Tropical hyacinth-orchid

Description

Dipodium stenocheilum, commonly known as tropical hyacinth-orchid, is a leafless saprophytic orchid that is endemic to northern Australia. For most of the year the plant is dormant but in summer it produces a tall flowering stem with up to twenty five white flowers with purple spots and a mauve labellum. Dipodium stenocheilum is a leafless, tuberous, perennial, mycoheterotrophic herb. For most of the year the plant is dormant but in summer it produces between three and twenty five white flowers with purple spots and 40–50 mm (1.6–2.0 in) wide are borne on a greenish yellow flowering stem 40–120 cm (20–50 in) tall. The dorsal sepal is 20–30 mm (0.8–1 in) long, 4–6 mm (0.16–0.24 in) wide but the lateral sepals are slightly longer, the petals shorter than both. The sepals and petals are free from each other and flat or only slightly curved backwards. The labellum is mauve with darker markings, 15–20 mm (0.6–0.8 in) long, 5–7 mm (0.2–0.3 in) wide and has three lobes with a central band of mauve hairs. Flowering occurs from November to March. Dipodium stenocheilum was first formally described in 1927 by Otto Schwarz and the description was published in Repertorium Specierum Novarum Regni Vegetabilis. The type specimen was collected near Port Darwin. The specific epithet (stenocheilum) is derived from the Ancient Greek words stenos meaning "narrow" or "tight": 546  and cheilos meaning "lip" or "rim". Dipodium stenocheilum occurs in the Northern Territory including Melville Island, on the Cape York Peninsula and the Kimberley region of Western Australia. Pollination of this species, as for all species in the genus, is by native bees and wasps. Andrew Phillip Brown, Matthew David Barrett and others have suggested that collections from Western Australia represent two species, yet to be formally described. They are the sandstone hyacinth orchid D. ammolithum (also known as Dipodium sp. 'sandstone') and the basalt hyacinth orchid D. basalticum (also known as Dipodium sp. 'basalt woodland'). No leafless species of Dipodium has been successfully maintained in cultivation due to the inability to replicate the association with mycorrhizal fungi in a horticultural context. Hyacinth orchids are found in Malaysia, the Philippines, Indonesia, the Solomon Islands, the New Hebrides, New Caledonia, New Guinea and Australia where eleven species are endemic. They occur in a range of habitats from coastal lowlands to ranges and tablelands.