Dendrobium discolor

Dendrobium discolor Lindl., Edwards's Bot. Reg. (1841) t. 52 Misc. 21.

Type: Loddiges cult. s.n. (Java) (holo K-LINDL).

An epiphytic or lithophytic herb. Stems up to 5 m tall, 1-5 cm diam., clustered on a short rhizome, swollen at base and dilated somewhat in middle. Leaves distichous, elliptic, ovate-elliptic, obtuse at obscurely bilobed apex, 5-20 by 2.8-8 cm; basal sheaths 3-5 cm long. Inflorescences 1-6 from apical nodes, 20-60 cm long, rather densely 20-80-flowered; bracts lanceolate, acuminate, 8-17 mm long, papery. Flowers with very convoluted and crisped segments; pedicel and ovary 2-3.5 cm long. Dorsal sepal linear-oblong, obtuse, 1.5-4 by 0.3-0.6 cm, recurved and twisted, strongly undulate on margins; lateral sepals oblong-lanceolate, subacute, 2.5-4 by 0.8-1.2 cm, recurved, margins markedly undulate; mentum shortly conical, 8-1.2 mm long. Petals suberect, spathulate or oblanceolate, obtuse to acute, 2-5 by 0.4-0.8 cm, twisted once to three times, with undulate margins. Lip 3-lobed, 1.5-2.5 by 0.8-1.5 cm; side-lobes obovate to oblong, rounded in front, erose on margins; midlobe small, triangular to ovate, acute, recurved and often twisted to one side; callus of 5 ridges slightly dilated at apex on basal half of midlobe. Column 3-6 mm long.
(after Cribb, 1986).

Colours: Stems brown, sometimes striped purple. Flowers creamy, yellow or brown, suffused with brown, bronze or even violet, lip with purple veins and a whitish callus.

Habitat: Epiphytic in tall trees and lithophytic in exposed positions. Inhabits areas with a strong seasonal climate. Altitude 0-550 m.

Flowering time in the wild: Mainly during the dry season (April-November).

Distribution: NE Australia (Queensland) and S New Guinea.

Distribution in New Guinea: Papua (Merauke region); Papua New Guinea (along the south coast from Western Province to Milne Bay).

Map: DISCOMAP.JPG [Dendrobium discolor Lindl., distribution map, redrawn from P. Cribb, Kew Bull. 41 (1986) 644, map 4, with new records added.]

Notes: Dendrobium discolor is a distinctive orchid only likely to be confused with Dendrobium conanthum, which also often has a rather convoluted flower. From the latter, it can be readily distinguished by its long-acuminate bracts and flowers in which the sepals and petals usually have undulate-crisped margins and the lip a five-ridged callus, a very small midlobe with upcurved sides and side lobes which are usually incurved and not rugulose on the upper surface.

The name Dendrobium undulatum has persisted in horticulture for this species and appears frequently as a parental name in Sander's List of Orchid Hybrids.

Dendrobium discolor is a very variable plant in nature particularly in its overall size and flower shape, size and colour. Several varieties have been formally recognised by various authors. The best known of these is var. broomfieldii (Fitzg.) M.A.Clem. & D.L.Jones, which is distinguished by its pure canary-yellow flowers which often have an enamel-like quality. This is informally known as 'Bensbach Yellow,' whereas the common form is locally called 'Moresby Gold.'.

Ferdinand von Mueller (1875) described var. albertisiana from New Guinea based on a collection by D'Albertis from the Fly River. It purportedly has a larger flower than the typical variety with markedly less undulate sepals and petals, a remote-cordate midlobe to the lip and the mid-ridge of the callus terminating in a distinct pointed tooth. Var. gracile also from New Guinea was described by J.J. Smith, who provided an illustration but cited no type specimen. It differs in having large flowers with narrow segments, retrorse but not recurved sepals, a narrow mentum and distinct callus ridge. The type of Dendrobium arachnanthe agrees well with this variety.

The variation in Dendrobium discolor seems more or less continuous rather than disjunct and it is probable that the recognition of so many distinct varieties is unwarranted. However, according to O'Byrne (1994) the entity that is popularly known as 'Rigo Twist' may deserve recognition as a variety or even as a distinct species.
(largely after Cribb, 1986).

Cultivation: Warm growing epiphyte, requires strong light and a dry resting period.