Dendrobium trigonopus Rchb.

Averyanov, Leonid V., Ponert, Jan, Nguyen, Phi Tam, Duy, Nong Van, Khang, Nguyen Sinh & Nguyen, Van Canh, 2016, A survey of Dendrobium Sw. sect. Formosae (Benth. & Hook. f.) Hook. f. in Cambodia, Laos and Vietnam, Adansonia 38 (2), pp. 199-217 : 216-217

19. Dendrobium trigonopus Rchb. f.

The Gardeners’ Chronicle, ser. 3, 2: 682 (1887). — Gagnep., Flore générale de l’Indo-Chine 6 (2): 238 (1933). — Seidenf., Opera Botanica 83: 109, fig. 65, table 14c (1985); 114: 210 (1992). — Newman et al., A Checklist for the Vascular Plants of Lao: 265 (2007). — Schuiteman et al., Nordic Journal of Botany 26: 288 (2008). — Zhu Guanghua et al., Flora of China 25: 391 (2009). — Aver., Turczaninowia 8 (1): 62, table 1e (2005).

TYPUS. — Myanmar. Birmah, Messrs. Hugh Low & Co., IV.1887

(type location unknown). HABITAT, PHENOLOGY AND CONSERVATION STATUS. — Epiphyte

on tall trees in primary evergreen broad-leaved forest on granite, shale and rocky limestone, particularly on steep rocky slopes and on mountain tops. 800-1800 m. Fl. (February) March-May, October. Rare. Expected IUCN Red List status – EN.

DISTRIBUTION. — Laos (Khammouan, Vientiane), Vietnam (Dien Bien, Lam Dong, Son La). Myanmar , S. China , N. Thailand .

MATERIAL EXAMINED. — Laos. Khammouan, M.Newman et al., s.n. ( NUOL cult. OL 645), B.Svengsuksa et al., s.n. ( NUOL cult. OL 1300, OL 821); Vientiane, A.D.Kerr 0330 ( K); Vientiane, N.Soulivong s.n., ( NUOL cult. OL 309); Vientiane, Phu Khao Khouai, Rendon 118 ( C), A.D.Kerr 2479, 2481 ( C); Xiangkhouang, Kham, Huad village, LA-VN 1095 ( FOF, HNL, LE).

Vietnam. Dien Bien, Na U, CPC 2427 ( LE, LE photo) ; Dien Bien, sine loc., L. Averyanov s.n., IV.2011 ( LE photo) ; Lam Dong, Dalat area , L.Averyanov s.n., anno 2004 ( LE photo) ; Lam Dong, Dalat area, L. Averyanov s.n., X.2005 ( LE photo) ; Son La prov., Son La city area, P. K. Loc P-10701 ( LE, LE photo) ; Son La, Son La city area, Chieng Co , CPC 1141 a ( LE, LE photo); NW Vietnam, sine loc., HAL 12851 K ( LE photo) .

DESCRIPTION

Stems fusiform to clavate, 5-15(20) cm, 1-1.8 cm in diameter, with (4)5-10 nodes. Leaves narrowly ovate to oblong lanceolate, 5-8(10) cm long, (1)1.5-2(2.5) cm wide. Inflorescences 1-3(4), each with 1-3 flowers; floral bracts ovate, acute, 4-8 mm long. Pedicel and ovary yellowish green, 2-5 cm long, ovary trigonous in section. Flowers sweet honey fragrant, slightly nodding, widely opening, 2.5-3.5(4) cm across, yellow, lip disc tinged with pale green. Sepals and petals subsimilar, triangular ovate, acute to shortly acuminate, (1.5)2-2.5(3) cm long, 0.7-1 cm wide; sepals dorsally keeled; petals little wider. Lip very rigid, densely verruculose, nearly parallel to column, denticulate along margin, shortly clawed, suborbicular, (1.5) 1.8-2.5 cm long and wide, 3-lobe; side lobes broadly obovate to obscurely quadrate, apex rounded to truncate; median lobe triangular to reniform, obtuse, orbicular to slightly emarginate. Mentum subglobose, 3-5 mm long and wide. Column pale yellow, 5-6 mm tall, anther cap conical, glabrous, 2-3 mm tall and wide ( Fig. 4I ).

REMARK

Records of this species for southern Vietnam (Lam Dong) are based on cultivated plants probably originated from Dalat City area. These records need confirmation by further field investigations. Molecular studies place this species outside of section Formosae ( Sathapattayanon 2008).

Figures

FIG. 4. — A-C, Dendrobium chapaense Aver. (25.XI.2015, L.Averyanov s.n.); D, E, D. ochraceum De Wild.; D, CPC 3576; E, HAL 8056; F, G, D. trankimianum T.Yukawa; F, Hon Giao, J.Ponert et al., s.n.; G, L.Averyanov s.n., 2005; H, D. senile E.C.Parish & Rchb.f. (L.Averyanov s.n., IV.2011); I, D. trigonopus Rchb.f. (CPC 1141a). Photos: A-E, G-I, L. Averyanov; F, J. Ponert.