Rhizanthella

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Underground orchids
Rhizanthella gardneri -- Fred Hort.jpg
Rhizanthella gardneri
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Orchidaceae
Subfamily: Orchidoideae
Tribe: Diurideae
Subtribe: Rhizanthellinae
R.S.Rogers
Genus: Rhizanthella
R.S.Rogers [1]
Type species
Rhizanthella gardneri
R.S.Rogers (1928)
Synonyms [2]

Cryptanthemis Rupp

Rhizanthella, commonly known as underground orchids, [3] is a genus of flowering plants in the orchid family, Orchidaceae and is endemic to Australia. All are leafless, living underground in symbiosis with mycorrhizal fungi. The inflorescence is a head of flowers held at, or just above the ground but mostly covered by soil or leaf litter and little is known about the mechanism of pollination.

Contents

Description

Orchids in the genus Rhizanthella are mostly underground, perennial, sympodial, mycotrophic herbs with fleshy underground stems which produce new shoots at nodes where there are colourless leaf-like cataphylls. There are no roots and new tubers form at the end of short stems. The leaves are reduced to scale-like structures lacking chlorophyll, pressed against and sheathing the stems. [3] [4] [5] [6]

The inflorescence is a head containing many flowers and is held at, or just above ground level but the head is usually covered with leaf litter or soil. The head is surrounded by a large number of overlapping bracts and each flower has an erect, elongated bract at its base. The flowers are non-resupinate, arranged in a spiral, inward-facing, dull coloured and lack a stalk. The sepals and petals form a short, curved hood over the labellum and column, open on one side. The lateral sepals are joined to each other and to the dorsal sepal at their bases. The petals are joined at their bases to the column and are shorter than the sepals. The labellum is different in size, shape and colouration from the other petals and sepals, is thick, fleshy and has no nectar. The column is short with short wings. Flowering time depends on species and is followed by the fruit which is a berry that does not split open (indehiscent) and which contains 50 to 100 seeds. [3] [4] [5] [6]

Underground orchids do not possess chloroplasts but they retain plastid genes, although R. gardneri possesses one of the smallest organelle genome yet described in land plants. [7]

Taxonomy and naming

The first formal description of an underground orchid was by Richard Sanders Rogers who published his description of R. gardneri in the Journal of the Royal Society of Western Australia in 1928. [8] [9] The name "Rhizanthella" is a diminutive of Rhizanthes , a parasitic plant in the Family Rafflesiaceae. [10] The name "Rhizanthes" is derived from the Ancient Greek words rhiza meaning "root" [11] :666 and anthos meaning "flower". [11] :338

Species list

Four species are recognised by the World Checklist of Selected Plant Families and a fifth species has been formally described, but not as yet accepted by other authorities:

In 2020, a fifth species, Rhizanthella speciosa , found in New South Wales, was described by Mark Clements and David Jones in the journal Lankesteriana but as at September 2020, the name has not been accepted by the World Checklist of Selected Plant Families. [16]

Distribution and habitat

Rhizanthella gardneri occurs in the south-west of Western Australia where it grows in association with broombush ( Melaleuca uncinata ). [3] R. johnstonii, also from WA, was split from R. gardneri in 2018. [17] [18] Rhizanthella omissa has only been collected once, at an elevation of 1,200 m (4,000 ft) in the Lamington National Park in Queensland. [19] Rhizanthella slateri , formerly known as Cryptanthemis slateri, occurs in the Blue Mountains and similar ranges in New South Wales where it grows in sclerophyll forest. [6] R. speciosa was discovered in 2016 in wet sclerophyll forest in Barrington Tops, which contrasts with the more-open dry forest habitat of R. slateri. [18]

Ecology

The pollination mechanism of Rhizanthella is not known. A single specimen of a small fly from the genus Megaselia , some small wasps and termites are the only observations of insects carrying pollinia of Rhizanthella. [4]

Related Research Articles

<i>Eulophia</i> Genus of orchids

Eulophia, commonly known as corduroy orchids, is a genus of about two hundred species of flowering plants in the orchid family, Orchidaceae. Most Eulophia orchids are terrestrial but some are deciduous while others are evergreen. They either have an underground rhizome or pseudobulbs on the surface and those species with leaves have them on the end of a fleshy stem. The flowers are arranged on a thin flowering spike, the flowers having sepals which are larger than the petals. The genus is widely distributed but most species are found in Africa and Asia, usually growing in shady places with grass or shrubs in forests.

<i>Rhizanthella slateri</i> Species of orchid

Rhizanthella slateri, commonly known as the eastern underground orchid, is a species of flowering plant in the orchid family and is endemic to New South Wales. It is a mycoheterotrophic herb that spends most of its life under the soil surface, its flowers only sometimes appearing a few millimetres about ground level.

<i>Rhizanthella gardneri</i> Species of orchid plant

Rhizanthella gardneri, commonly known as western underground orchid, 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.

<i>Caladenia</i> Genus of orchids

Caladenia, commonly known as spider orchids, is a genus of 350 species of plants in the orchid family, Orchidaceae. Spider orchids are terrestrial herbs with a single hairy leaf and a hairy stem. The labellum is fringed or toothed in most species and there are small projections called calli on the labellum. The flowers have adaptations to attract particular species of insects for pollination. The genus is divided into three groups on the basis of flower shape, broadly, spider orchids, zebra orchids and cowslip orchids, although other common names are often used. Although they occur in other countries, most are Australian and 136 species occur in Western Australia, making it the most species-rich orchid genus in that state.

<i>Cyrtostylis</i> Genus of plants

Cyrtostylis, commonly known as gnat orchids, is a genus of five or six species of flowering plants in the orchid family Orchidaceae and is native to Australia and New Zealand. Cyrtostylis orchids often form dense colonies of genetically identical plants. They have a single heart-shaped leaf and a thin flowering stem with pale coloured insect-like flowers. The lateral sepals and petals are similar in size and colour but the labellum is shelf-like and conspicuous with two prominent glands at its base.

<i>Liparis</i> (plant) Genus of plants

Liparis, commonly known as widelip orchids, sphinx orchids or 羊耳蒜属 is a cosmopolitan genus of more than 350 species of orchids in the family Orchidaceae. Plants in this genus are terrestrial, lithophytic or epiphytic herbs with a wide range of forms. The flowers are usually resupinate and small to medium sized, yellow, yellow-green or purplish with spreading sepals and petals. The labellum is usually larger than the sepals and petals and is lobed, sometimes with a toothed or wavy margin and one or two calli at its base.

<i>Adenochilus</i> Genus of flowering plants

Adenochilus, commonly known as gnome orchids is a genus of two species of flowering plants in the orchid family Orchidaceae, one endemic to New Zealand and the other to Australia. Both species have a long, horizontal, underground rhizome with a single leaf on the flowering stem and a single resupinate flower with its dorsal sepal forming a hood over the labellum and column.

<i>Arthrochilus</i> Genus of flowering plants

Arthrochilus, commonly called elbow orchids, is a genus of about fifteen species of flowering plants from the orchid family (Orchidaceae) and is found in Australia and New Guinea. The flowers are pollinated by male thynnid wasps which attempt to mate with the flower and are held in place by hooks while the pollinium is transferred between insect and flower.

<i>Cryptostylis</i> Species of orchid

Cryptostylis, commonly known as tongue orchids, is a genus of flowering plants from the orchid family. Tongue orchids are terrestrial herbs with one to a few stalked leaves at the base of the flowering stem, or leafless. One to a few dull coloured flowers are borne on an erect flowering stem. The most conspicuous part of the flower is the labellum, compared to the much reduced sepals and petals. At least some species are pollinated by wasps when they attempt to mate with the flower. There are about twenty five species found in South Asia, Southeast Asia and the South Pacific.

<i>Caleana</i> Genus of flowering plants

Caleana, commonly known as duck orchids, is a genus of flowering plants in the orchid family, Orchidaceae that is found in Australia and New Zealand. The Australian species are found in all states but have not been recorded in the Northern Territory. Duck orchids have a single leaf and one or a few, dull-coloured, inconspicuous flowers. Most species are found in Western Australia but one species occurs in eastern Australia and one occurs in eastern Australia and New Zealand. Orchids in this genus as well as the hammer orchids (Drakaea) are pollinated by male thynnid wasps.

<i>Corybas aconitiflorus</i> Species of orchid

Corybas aconitiflorus, commonly known as the cradle orchid or spurred helmet orchid, is a species of terrestrial orchid endemic to eastern Australia, occurring from south-east Queensland to Tasmania. The small flowers have a hooded appearance as the uppermost sepal hides most of the rest of the flower. It is the type species of the genus Corybas.

<i>Praecoxanthus</i> Genus of orchids

Praecoxanthus aphyllus, commonly known as leafless orchid, is the only species of the flowering plant genus Praecoxanthus in the orchid family, Orchidaceae and is endemic to the south-west of Western Australia. Plants in flower lack a true leaf, although those plants that are not flowering do possess a green leaf. This species is one of the first orchids to flower each year and its creamy white, fragrant flower easily distinguishes it from other species.

Caleana alcockii, commonly known as Alcock's duck orchid is a rare species of orchid endemic to the south-west of Western Australia. It has a single smooth leaf and is distinguished by its humped labellum and relatively late flowering period. It only occurs north of Geraldton.

Caleana parvula, commonly known as the Esperance duck orchid is a species of orchid endemic to a small area near Esperance in the south-west of Western Australia. It has a single smooth leaf and usually only a single greenish yellow and red flower. It is distinguished by its small flower with the calli only on the outer one-fifth of the labellum. The only other Caleana species in Western Australia which is smaller is C. lyonsii.

Corybas abditus, commonly known as the swamp helmet orchid or small helmet orchid , is a species of terrestrial orchid endemic to Western Australia. It is a rare orchid with a single bluish green, heart-shaped leaf and a small flower with an enlarged dorsal sepal and tube-shaped labellum.

<i>Corybas despectans</i> Species of orchid

Corybas despectans, commonly known as the tiny helmet orchid or sandhill helmet orchid is a species of terrestrial orchid endemic to southern Australia. It has round or heart-shaped leaf and a tiny reddish purple flower. Unlike many others in the genus, the dorsal sepal does not cover the labellum. It is similar to C. incurvus but the flowers are smaller.

Caladenia rosea is a plant in the orchid family Orchidaceae and is endemic to relatively inaccessible, high lateritic plateaux in a high rainfall area in south-western Western Australia. It is a terrestrial orchid with a single hairy leaf and up to three pink flowers on a thin, sparsely-hairy stem. It is similar to Caladenia flava but is distinguished by the perianth being pink to dark pink with prominent red striping and spotting on the dorsal sepal and lateral petals. Caladenia rosea mimics Hypocalymma robustum (Myrtaceae) in terms of flowering time, colour and scent.

Rhizanthella speciosa is a species of flowering plant in the orchid family and is endemic to Barrington Tops in New South Wales. It is a mycoheterotrophic herb that spends its entire life cycle, including flowering, at or below the soil surface. As at September 2020, R. speciosa has not yet been accepted as a valid name by the World Checklist of Selected Plant Families or the Australian Plant Census.

<i>Rhizanthella johnstonii</i> Species of orchid

Rhizanthella johnstonii, commonly known as south coast underground orchid, is a species of flowering plant in the orchid family and is endemic to the southwest of Western Australia. It is a subterranean herb that has a horizontal rhizome and a head of up to sixty small white flowers with a pink tinge, surrounded by relatively large, cream-coloured to pale pinkish cream bracts.

Rhizanthella omissa is a species of flowering plant in the orchid family and is found in the Lamington National Park in Queensland. It is a subterranean herb that grows in casuarina forest and flowers underground. It was first formally described in 2006 by David Jones and Mark Clements in the journal The Orchadian. The species is listed as "endangered" under the Queensland Government Nature Conservation Act 1992.

References

  1. "Rhizanthella". Kew Science - Plants of the World Online. Retrieved 25 September 2020.
  2. "Rhizanthella". World Checklist of Selected Plant Families (WCSP). Royal Botanic Gardens, Kew . Retrieved 20 July 2016.
  3. 1 2 3 4 Hoffman, Noel; Brown, Andrew (2011). Orchids of South-West Australia (3rd ed.). Gooseberry Hill: Noel Hoffman. pp. 386–389. ISBN   9780646562322.
  4. 1 2 3 Alec M. Pridgeon; Phillip J. Cribb; Mark W. Chase; Finn N. Rasmussen, eds. (2001). Genera Orchidacearum, Volume 2, Orchidoideae (part 1). Oxford, England: Oxford University Press. pp. 186–193. ISBN   0198507100.
  5. 1 2 "Rhizanthella". FloraBase . Western Australian Government Department of Biodiversity, Conservation and Attractions.
  6. 1 2 3 Weston, Peter H. "Genus Rhizanthella". Royal Botanic Garden Sydney: plantnet. Retrieved 20 July 2016.
  7. Delannoy, Etienne; Fujii, Sota; Colas des Francs-Small, Catherine; Brundrett, Mark; Small, Ian (2 February 2011). "Rampant Gene Loss in the Underground Orchid Rhizanthella gardneri Highlights Evolutionary Constraints on Plastid Genomes". Molecular Biology and Evolution. 28 (7): 2077–2086. doi:10.1093/molbev/msr028. PMC   3112369 . PMID   21289370.
  8. "Rhizanthella gardneri". APNI. Retrieved 20 July 2016.
  9. Rogers, Richard Sanders (1928). "A New Genus of Australian Orchid". Journal of the Royal Society of Western Australia. 15 (1): 1. Retrieved 26 September 2020.
  10. Quattrocchi, Umberto (2000). R - Z. Boca Raton, FL: CRC World Dictionary of Pant Names (R-Z). p. 2296. ISBN   0849326788.
  11. 1 2 Brown, Roland Wilbur (1956). The Composition of Scientific Words. Washington, D.C.: Smithsonian Institution Press.
  12. "Rhizanthella gardneri". Kew Science - Plants of the World Online. Retrieved 25 September 2020.
  13. "Rhizanthella johnstonii". Kew Science - Plants of the World Online. Retrieved 25 September 2020.
  14. "Rhizanthella omissa". Kew Science - Plants of the World Online. Retrieved 25 September 2020.
  15. "Rhizanthella slateri". Kew Science - Plants of the World Online. Retrieved 25 September 2020.
  16. "Rhizanthella speciosa". APNI. Retrieved 27 September 2020.
  17. Dixon, Kingsley W.; Christenhusz, Maarten J. M. (2018-01-12). "Flowering in darkness: a new species of subterranean orchid Rhizanthella (Orchidaceae; Orchidoideae; Diurideae) from Western Australia". Phytotaxa. 334 (1): 75–79. doi:10.11646/phytotaxa.334.1.12. ISSN   1179-3163.
  18. 1 2 Clements, Mark A.; Jones, David L. (2020-07-30). "Notes on Australasian Orchids 6: A new species of Rhizanthella (Diurideae, subtribe Prasophyllinae) from Eastern Australia". Lankesteriana: 221–227–221–227. doi: 10.15517/lank.v20i2.43271 . ISSN   2215-2067.
  19. "Rhizanthella omissa". Internet Orchid Species Photo Encyclopedia. Retrieved 20 July 2016.

Further reading