Rhizanthella

{{Short description|Genus of flowering plants}} {{Automatic taxobox | name = Underground orchids | image = Rhizanthella gardneri — Fred Hort.jpg | image_caption = ''[[Rhizanthella gardneri]]'' | display_parents = 3 | parent_authority = R.S.Rogers | taxon = Rhizanthella | authority = [[Richard Sanders Rogers|R.S.Rogers]]<ref name="POWO">{{cite web |title=''Rhizanthella'' |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:30516-1#synonyms |publisher=Plants of the World Online |access-date=13 May 2025}}</ref> | type_species = ''Rhizanthella gardneri'' | type_species_authority = [[R.S.Rogers]] (1928) | synonyms_ref = <ref name="POWO" /> | synonyms = ''Cryptanthemis'' [[Herman Rupp|Rupp]] }}

'''''Rhizanthella''''', commonly known as '''underground orchids''',<ref name="Hoffman" /> is a [[genus]] of flowering plants in the orchid family, [[Orchidaceae]] and is [[Endemism|endemic]] to Australia. All are leafless, living underground in [[symbiosis]] with [[mycorrhiza]]l 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]].

==Description== Orchids in the genus ''Rhizanthella'' are mostly underground, [[Perennial plant|perennial]], [[sympodial]], [[mycotrophic]] [[Herbaceous plant|herbs]] with fleshy underground stems which produce new shoots at [[Plant stem|nodes]] where there are colourless leaf-like [[cataphyll]]s. There are no roots and new [[tuber]]s form at the end of short stems. The leaves are reduced to scale-like structures lacking [[chlorophyll]], pressed against and sheathing the stems.<ref name="Hoffman">{{cite book|last1=Hoffman|first1=Noel|last2=Brown|first2=Andrew|title=Orchids of South-West Australia.|date=2011|publisher=Noel Hoffman|location=Gooseberry Hill|isbn=9780646562322|pages=386–389|edition=3rd}}</ref><ref name="Orchids">{{cite book|editor1=Alec M. Pridgeon |editor2=Phillip J. Cribb |editor3=Mark W. Chase |editor4=Finn N. Rasmussen |title=Genera Orchidacearum, Volume 2, Orchidoideae (part 1)|date=2001|publisher=Oxford University Press|location=Oxford, England|isbn=0198507100|pages=186–193}}</ref><ref name=FloraBase>{{FloraBase|name=''Rhizanthella''|id=21295}}</ref><ref name="RBGS">{{cite web|last1=Weston|first1=Peter H.|title=Genus ''Rhizanthella''|url=http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&showsyn=&dist=&constat=&lvl=gn&name=Rhizanthella|publisher=Royal Botanic Garden Sydney: plantnet|access-date=20 July 2016}}</ref>

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]]s and each flower has an erect, elongated bract at its base. The flowers are non-[[Resupination#Orchidaceae|resupinate]], arranged in a spiral, inward-facing, dull coloured and lack a stalk. The [[sepal]]s and [[petal]]s form a short, curved hood over the [[Labellum (botany)|labellum]] and [[Column (botany)|column]], open on one side. The [[wikt:lateral|lateral]] sepals are joined to each other and to the [[wikt:dorsal|dorsal]] sepal at their bases. The petals are joined at their bases to the [[Column (botany)|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 ([[Dehiscence (botany)|indehiscent]]) and which contains 50 to 250 minute seeds.<ref name="Hoffman" /><ref name="Orchids" /><ref name="FloraBase" /><ref name="RBGS" />

Underground orchids do not possess chloroplasts but they retain [[plastid]] genes, although ''[[Rhizanthella gardneri|R. gardneri]]'' possesses one of the smallest [[organelle]] [[genome]] yet described in land plants.<ref name="Oxford">{{cite journal|last1=Delannoy|first1=Etienne|last2=Fujii|first2=Sota|last3=Colas des Francs-Small|first3=Catherine|last4=Brundrett|first4=Mark|last5=Small|first5=Ian|title=Rampant Gene Loss in the Underground Orchid Rhizanthella gardneri Highlights Evolutionary Constraints on Plastid Genomes|journal=Molecular Biology and Evolution|date=2 February 2011|volume=28|issue=7|pages=2077–2086|doi=10.1093/molbev/msr028|pmid=21289370|pmc=3112369}}</ref>

==Taxonomy and naming== The first formal description of an underground orchid was by [[Richard Sanders Rogers]] who published his description of ''[[Rhizanthella gardneri|R. gardneri]]'' in the ''[[Royal Society of Western Australia|Journal of the Royal Society of Western Australia]]'' in 1928.<ref name=APNI>{{cite web|title=''Rhizanthella gardneri''|url= http://id.biodiversity.org.au/instance/apni/477139|publisher=APNI|access-date=20 July 2016}}</ref><ref name="R.S.Rogers">{{cite journal |last1=Rogers |first1=Richard Sanders |title=A New Genus of Australian Orchid |journal=Journal of the Royal Society of Western Australia |date=1928 |volume=15 |issue=1 |page=1 |url=https://www.biodiversitylibrary.org/item/173678#page/53/mode/1up |access-date=26 September 2020}}</ref> The name "''Rhizanthella''" is a diminutive of ''[[Rhizanthes]]'', a parasitic plant in the Family [[Rafflesiaceae]].<ref name="Quattrocchi">{{cite book|last1=Quattrocchi|first1=Umberto|title=R - Z.|date=2000|publisher=CRC World Dictionary of Pant Names (R-Z)|location=Boca Raton, FL|isbn=0849326788|page=2296}}</ref> The name "''Rhizanthes''" is derived from the [[Ancient Greek]] words ''rhiza'' meaning "root"<ref name="RWB">{{cite book|last1=Brown|first1=Roland Wilbur|title=The Composition of Scientific Words|date=1956|publisher=Smithsonian Institution Press|location=Washington, D.C.}}</ref>{{rp|666}} and ''anthos'' meaning "flower".<ref name="RWB" />{{rp|338}}

===Species list=== Five species are recognised by the [[Plants of the World Online]]: * ''[[Rhizanthella gardneri]]'' [[R.S.Rogers]]<ref name="POWO1">{{cite web |title=''Rhizanthella gardneri'' |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:655670-1 |publisher=Kew Science - Plants of the World Online |access-date=25 September 2020}}</ref> – western underground orchid (W.A.) * ''[[Rhizanthella johnstonii]]'' [[Kingsley Wayne Dixon|K.W.Dixon]] & [[Maarten J. M. Christenhusz|Christenh.]]<ref name="POWO2">{{cite web |title=''Rhizanthella johnstonii'' |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77176525-1 |publisher=Kew Science - Plants of the World Online |access-date=25 September 2020}}</ref> – south coast underground orchid (W.A.) * ''[[Rhizanthella omissa]]'' [[David L. Jones (botanist)|D.L.Jones]] & [[Mark Alwin Clements|M.A.Clem.]]<ref name="POWO3">{{cite web |title=''Rhizanthella omissa'' |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77077242-1 |publisher=Kew Science - Plants of the World Online |access-date=25 September 2020}}</ref> (Qld.) * ''[[Rhizanthella slateri]]'' ([[Herman Rupp|Rupp]]) M.A.Clem. & [[Phillip James Cribb|P.J.Cribb]]<ref name="POWO4">{{cite web |title=''Rhizanthella slateri'' |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:75519-3 |publisher=Kew Science - Plants of the World Online |access-date=25 September 2020}}</ref> – eastern Australian underground orchid (N.S.W.) * ''[[Rhizanthella speciosa]]'' M.A.Clem. & D.L.Jones<ref name="POWO5">{{cite web |title=''Rhizanthella speciosa'' |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77219091-1 |publisher=Kew Science - Plants of the World Online |access-date=13 May 2025}}</ref> (N.S.W.)

==Distribution and habitat== ''[[Rhizanthella gardneri]]'' occurs in the south-west of [[Western Australia]] where it grows in association with broombush (''[[Melaleuca uncinata]]'').<ref name="Hoffman" /> [[Rhizanthella johnstonii|''R. johnstonii'']], also from WA, was split from ''R. gardneri'' in 2018.<ref>{{Cite journal|last=Dixon|first=Kingsley W.|last2=Christenhusz|first2=Maarten J. M.|date=2018-01-12|title=Flowering in darkness: a new species of subterranean orchid Rhizanthella (Orchidaceae; Orchidoideae; Diurideae) from Western Australia|url=https://www.biotaxa.org/Phytotaxa/article/view/phytotaxa.334.1.12|journal=Phytotaxa|language=en|volume=334|issue=1|pages=75–79|doi=10.11646/phytotaxa.334.1.12|issn=1179-3163|url-access=subscription}}</ref><ref name="ClementsJones2020" /> ''[[Rhizanthella omissa]]'' has only been collected once, at an elevation of {{convert|1200|m|ft|sigfig=1|abbr=on}} in the [[Lamington National Park]] in [[Queensland]].<ref name="orchidspecies">{{cite web|title=''Rhizanthella omissa''|url=http://www.orchidspecies.com/rhizomissa.htm|publisher=Internet Orchid Species Photo Encyclopedia|access-date=20 July 2016}}</ref> ''[[Rhizanthella slateri]]'', formerly known as ''Cryptanthemis slateri,'' occurs in the [[Blue Mountains (New South Wales)|Blue Mountains]] and similar ranges in [[New South Wales]] where it grows in [[sclerophyll]] forest.<ref name="RBGS" /> ''[[Rhizanthella speciosa|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''.<ref name="ClementsJones2020">{{Cite journal|last=Clements|first=Mark A.|last2=Jones|first2=David L.|date=2020-07-30|title=Notes on Australasian Orchids 6: A new species of Rhizanthella (Diurideae, subtribe Prasophyllinae) from Eastern Australia|url=https://revistas.ucr.ac.cr/index.php/lankesteriana/article/view/43271|journal=Lankesteriana|language=en|pages=221–227–221–227|doi=10.15517/lank.v20i2.43271|issn=2215-2067|doi-access=free}}</ref>

==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''.<ref name="Orchids" />

==References== {{Reflist}}

==Further reading== * Jones, David L. (2006).'' A complete guide to native orchids of Australia: including the island territories''. Frenchs Forest. {{ISBN|1-877069-12-4}}. * [https://web.archive.org/web/20080311222734/http://www.arkive.org/species/GES/plants_and_algae/Rhizanthella_gardneri/ Underground orchid - Rhizanthella gardneri] at ARKive.org (includes photographs) * {{Commons-inline|Rhizanthella|''Rhizanthella''}}

[[Category:Rhizanthella| ]] [[Category:Diurideae genera]] [[Category:Endemic orchids of Australia]] [[Category:Myco-heterotrophic orchids]]