, white, apically slightly thickened and slightly bifid. Fruits 1.1–1.5 cm diam, greenish, glabrous; pedicel 1.9–3.4 cm long, 1.2–1.8 mm diam; sepals persistent but not accrescent; wall 0.4–0.5 mm thick, exocarp partly detaching; columella 4.5–6.5 mm long. Seeds 7–8 mm diam, marbled; hilum rhombic, 2.5–3 by 1–2 mm.

Distribution — China, Thailand, Laos, Cambodia, Vietnam.

Habitat & Ecology — Evergreen or deciduous forests, growing on limestone, sometimes in shaded areas near rivers. Elevation: 150–1300 m. Flowering: March to December; fruiting: May to December.

Notes — 1. Trigonostemon eberhardtii is characterised by the translucent (oil?) dots and white petals (the label of a specimen from Thailand, Sangkhachand 531, indicates that the petals are yellow, but this is a very exceptional case and the label could be wrong).Although the dots are not always present in all green parts (young branches, petiole, leaf blade, inflorescences, sepals, ovary and fruits), when present, it is a good spotting character, particularly in herbarium material.

2. The species resembles T. viridissimus , with which the morphological boundary is sometimes unclear. However, the molecular phylogeny (Yu et al. 2019) shows that the two spe- cies are placed in different subclades within sect. Tylosepalum . Main characters that can be used in identification include: 1) the white petals (yellow to orange in T. viridissimus ); 2) monopodial branching in the inflorescences with relatively more condensed staminate flowers (vs sympodial branching and relatively loose panicles in T. viridissimus var. viridissimus ); and 3) an indistinc- tive style (shorter than 2 mm in T. eberhardtii ; up to 6 mm in T. viridissimus ).

Figures

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

Fig. 1 Trigonostemon eberhardtii Gagnep., private collection of Hua-Shing Kiu, originally from Yulao, Fengkai, Guangdong, China. a. Growing habit; b. leaf base, showing glands; c. top view of staminate flower; d. lateral view of flower buds and staminate flower; e. pistillate flower; f. fruit; g. inflorescence; h. infruc- tescence. — Photos by Ren-Yong Yu.