Dendrobium is a large genus with around 1400 species spread throughout Asia and the Pacific. Australia has about 56 species, many of which are cultivated. Considerable hybridization has been carried out within the genus to produce improved horticultural forms and a number of naturally occurring hybrids are also in cultivation.
Major taxonomic revision of the Dendrobium group has occurred in recent years with many species being transferred to new genera. Some of these changes have been reasonably widely accepted (eg Dockrillia) while the status of others is less certain. The various forms of Dendrobium speciosum have been transferred to the genus Thelychiton by some authorities but the earlier name is retained here in accordance with the Australian Plant Census.
Dendrobium speciosum is a lithophyte (growing on rocks) or an epiphyte (growing on another living plant, but not parasitic in nature). Pseudobulbs are up to 45 cm long, erect or spreading, thickest near base and often tapering towards the apex. There are usually 2 to 5 thick leaves at the top of each pseudobulb. Flowers occur on long stems in large clusters which may consist of over 100 flowers per stem. They are usually pure white to creamy yellow with purple dots on the labellum. Flowers are seen from late winter to spring.
There are a number of different form and varieties of Dendrobium speciosum which will become new species under the taxonomic revision. The most commonly encountered are D.speciosum var.speciosum and D.speciosum var.hillii. The later is now regarded as Dendrobium tarberi by many authorities and differs from D.speciosum var.speciosum in having longer, untapered pseudobulbs and is more commonly found growing on trees.
D.speciosum is popular in cultivation and is easy to grow in tropical to temperate climates. It can be grown on branches of trees or on rocks where it receives nutrients through the break down of leaf litter that accumulates around its root system. While the plant is establishing its root system, it may need to be fixed into position by wire or twine. Eventually new roots will form which will grip the substrate firmly. The plant should not be planted directly into soil as the root system is not adapted to constant moisture. It can also be grown as a container plant in a coarse medium such as pinebark chips but it may require frequent re-potting. Glasshouse cultivation is not necessary. It should not be grown in dense shade or flowering will be discouraged. Application of liquid fertilizer during the growing season (spring – summer) will promote healthy growth. Watering should be kept to a minimum during winter.
Plants can usually be obtained through specialist Australian orchid nurseries. The plant can be propagated by division of the clump but propagation by seed requires specialist treatment which is not really practical except for true orchid enthusiasts.
Photo: Brian Walters
Photo: Brian Walters