Dendrobium

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 : 201-202

Dendrobium sect. Formosae (Benth. & Hook.f.) Hook.f.

Flora of British India 5: 710 (1890). — Dendrobium grex Formosae Benth. & Hook.f., Genera Plantarum 3: 500 (1883). — Dendrobium subsect. Nigrohirsutae Lindl., The Journal of the Linnean Society of London, Botany 3: 16 (1859). — Dendrobium subgen. Nigrohirsutae (Lindl.) Kraenzl., Das Pflanzenreich : regni vegetabilis conspectus 45: 85 (1910). — Dendrobium subgen. Oxygenianthe Schltr., Repertorium specierum novarum regni vegetabilis 1: 448 (1912).

LECTOTYPUS. — D. formosum Roxb. ex Lindl.

STUDIED SPECIES

The section includes 50-55species occurring in mainland tropical and subtropical SE Asia, Indonesia and the Philippines, 19 species occur in studied area.

DESCRIPTION

Epiphytic or rarely lithophytic plants, hairy with black, dark brownish or white hairs. Stems erect or ascending, simple, usually slightly flexuose, yellow-green to yellow when dry, fleshy, cylindric, fusiform or clavate usually many tufted together. Leaves, distichous, leathery, base decurrent forming clasping sheaths, usually unequally bilobulate at apex. Inflorescences 1-5, subterminal, short, usually less than 1 cm long, with 1-5 flowers; floral bracts small, ovate. Pedicel and ovary greenish to white, glabrous. Flowers usually large and showy, white, yellowish or light greenish, thickly textured, 2-3 month lasting; sepals and petals subsimilar, or petals wider; mentum distinct, broad to narrow, spur-like; lip 3-lobed, trumpet shaped, white, yellow or red; disc rugose, often with ciliate or fringed ridges. Column stout, broad and short, with 2 short conical stelidia at apex; anther cap broadly conic to hemispheric, papillose or hairy along front margin.Capsules large, nutant, fusiform to obovoid. All species of this section including those that occurs in eastern Indochina have attractive, long-lasting flowers and are of outstanding significance for ornamental horticulture and breeding. Being extensively collected in nature for the trade, they have become endangered and even completely extinct in many areas of their primary distribution.

KEY TO SPECIES DENDROBIUM SECT. FORMOSAE (BENTH. & HOOK.F.) HOOK.F.

1. Sepals and petals pure white or light pale yellowish ..................................................................................... 2

— Sepals and petals bright yellow .................................................................................................................. 18

2. Mentum saccate, almost half-globular ......................................................................................................... 3 — Mentum conic to cylindric, spur-like .......................................................................................................... 6

3. Median lobe of lip emarginate-retuse or shallowly two-lobed ...................................................................... 4 — Median lobe triangular or rounded at apex .................................................................................................. 5

4. Stem 2-7 cm long, usually shorter than 5 cm, broadly clavate, obovoid to almost globular, of 2-5 internodes; flowers 2.5-3 cm across; sepals and petals 1.5-2 cm long; lip 2-2.6 cm long, 1.2-1.6 cm wide; epichile entirely yellow or red, strongly recurved, with tip decurved or reflexed ..................................... 1. D. bellatulum Rolfe

— Stem 5-25 cm long, fusiform to cylindrical of few to many internodes; flowers 4-7 cm across; sepals and petals 2.2-3.5 cm long; lip 3-5.5 cm long, 2.5-3.2 cm wide; epichile white, yellow or red at base, straight or only slightly recurved ..................................................................................................... 2. D. christyanum Rchb. f.

5. Flowers fragrant, 1.8-2.4 cm across; sepals and petals 1-1.2 cm long; petals ovate, as broad as median sepal; lip 1.5- 2 cm long, 1.4-1.6 cm wide, white, side lobes light pale green, disc light yellow ............. 3. D. scabrilingue Lindl.

— Flowers odorless, 4-6 cm across; sepals and petals 3-4 cm long; petals and sepals subsimilar triangular ovate; lip 3.2- 2.6 cm long, 2.6-2.8 cm wide, side lobes and disc bright red, margin of epichile white ..... 4. D. suzukii T.Yukawa

6. Epichile as broad as or broader than flattened hypochile .............................................................................. 7 — Epichile narrower than flattened hypochile .................................................................................................. 9

7. Epichile with triangular acute apex ............................................................................... 5. D. draconis Rchb. f. — Epichile with semi-orbicular retuse apex ...................................................................................................... 8

8. Lip 2.5-4 cm long; disc pink to red, with 5 low insignificant rugose keels; flowers odorless ............................ ............................................................................................................................... 6. D. kontumense Gagnep. — Lip 4-5 cm long; disc red-orange to orange-yellow, thick, verruculose, without distinct keels; flowers sweet fragrant .................................................................................. 7. D. roseiodorum Sathap., T.Yukawa & Seelanan

9. Petals much broader than sepals; sepals and petals of rather thin texture; lip disc thin, with thin keels or almost flat ............................................................................................................................................................ 10

— Petals as wide as sepals or narrower, rarely a little wider than sepals; sepals and petals coriaceous, glossy; lip disc thick, often finely rugose with thick keels .................................................................................................. 13

10. Lip deeply 3-lobed, entirely bright yellow-orange; lip side lobes triangular, acute; median lobe lanceolate rhomboid, acute, with thick fleshy verruculose band; disc with erect retrorse, emarginate-globose callus ................ ...................................................................................................... 8. D. daklakense Tich, Schuit. & J.J.Verm.

— Lip shallowly or indistinctly 3-lobed, white yellow, orange or red marks only on disc and side lobes; lip lateral lobes semicircular, obovate or indistinctly rectangular, more or less rounded at apex; median lobe almost flat, emarginate or rounded and shortly apiculate; disc with low indistinct parallel keels extending from base of lip to base of median lobe ............................................................................................................................... 11

11. Flowers 6-9 cm across; sepals 3-4 cm long; flattened lip 3.3-4.5 cm wide; median lobe retuse, with rather deep

sinus at apex; disc with flat broad fleshy keel splitting distally into 3-5 low parallel lamellas ...........................

............................................................................................................................... 9. D. infundibulum Lindl. — Flowers 3-5 cm across; sepals 2.5-3 cm long; flattened lip 2.5-3.2 cm wide; median lobe orbiculate, shortly apiculate;

disc with 3-11 low indistinct parallel keels extending from base of lip to base of median lobe ......................... 12

12. Disc yellow to yellow-orange, with 3-4(5) low keels; side lobes pure white or with yellow marks along nerves, median lobe obovate to rectangular, narrowing to base, irregularly denticulate and undulate along margin .... ........................................................................................................................10. D. wattii (Hook.f.) Rchb.f.

— Disc bright red, with 7-13 low keels; side lobes white with bright red stripes along inflated, keel-like nerves, median lobe semi-orbicular to broadly ovate, broadening to the base, almost entire and flat ........................... ............................................................................................................................... 11. D. multilineatum Kerr

13. Lateral sepals and ovary with distinct dorsal keels; disc of lip fimbriate or ciliate ........................................ 14 — Lateral sepals and ovary without distinct keels; disc of lip naked, papillose or sparsely setose ..................... 15

14. Lip ciliate along veins, without distinct keels or with low insignificant ciliate keels; keels on back of sepals hardly continuing down the ovary ....................................................................... 12. D. williamsonii Day & Rchb. f.

— Lip with 5-7 fat, densely fimbriate keels extending to the median lobe; keels on back of sepals continuing down the terete ovary and pedicel ................................................................................... 13. D. cariniferum Rchb. f.

15. Flowers not widely opening, campanulate, 1.5-2.5(3) cm across, nodding, sepals and petals straight; lip broadly obovate rhombic, entire or 3-lobed, denticulate or irregularly fringed along apex; median lobe (in 3-lobed lip) ovate, 3 time smaller than side lobes; veins on the lip fanning out from base; stems usually less than 30 cm long ...... 16

— Flowers widely opening, (3) 3.5-5 cm across, sepals and petals sometime more or less recurved, horizontally directed or suberect; lip pandurate, 3-lobe or broadly ovate indistinctly 3-lobed, entire and undulate along margin; median lobe as large as side lobes or larger; veins on the lip more or less parallel; stems usually longer than 30 cm ....... 17

16. Stems slender, reed-like, 3–5 mm in diameter; flowers 2-3 cm across, sepals 1.5–2.2 cm long, mentum as long as pedicel and ovary or longer; lip apex entire to indistinctly 3-lobed, irregularly dentate or fringed; disc naked or sparsely setose along veins .................................................................................... 14. D. longicornu Lindl.

— Stems rather stout, fleshy, 0.5-1 cm in diam; flowers 1.5-2 cm across; sepals 1.4-1.6 cm long; mentum shorter than pedicel and ovary; lip apex distinctly 3-lobed, median lobe triangular ovate, irregularly denticulate; disc naked .......................................................................................................................... 15. D. chapaense Aver.

17. Flowers light yellowish to almost white, lip with numerous bright red veins contrasting with pale background; petals triangular narrowly ovate, acuminate, 2.2-3 cm long, 6-10 mm wide, as wide as sepals, commonly recurved and irregularly undulate along margin; lip pandurate, distinctly 3-lobed; 2.2-3 cm long, 1.6-2.2 cm wide, median lobe as large as side lobes, strongly undulate along margin, often emarginate; disc with 4 indistinct, low keels .................................................................................................................... 16. D. ochraceum De Wild.

— Flowers white; disc uniformly bright red; petals obovate, acute to round at apex, 2.8-3.4 cm long 1.2-1.4 cm wide, broader than sepals, flat and straight; lip obovate, indistinctly 3-lobed, 3-3.5 cm long, 2-2.5 cm wide, median lobe much smaller than side lobes, finely undulate along margin, shortly apiculate; disc with longitudinal lamella splitting distally on medial lobe into 3-5 low keels .................... 17. D. trankimianum T.Yukawa

18. Indumentum hairs white, long; stem 0.5-1 cm in diameter; flowers 2.5-3 cm across; tepals less than 2.4 cm long; sepals not much keeled at back ................................................................. 18. D. senile E.C.Parish & Rchb. f.

— Indumentum hairs dark brown to black, very short; stem 1.2-1.8 cm in diameter; flowers 3-4 cm across; tepals 2.5 cm long; sepals at back with strong keels continuing down the ovary ................ 19. D. trigonopus Rchb. f.