Trigonostemon balgooyi R.Y.Yu & Welzen, 2018

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 188-189

3. Trigonostemon balgooyi R.Y.Yu & Welzen , sp. nov. — Fig. 2 ; Map 3

This species strongly resembles T. merrillii and T. villosus , but differs by its appressed stellately bundled hairs, cordate bracts subtending the pistillate flowers and staminate flowers with 5 instead of 3 stamens. — Type: M. M. J. van Balgooy 7102 (holo L; iso K, KEP , SAN ), Malaysia, Johor,Endau-Rompin, Kuala Jasin, N2°32' E103°22'. Paratypes: Sinclair 10598 (K, SING; E, NY not seen), Malaysia, Johor, Gunung Panti, Waterfall, Lombong; KEP FRI (Kamarul Hisham et al.) 73820 (K, KEP , SAN,SING ;BKF not seen), Malaysia, Johor, Endau-Rompin S.P., Bagoh camp area; KEP FRI (Kamarul Hisham et al.) 73826 ( KEP ), Malaysia, Johor, Mersing, Endau-Rompin S.P., trail to Kuala Kembah camp from Bagoh; Stone 8719 (KLU), Malaysia, Johor, Kota Tinggi, Ayer Terjun.

Shrubs or small trees, 2–3 m tall, dbh 1.5–3 cm; flowering branches 3–4 mm diam. Indumentum consisting of 2 layers of hairs (except on sepals and upper surface of leaves and bracts, these glabrous or with only 1 layer of hairs), upper layer hispid, with simple long and rigid golden hairs, lower layer of stellately bundled hairs consisting of 3–5 tiny, appressed, whitish hairs originating from one papillose point. Outer bark c. 0.1 mm thick, dark brownish to greyish, hairy, often slightly fissured; inner bark 0.1–0.2 mm thick, whitish to reddish to brownish, often with sap (solidified when dry); wood creamy, reddish brown. Stipules subulate, c. 0.5 mm long, caducous. Leaves: petiole terete, 1.5–6 cm long, 1–1.5 mm diam, hairy; blade oblong to oblanceolate, 12–23 by 1.5–6 cm, chartaceous, base cuneate to acute, with 2 nipple-like glands adaxially, margin distantly serrate, teeth small, falcate, apex acuminate to caudate, upper surface medium green, slightly bullate, papillose hispid (no stellate hairs), lower surface pale green, papillose hispid and with stellately bundled hairs on venation; venation penninerved, midrib slightly elevated above and distinctly elevated beneath, nerves 9 –11 pairs, curved and bow-shaped, narrowed and connected along margin, veins reticulate, often obscure above. Inflorescences: staminate ones pyramidal paniculate or racemose, sometime cauliflorous, rachis at least up to 9 cm long, c. 1 mm diam (lower part), hispid and with stellately bundled hairs; bracts lanceolate, up to 7.5 by 1.3 mm, sparsely papillose hispid above, hispid and with stellately bundled hairs beneath; pistillate ones often single-flowered, peduncles 4–6 cm long, c. 0.6 mm diam (evenly wide throughout), sparsely hispid; bracts in lower part often 1.3–1.8 by 0.4–0.5 cm, hispid and with sparse stellately bundled hairs; bracts subtending the pistillate flower cordate, 1.5–2.1 by 0.6–1.2 cm, palmately veined, sparsely hispid above and hispid and with sparse stellately bundled hairs (often along veins) beneath. Staminate flowers c. 7 mm diam; pedicel indiscernible; sepals elliptic, 1–1.5 by c. 1 mm, pale green, sparsely papillose hispid outside, glabrous inside; petals elliptic, c. 3.3 by 2.5 mm, red to maroon, both sides glabrous, sometimes with a few pustules; disc lobes glandular, 0.25–0.3 by 0.3–0.6 mm, deep purple, apex rounded, slightly recurved; stamens 5, androphore c. 0.7 mm long, 5-cleft at apex; anthers ellipsoid, each theca 0.5–0.6 mm long, connectives apically with dark purplish droplets (or expanded cells) with secretion. Pistillate flowers c. 1.2 mm diam; pedicel less than 5 mm long; sepals triangular, c. 6.5 by 4.5 mm, apex acuminate, hispid outside, sparsely hispid and with sparse stellately bundled hairs (often along veins) inside; petals orbicular, 6–7 by 5–6.8 mm, maroon; disc not seen; ovary c. 1.2 mm diam, sparsely hairy; style c. 0.2 mm long, stigmas deeply divided, free parts c. 1.5 mm long. Fruits: sepals (remnants) persistent, 1.3–1.5 by 0.55–1 mm, with sparse stellately bundled hairs outside, glabrous inside; columella 5.5–7 mm long; cocci white, with a few hairs when young and nearly glabrous when mature; wall c. 0.65 mm thick, exocarp not detaching. Seeds c. 6 mm diam, brown when dry.

Distribution — Malay Peninsula (endemic).

Habitat & Ecology — Lowland primary (dipterocarp) rainforest on clay soil on hillside or riverside. Flowering: March to April, July; fruiting: July.

Note — The only species in Malesia that has stellately bundled hairs, which makes it quite unique ( T. reidioides in Thailand and Indochina also has stellately bundled hairs). The cordate bracts of the pistillate flowers are also distinct. The pistillate disc was not seen because it was covered by petals in the only flower present on the available material.

Figures

Fig. 2 Trigonostemon balgooyi R.Y.Yu & Welzen. a. Flowering branch; b. leaf base with adaxial glands; c. part of inflorescence; d. staminate flower (sepals and petal removed); e. anthers, front and lateral views (all: Van Balgooy 7102, L). — Drawing by Esmée Winkel, 2016.