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

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of flowering plants in the orchid family,

Orchidaceae Orchids are plants that belong to the family (biology), family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Orchids are cosmopolitan distribution, cosmopolitan plants that ...

and is

endemic Endemism is the state of a species being found only 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 foun ...

to Australia. All are leafless, living underground in

symbiosis Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biological interaction, between two organisms of different species. The two organisms, termed symbionts, can fo ...

with

mycorrhiza A mycorrhiza (; , 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's rhizosphere, the plant root system and its surroundings. Mycorrhizae play ...

l fungi. The

inflorescence In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...

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 (botany), stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example bees, beetles or bu ...

Description

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

perennial In horticulture, the term perennial ('' per-'' + '' -ennial'', "through the year") is used to differentiate a plant from shorter-lived annuals and biennials. It has thus been defined as a plant that lives more than 2 years. The term is also ...

sympodial In botany, 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, als ...

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 Herbs are a widely distributed and widespread group of plants, excluding vegetables, with savory or aromatic properties that are used for flavoring and garnish (food), garnishing food, for medicinal purposes, or for fragrances. Culinary use typi ...

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). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines, ...

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 that plants use as storage organs for nutrients, derived from stems or roots. Tubers help plants perennate (survive winter or dry months), provide energy and nutrients, and are a means of asexual reproduc ...

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

chlorophyll Chlorophyll 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 allows plants to absorb energy ...

, 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, associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves in size, color, shape or texture. They also lo ...

s 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

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 Etymology The term ''sepalum'' ...

s and

petal Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...

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 also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

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 The fus ...

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 viscous, sugar-rich liquid produced by Plant, plants in glands called nectaries, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to an ...

. 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 ...

) and which contains 50 to 250 minute seeds. Underground orchids do not possess chloroplasts but they retain

plastid A plastid is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria. Examples of plastids include chloroplasts ...

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

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

genome 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 genes, other functional regions of the genome such as ...

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 ...

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, and also gained the "Royal" name in the same year. It publishes the ''Journal of the Royal Society of Western Australia'', and has ...

'' 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 e ...

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

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

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

Species list

Five species are recognised by the

Plants of the World Online Plants of the World Online (POWO) is an online taxonomic database published by the Royal Botanic Gardens, Kew. History Following the Convention on Biological Diversity, the Royal Botanic Gardens in Kew launched Plants of the World Online i ...

: * '' Rhizanthella gardneri'' R.S.Rogers – western underground orchid (W.A.) * '' Rhizanthella johnstonii'' K.W.Dixon & Christenh. – south coast underground orchid (W.A.) * '' Rhizanthella omissa'' D.L.Jones & M.A.Clem. (Qld.) * '' Rhizanthella slateri'' ( Rupp) M.A.Clem. & P.J.Cribb – eastern Australian underground orchid (N.S.W.) * '' Rhizanthella speciosa'' M.A.Clem. & D.L.Jones (N.S.W.)

Distribution and habitat

'' Rhizanthella gardneri'' occurs in the south-west of

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

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

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

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

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

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

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 leaves, short Internode (botany), internodes (the distance between leaves along the stem) and leaf orientation which is parallel or ...

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 The Phoridae are a family of small, hump-backed flies resembling fruit flies. Phorid flies can often be identified by their escape habit of running rapidly across a surface rather than ...

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

pollinia A pollinium (: 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 milkwee ...

of ''Rhizanthella''.

Description

Taxonomy and naming

Species list

Distribution and habitat

Ecology

References

Further reading