Trigonostemon villosus var. borneensis, (Merr.) Airy Shaw

Yu, R. - Y. & Welzen, P. C. van, 2018, A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia, Blumea 62 (3), pp. 179-229 : 220

b. var. borneensis (Merr.) Airy Shaw — Fig. 16 ; Map 12

Trigonostemon villosus Hook.f. var. borneensis (Merr.) Airy Shaw (1975) 205. — Trigonostemon borneensis Merr. (1929) 162; Jabl. (1963) 162; Whitmore (1973) 136. — Type: Elmer 20742 (holo PNH†; iso A, BISH*, BM, BR*, CAS*, CM*, G*, GH*, HBG*, K, L, M*, MICH*, NY*, P*, PH *, S*, SING, U, UC*), Borneo, near Tawao.

Trigonostemon hirsutus C.B.Rob. (1911) 335; Pax & K.Hoffm. (1914) 406; Merr.(1923) 451; Airy Shaw (1983b) 47; R.I. Milne (1995a) 28,in key,30, in key, 41, f. 3. — Type: BS (Robinson) 11798 (holo PNH†, not seen), Philippines, Mindanao, Zamboanga District, Port Banga (synonymy somewhat doubtful as the type is lost).

Trigonostemon wenzelii Merr. (1913) 380; Pax & K.Hoffm. (1919) 41; Merr. (1923) 453. — Type: Wenzel 186 (holo PNH†; iso A*, G*, GH*, L, US*), Philippines, Leyte, Dagami .

Trigonostemon villosus Hook.f. var. caesius R.I. Milne (1995a) 28, in key, 30, in key, 37. — Type: SAN (Ampuria) 40236 (holo K; iso SAN ), Sabah, Beaufort District, Beaufort Hill.

Leaves: petioles 0.5–5.5 cm long; blade elliptic to obovate, 5.5–18 by 2.5–6.5 cm, glabrous above, often pubescent beneath. Inflorescences unisexual, up to 16 cm long, staminate ones racemose or thyrsoid, sometimes cauliflorous, a few flowers per node, never clustered as glomerules; pistillate ones racemose, often fewer than 4 flowers present at one time. Staminate flowers: sepals pink, often with a showy gland near the apex outside; petals obovate, with an orange to yellowish flame-like honey mark near the base. Pistillate flowers: sepals elliptic, margin entire; ovary villose. Fruits green when young, red when mature, glabrous to pubescent.

Distribution — Sumatra, Borneo (Sabah), Philippines.

Habitat & Ecology — Primary lowland rainforests, often on hillsides or near rivers, growing on well-drained brown loam soil. Flowering: June to December; fruiting: July to December.

Note — Some collections from Sumatra (e.g., W. J. J. O de Wilde & B. E. E de Wilde -Duyfjes 19367, 21244, 21362) display an intermediate form between the variety villosus and variety borneensis . They have short petioles (shorter than 2.5 cm), seemingly unisexual inflorescences and often 1 or 2 pistillate flowers per inflorescence at one time, which all show clear allegiance to var. borneensis . Because of this, they are tentatively placed under var. borneensis even though there is a huge gap between their main distribution locations (Sumatra, Sabah), but the serrate sepals of the pistillate flowers with an acuminate apex do somewhat resemble var. villosus .

Figures

Fig. 16 Trigonostemon villosus Hook.f.var.villosus (a, c, f), Forest Research Institute Malaysia,Kepong, Malay Peninsula and Trigonostemon villosus Hook.f. var. borneensis (Merr.) Airy Shaw (b, d, e, g–m), Segaliud Lokan Forest Reserve, Sabah, Malaysia. a, b. Growing habit; c, d. top view of the tree; e. bark and reddish exude; f, g. pistillate inflorescence; h, i. staminate flower; j, k. pistillate flower; l, m. fruit. — Photos by Ren-Yong Yu.