Trigonostemon tuberculatus F.Du & Ju He

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 43-44

27. Trigonostemon tuberculatus F.Du & Ju He — sect. Tylosepalum — Map 3

Trigonostemon tuberculatus F.Du & Ju He in Du et al. (2010) 111, f. 1, 2. — Type: Du, He & Zhang 200401 (holo SWFC, not seen), China, Yunnan, Yuanjiang .

Shrubs, up to 2 m tall; flowering branches 2.3–2.5 mm diam, densely pubescent. Bark 0.1–0.2 mm thick, pale brown; wood yellow to brown. Stipules subulate, 0.5–0.7 mm long, caducous, densely pubescent at base, often buried in hairs. Leaves: petiole terete, 1.4–3.3 cm long, 0.8–1 mm diam, densely pubescent; blade ovate, 4.4–6.9 by 1.6–4.7 cm, coriaceous, base acute to truncate, 2 adaxial glands present, margin distantly serrate, teeth glandular, apex acute, both surfaces densely pubescent; venation often palmate, densely pubescent on both sides; midrib and basal secondary veins slightly elevated on both surfaces, other secondary veins 5–7 pairs, bifurcate and con- nected along margin, tertiary veins scalariform, obscure, veinlets reticulate, obscure. Inflorescences seemingly unisexual, axillary or terminal panicles; main axis terete, 2.7–5 cm long, 0.5–1 mm diam, densely pubescent; bracts lanceolate, 0.8–1.8 by 0.5–0.8 mm, densely pubescent. Staminate flowers 4.1–6.1 mm diam; pedicel 1.6–2.7 mm long, 0.3–0.5 mm diam, densely pubescent; sepals elliptic, 1.5–3 by 0.9–1.5 mm, base connate, margin entire, apex acute, pubescent outside; petals spathu- late, 3–3.8 by 1.4–2 mm, apex rounded, yellow, glabrous; disc annular, c. 0.4 mm wide, pubescent; stamens 3, androphore 0.9–1 mm long, 0.15–0.2 mm diam, anthers ellipsoid, 0.6–0.7 mm long. Pistillate flowers ( Du et al. 2010): sepals elliptic, c. 3 mm long, with buff vesicles, densely tomentose outside; petals narrowly elliptic, c. 4 mm long, glabrous, with or without 1–2 dichotomous glands; disc unknown; ovary tuberculate, densely long tomentose, stigmas bifid at apex. Fruits ( Du et al. 2010) oblate, c. 3 cm diam, green when young, warts 1–2 mm diam. Seeds ( Du et al. 2010) flat, elliptic, 0.9–1 cm long, c. 0.6 mm diam; aril c. 1 mm thick, spongy, green.

Distribution — China (Yuanjiang, Yunnan; endemic).

Habitat & Ecology — On hill slopes, on the banks of the Yuanjiang river, in arid areas. Elevation: c. 300 m. Flowering: March.

Notes — 1. The species has a few very unusual characters: it is the only species known to have a pubescent disc; the fruits are very warty and exceptionally large; the seeds have a green aril ( Du et al. 2010).

2. We have only seen one collection of the species; the description of pistillate flowers, fruits and seeds is based on Du et al. 2010. The colour of the staminate petals (yellow) was known from photos by Si-Yu Zhang posted on Plant Photo Bank of China (http://ppbc.iplant.cn/).

Figures

Map 3 Distribution of Trigonostemon bonianus Gagnep.(X), T. lanceolatus (S.Moore) Pax (▲), T. pachyphyllus Airy Shaw (★) and T. tuberculatus F.Du & Ju He (●).