Rhizanthella gardneri

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Western underground orchid
Rhizanthella gardneri — Fred Hort.jpg
Rhizanthella gardneri

Critically endangered (EPBC Act
)
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Orchidaceae
Subfamily: Orchidoideae
Tribe: Diurideae
Genus: Rhizanthella
Species:
R. gardneri
Binomial name
Rhizanthella gardneri
R.S.Rogers[1]

Rhizanthella gardneri, commonly known as western underground orchid,[2] is a species of flowering plant in the orchid family and is endemic to the southwest of Western Australia. It is a herb that spends its entire life cycle, including flowering, at or below the soil surface. A head of up to 100 small reddish to cream-coloured, inward facing flowers surrounded by large, cream-coloured bracts with a horizontal rhizome is produced between May and July.

Description

Rhizanthella gardneri is a leafless,

capsules of other orchids that produce minute, dust-like seeds dispersed by the wind, this species produces indehiscent fruit.[3][4][5]

Discovery, taxonomy and naming

John Trott discovered the first specimen of R. gardneri during ploughing operations in May 1928 on his farm near Corrigin. The discovery generated such excitement that a wax model was toured around the British Isles.[6] Specimens were found a further six times in similar circumstances between the Corrigin and Dowerin areas, until 1959. The next confirmed sighting was by John McGuiness near Munglinup in 1979, of plants in their natural habitat. In 1981 and 1982, surveys in the Munglinup area located more than one hundred flowering specimens.[2][4][5] The Munglinup population is now regarded as the separate species, Rhizanthella johnstonii.[7]

Rhizanthella gardneri was first formally described in 1928 by Richard Sanders Rogers in the Journal of the Royal Society of Western Australia from specimens collected near Corrigin in May of the same year.[8] The specific epithet (gardneri) honours Charles Gardner, assistant botanist to the Western Australian Government at that time.[9]

Distribution and habitat

Rhizanthella gardneri is only known from the

biogeographic region of Western Australia, where it grows in association with broom honeymyrtle (Melaleuca uncinata), between Corrigin and Babakin.[3][10][7]

Ecology

As with other orchids in the genus Rhizanthella, all parts of the life cycle of R. gardneri, including flowering, are subterranean. The orchid obtains its energy and nutrients as a

myco-heterotroph via mycorrhizal fungi that form associations with the roots of broombush species including M. uncinata, M. scalena and M. hamata.[6] The fungus involved is thought to be Thanatephorus gardneri.[11][12][13]

The flowers of R. gardneri are subterranean but the heads crack open the soil surface as they mature, and sometimes the tips of the bracts protrude through the leaf litter, leaving a small opening through which pollinators may enter. Termites and ants have been seen to enter the flower heads. The orchid's seeds are too large to be dispersed by the wind and it is possible that the succulent fruit is eaten by small mammals and the seeds passed out of their faeces.[2][4]

Conservation status

The species is classified as "critically endangered" under the Australian Government Environment Protection and Biodiversity Conservation Act 1999 and as "Threatened Flora (Declared Rare Flora — Extant)" by the Department of Environment and Conservation (Western Australia).[5][10]

Much of the central and southern Wheatbelt of Western Australia has been cleared for agriculture, or affected by drought, resulting in the loss of broombush habitat or a reduction in the level of bark and leaf litter necessary to protect the underground orchid and a reduction in the area suitable for translocation. The main threats to the species include lack of suitable habitat, degraded habitat, drought and rising soil salinity.[5]

Three of the known populations of Rhizanthella gardneri are protected within

Millennium Seed Bank of the Royal Botanic Gardens, Kew, 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 propagation programme.[6]

References

  1. ^ "Rhizanthella gardneri". Australian Plant Census. Retrieved 25 September 2019.
  2. ^
    ISBN 9780980348149
    .
  3. ^ a b c Hágsater, E. and Dumont, V. (1996) Orchids: Status Survey and Conservation Action Plan. IUCN/SSC Orchid Specialist Group, IUCN, Gland.
  4. ^
    ISBN 9780646562322
    .
  5. ^ a b c d Brown, Andrew; Batty, Andrew; Brundrett, Mark; Dixon, Kingsley. "Underground Orchid (Rhizanthella gardneri) - Interim Recovery Plant 2003–2008" (PDF). Australian Government Department of the Environment. Retrieved 26 September 2020.
  6. ^ a b c d Dixon, K. (2003). "Underground orchids on the edge". Plant Talk (31): 34–35.
  7. ^
    doi:10.11646/phytotaxa.334.1.12
    .
  8. ^ "Rhizanthella gardneri". APNI. Retrieved 26 September 2020.
  9. ^ Rogers, Richard Sanders (1928). "A New Genus of Australian Orchid". Journal of the Royal Society of Western Australia. 15 (1): 1–4. Retrieved 26 September 2020.
  10. ^
    Department of Biodiversity, Conservation and Attractions
    .
  11. ^ "Western Australia's Incredible Underground Orchid". ScienceDaily.com. ScienceDaily. 9 February 2011. Retrieved 10 February 2011.
  12. PMID 19619652
    .
  13. doi:10.1071/BT08031
    .

Further reading

  1. Reader's Digest Ltd. (1989). Facts and Fallacies - Stories of the Strange and Unusual. Reader's Digest Ltd. Page 39.
    ISBN 0-86438-087-9
    .
  2. Jones, David L. (2006). A complete guide to native orchids of Australia: including the island territories. Frenchs Forest.
    ISBN 1-877069-12-4
    .
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