''Rhizanthella'', commonly known as underground orchids, is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of flowering plants in the orchid family,

Orchidaceae Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Along with the Asteraceae, they are one of the two largest families of flowering ...

and is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to Australia. All are leafless, living underground in

symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

with

mycorrhiza A mycorrhiza (from Greek μύκης ', "fungus", and ῥίζα ', "root"; pl. mycorrhizae, mycorrhiza or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant ...

l fungi. The

inflorescence An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed o ...

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 Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds ...

Description

Orchids in the genus ''Rhizanthella'' are mostly underground,

perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...

sympodial Sympodial growth is a bifurcating branching pattern where one branch develops more strongly than the other, resulting in the stronger branches forming the primary shoot and the weaker branches appearing laterally. A sympodium, also referred to a ...

mycotrophic A mycotroph is a plant that gets all or part of its carbon, water, or nutrient supply through symbiotic association with fungi. The term can refer to plants that engage in either of two distinct symbioses with fungi: *Many mycotrophs have a mut ...

herbs In general use, herbs are a widely distributed and widespread group of plants, excluding vegetables and other plants consumed for macronutrients, with savory or aromatic properties that are used for flavoring and garnishing food, for medicinal ...

with fleshy underground stems which produce new shoots at

nodes In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two ...

where there are colourless leaf-like

cataphyll In plant morphology, a cataphyll (sometimes also called a ''cataphyllum'' or cataphyll leafJackson, Benjamin, Daydon; A Glossary of Botanic Terms with their Derivation and Accent; Published by Gerald Duckworth & Co. London, 4th ed 1928) is a reduce ...

s. There are no roots and new

tuber Tubers are a type of enlarged structure used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing ...

s form at the end of short stems. The leaves are reduced to scale-like structures lacking

chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...

, pressed against and sheathing the stems. 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

bract In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...

s and each flower has an erect, elongated bract at its base. The flowers are non-

resupinate Resupination is derived from the Latin word ''resupinus'', meaning "bent back with the face upward" or "on the back". "Resupination" is the noun form of the adjective "resupine" which means "being upside-down, supine or facing upward". The word " ...

, arranged in a spiral, inward-facing, dull coloured and lack a stalk. The

sepal A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 The term ''sepalum'' was coined b ...

s and

petal Petals are modified Leaf, leaves that surround the reproductive parts of flowers. They are often advertising coloration, brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''c ...

s form a short, curved hood over the labellum and

column A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. ...

, open on one side. The

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...

sepals are joined to each other and to the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

sepal at their bases. The petals are joined at their bases to the

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 Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists ...

. 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 Dehiscence is the splitting of a mature plant structure along a built-in line of weakness to release its contents. This is common among fruits, anthers and sporangia. Sometimes this involves the complete detachment of a part; structures that op ...

) and which contains 50 to 100 seeds. Underground orchids do not possess chloroplasts but they retain

plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosy ...

genes, although '' R. gardneri'' possesses the smallest

organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

yet described in land plants.

Taxonomy and naming

The first formal description of an underground orchid was by

Richard Sanders Rogers Richard Sanders Rogers (2 December 1861 – 28 March 1942) was a distinguished Australian medical doctor, and world authority on Australasian orchids. He described over 80 Australian orchid species, three from New Zealand and 30 from New Guinea a ...

who published his description of '' R. gardneri'' in the ''

Journal of the Royal Society of Western Australia The Royal Society of Western Australia (RSWA) promotes science in Western Australia. The RSWA was founded in 1914. It publishes the ''Journal of the Royal Society of Western Australia'', and has awarded the Medal of the Royal Society of Western ...

'' in 1928. The name "''Rhizanthella''" is a diminutive of ''

Rhizanthes ''Rhizanthes'' is a genus of four species of parasitic flowering plants in the family Rafflesiaceae. They are without leaves, stems, roots, or photosynthetic tissue, and grow within the roots of a few species of ''Tetrastigma'' vines. The genus i ...

'', a parasitic plant in the Family

Rafflesiaceae The Rafflesiaceae are a family of rare parasitic plants comprising 36 species in 3 genera found in the tropical forests of east and southeast Asia, including ''Rafflesia arnoldii'', which has the largest flowers of all plants. The plants are end ...

. The name "''Rhizanthes''" is derived from the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

words ''rhiza'' meaning "root" and ''anthos'' meaning "flower".

Species list

Four species are recognised by the

World Checklist of Selected Plant Families The World Checklist of Selected Plant Families (usually abbreviated to WCSP) is an "international collaborative programme that provides the latest peer reviewed and published opinions on the accepted scientific names and synonyms of selected plan ...

and a fifth species has been formally described, but not as yet accepted by other authorities: * ''

Rhizanthella gardneri ''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 flowerin ...

R.S.Rogers Richard Sanders Rogers (2 December 1861 – 28 March 1942) was a distinguished Australians, Australian medical doctor, and world authority on Australasian orchids. He described over 80 Australian orchid species, three from New Zealand and 30 from ...

– western underground orchid (W.A.) * '' Rhizanthella johnstonii'' K.W.Dixon &

Christenh. Dr Maarten Joost Maria Christenhusz (born 27 April 1976) is a Dutch botanist, natural historian and photographer. Career He was born in Enschede, the Netherlands, received his undergraduate and master's degrees from Utrecht University in ...

– south coast underground orchid (W.A.) * ''

Rhizanthella omissa ''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 descri ...

D.L.Jones David Lloyd Jones (born 1944) is an Australians, Australian horticultural botanist and the author of many books and papers, especially on Australian orchids. Jones was born in Victoria (Australia), Victoria and in his youth was a student at Burnl ...

& M.A.Clem. (Qld.) * ''

Rhizanthella slateri ''Rhizanthella slateri'', commonly known as the eastern underground orchid, is a species of flowering plant in the orchid family and is Endemism, endemic to New South Wales. It is a Myco-heterotrophy, mycoheterotrophic Herbaceous plant, herb that ...

'' ( Rupp) M.A.Clem. & P.J.Cribb – eastern Australian underground orchid (N.S.W.) 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.

Distribution and habitat

'' occurs in the south-west of

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...

where it grows in association with broombush (''

Melaleuca uncinata ''Melaleuca uncinata'', commonly known as broombush, broom honeymyrtle or brushwood, is a plant in the paperbark family native to southern Australia. It is harvested from the wild, and grown in plantations, for broombush fencing. The Noongar nam ...

''). R. johnstonii, also from WA, was split from R. gardneri in 2018. ''

'' has only been collected once, at an elevation of in the

Lamington National Park The Lamington National Park is a national park, lying on the Lamington Plateau of the McPherson Range on the Queensland/New South Wales border in Australia. From Southport on the Gold Coast the park is to the southwest and Brisbane is north. Th ...

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...

. ''

'', formerly known as ''Cryptanthemis slateri,'' occurs in the Blue Mountains and similar ranges in

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

where it grows in

sclerophyll Sclerophyll is a type of vegetation that is adapted to long periods of dryness and heat. The plants feature hard leaf, leaves, short Internode (botany), internodes (the distance between leaves along the stem) and leaf orientation which is paral ...

forest. '' R. speciosa'' was discovered in 2016 in wet sclerophyll forest in

Barrington Tops Barrington Tops is part of the Great Dividing Range in New South Wales, Australia, between Gloucester and Scone. In 1934, the area was difficult to access and was described as being "not traceable to any man-made feature". Part of the area has ...

, which contrasts with the more-open dry forest habitat of ''R. slateri''.

Ecology

The pollination mechanism of ''Rhizanthella'' is not known. A single specimen of a small fly from the genus ''

Megaselia ''Megaselia'' is a genus of flies in the family Phoridae. See also * List of Megaselia species This is a list of 1675 species in '' Megaselia'', a genus of scuttle flies in the family Phoridae. ''Megaselia'' species A * ''Megaselia abaliena ...

'', some small wasps and termites are the only observations of insects carrying

pollinia A pollinium (plural pollinia) is a coherent mass of pollen grains in a plant that are the product of only one anther, but are transferred, during pollination, as a single unit. This is regularly seen in plants such as orchids and many species of mil ...

of ''Rhizanthella''.

Description

Taxonomy and naming

Species list

Distribution and habitat

Ecology

References

Further reading