Underground orchid  (Rhizanthella gardneri)

Classified as Vulnerable on the 1997 IUCN Red List of Threatened Plants (1), and listed on Appendix II of CITES (3).

These highly enigmatic orchids spend all of their life below the ground; even the flowering head does not break the surface of the soil (4). The plant consists of a fleshy underground storage stem (or tuber), which produces a flower head consisting of around 150 tightly packed, tiny flowers (5). When first discovered in 1928, these extraordinary orchids generated such excitement that a wax model was toured around the British Isles (4).

Endemic to Western Australia, six populations are currently known; these are found in the central wheatbelt near to the town of Corrigin and from locations close to the south coast (5).

Rhizanthella gardneri requires the root system of the broom honey myrtle (Melaleuca uncinata) in order to grow, and is always found growing in association with this species (5).

These orchids reproduce vegetatively to produce up to three daughter stems. It also undergoes sexual reproduction, and underground insects such as termites and gnats are known to pollinate the flowers (5). The resultant fruit may take up to six months to mature; in all studied flowers these were not dispersed and eventually decayed, thus releasing their seeds (5). It may be, however, that native marsupials were important dispersal agents (5). This orchid is always found in association with the root system of broom honey myrtle (Melaleuca uncinata), obtaining nutrients from these plants by way of a mycorrhizal fungus (4).

Large areas of bushland have been developed for agriculture in much of southern Western Australia, and it is likely that this loss of habitat is one of the main causes of the small population of Rhizanthella gardneri today (5). Further threats to habitat include drought, the encroachment of salt and a decline in health of the 'host' plant (4). Remaining populations of the underground orchid are isolated in the fragments of habitat that persist today (5).

Three of the known populations of Rhizanthella gardneri are protected within Nature Reserves (5), and a concerted initiative has been launched to safeguard this species for future generations (4). A partnership between the Millennium Seed Bank of the Royal Botanic Gardens, Kew (6), Australia's Endangered Species Program and Perth's Kings Park and Botanic Gardens are undertaking DNA fingerprinting and seed-banking of this rare orchid in an attempt to establish a captive breeding programme (4).

To find out more about plant conservation see:

• Royal Botanic Gardens, Kew - Millennium Seed Bank Project:
  http://www.kew.org/msbp/index.htm