Dipodium, commonly known as hyacinth orchids, is a genus of approximately forty species in the family Orchidaceae (order Asparagales). The genus was formally described in 1810 by Scottish botanist Robert Brown in his Prodromus Florae Novae Hollandiae et Insulae Van Diemen, and it remains the sole genus of its alliance, Dipodium.
Members of the genus are perennial terrestrial herbs, climbers, or epiphytes distributed across tropical, subtropical, and temperate regions of south-east Asia, New Guinea, the Pacific Islands, and Australia. Eleven species are endemic to Australia. A distinctive feature of the genus is the prevalence of leafless mycoheterotrophic species, particularly in eastern Australia — plants that obtain nutrients entirely through a parasitic relationship with soil fungi rather than through photosynthesis. Other members bear medium-sized to very large, parallel-veined leaves with entire margins.
The flowers are among the most striking in the orchid family: large, often fragrant blooms arranged in a raceme of up to fifty flowers per stem. They range in colour from white and pink to purple, yellow, and green, frequently marked with spots or blotches. The sepals and petals are free and similar to each other, while the three-lobed labellum bears a distinctive central band of colourful hairs. Each flower carries two pollinia supported on two stipes — the structural feature that gives the genus its name, from the Greek di (two) and podia (little feet). After flowering, dehiscent capsules release between 30 and 500 seeds each, splitting longitudinally along six seams.
The genus is thought to attract native bees and wasps through floral mimicry. Traditional uses have been recorded in Bougainville, where an infusion of the leaves of Dipodium pandanum is drunk to relieve respiratory infections.
Etymology
The genus name Dipodium derives from the Greek di (two) and podia (little feet), a reference to the two stipes that support the pollinia in each flower. The genus was formally described in 1810 by Scottish botanist Robert Brown in Prodromus Florae Novae Hollandiae et Insulae Van Diemen. The common name "hyacinth orchids" alludes to the tall, showy flower spikes characteristic of the group.
Distribution
Hyacinth orchids are native to tropical, subtropical, and temperate regions of south-east Asia (Malaysia, the Philippines, Indonesia), New Guinea, and the Pacific Islands (Solomon Islands, Vanuatu, New Caledonia), with the greatest diversity in Australia, where eleven species are endemic. Within Australia they occur across a range of habitats from coastal lowlands to inland ranges and tablelands.
Ecology
Many species of Dipodium, particularly those in eastern Australia, are leafless mycoheterotrophs that lack chlorophyll and obtain all nutrients through associations with soil fungi rather than through photosynthesis. The flowers of leafed species are thought to attract pollinating native bees and wasps through floral mimicry, offering no reward in return.
Cultural Uses
An infusion made from the leaves of Dipodium pandanum is traditionally consumed in Bougainville (Papua New Guinea) as a remedy for respiratory infections.
