# Acianthus

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Genus of flowering plants

Acianthus Acianthus exsertus Scientific classification Kingdom: Plantae Clade: Embryophytes Clade: Tracheophytes Clade: Spermatophytes Clade: Angiosperms Clade: Monocots Order: Asparagales Family: Orchidaceae Subfamily: Orchidoideae Tribe: Diurideae Subtribe: Acianthinae Genus: Acianthus R.Br.[1] Synonyms[1] List Acianthella D.L.Jones & M.A.Clem. Acianthopsis M.A.Clem. & D.L.Jones Acianthopsis Szlach. nom. illeg. Acianthus R.Br. sect. Acianthus Acianthus sect. Macropetalus Kores Acianthus R.Br. subg. Acianthus Acianthus subg. Univiscidiati Kores Acianthus subg. Univiscidiatus Kores orth. var. Nemacianthus D.L.Jones & M.A.Clem. Univiscidiatus Szlach. nom. inval. Univiscidiatus D.L.Jones, M.A.Clem., I.K.Sharma, A.M.Mack. & Molloy nom. inval. Univiscidiatus sect. Macropetalus Szlach. nom. inval.

***Acianthus***, commonly known as **mosquito orchids**, is a [genus](/source/Genus) of about twelve [species](/source/Species) of [plants](/source/Plant) in the orchid [family](/source/Family_(taxonomy)), [Orchidaceae](/source/Orchidaceae). Mosquito orchids are [terrestrial](/source/Terrestrial_plant) [herbs](/source/Herbaceous_plant) with a single, heart-shaped, usually ground-hugging leaf and one to many small, green, pinkish or purplish flowers on a fleshy stalk. They are found in [New Caledonia](/source/New_Caledonia), [Australia](/source/Australia) and [New Zealand](/source/New_Zealand).

## Description

Orchids in the genus *Acianthus* are [terrestrial](/source/Terrestrial_plant), [perennial](/source/Perennial_plant), [deciduous](/source/Deciduous), [sympodial](/source/Sympodial) herbs with a single egg-shaped, heart-shaped or lobed leaf at the base. They have small, roughly spherical, underground [tubers](/source/Tuber) from which the flower stems arise. Lacking true roots, they have root-like [stolons](/source/Stolon) which develop "daughter" tubers at their ends. These orchids spend the dry, summer months dormant until, following late-summer or autumn rains, the leaf appears. The leaf is [glabrous](https://en.wiktionary.org/wiki/glabrous), sometimes ground-hugging, more usually held above the ground and is often purplish-red on the lower surface. Sometimes the leaves of plants with flowers are different from those lacking them. The leaves of all Australian species are very similar, making them hard to identify to species level in the absence of flowers.[2][3][4][5][6][7][8][9]

Flowers appear in the cooler months, usually in autumn, winter or spring, There are one to many [resupinate](/source/Resupination) small, green, pinkish or purplish flowers 4 to 5 mm (0.16 to 0.20 in) in diameter. The flowers are held on an upright, narrow but fleshy stalk, blend in with their surrounding and often resemble mosquitoes. The [sepals](/source/Sepal) are longer than the [petals](/source/Petal) and usually have a long, thin extension on their end. The [dorsal](https://en.wiktionary.org/wiki/dorsal) sepal is broader than the [lateral](https://en.wiktionary.org/wiki/lateral) ones and sometimes forms a hood over the [column](/source/Column_(botany)). The [lateral](https://en.wiktionary.org/wiki/lateral) sepals project forward beneath the [labellum](/source/Labellum_(botany)) and the petals spread widely or curve backwards against the ovary. The labellum is heart-shaped and has a prominent [callus](/source/Labellum_(botany)). The fruit is a thin-walled, glabrous [capsule](/source/Capsule_(botany)), containing a large number of winged seeds.[2][4][8][9]

## Taxonomy and naming

The genus was first formally described by [Robert Brown](/source/Robert_Brown_(Scottish_botanist_from_Montrose)) in 1810 in *[Prodromus Florae Novae Hollandiae](/source/Prodromus_Florae_Novae_Hollandiae)*. He described three species (*[A. fornicatus](/source/Acianthus_fornicatus)*, *[A. exsertus](/source/Acianthus_exsertus)* and *[A. caudatus](/source/Acianthus_caudatus)*) but did not nominate a [type species](/source/Type_species).[10][11] Orchids in this genus are closely related to those in the genus *[Caladenia](/source/Caladenia)*.[3]

The genus name (*Acianthus*) is derived from the Greek *ake* or *akis*, "a point, needle" and *anthos* "flower" referring to the pointed [perianth](https://en.wiktionary.org/wiki/perianth) and the [acuminate](https://en.wiktionary.org/wiki/acuminate) floral segments.[12][13]

### Species

The following is a list of *Acianthus* species accepted by [Australian Plant Census](/source/Australian_Plant_Census) as at March 2025, apart from *A. sinclairii* that is accepted by the [New Zealand Plant Conservation Network](/source/New_Zealand_Plant_Conservation_Network):[14][13]

- *[Acianthus apprimus](/source/Acianthus_apprimus)* [D.L.Jones](/source/D.L.Jones) – early mosquito orchid (New South Wales)

- *[Acianthus borealis](/source/Acianthus_borealis)* [D.L.Jones](/source/D.L.Jones) – northern mosquito orchid (Queensland)

- *[Acianthus caudatus](/source/Acianthus_caudatus)* [R.Br.](/source/R.Br.) – mayfly orchid (Queensland, New South Wales, Victoria, South Australia and Tasmania)

- *[Acianthus collinus](/source/Acianthus_collinus)* D.L.Jones – hooded mosquito orchid (New South Wales, the Australian Capital Territory, Victoria)

- *[Acianthus cuneatus](/source/Acianthus_cuneatus)* D.L.Jones & [L.M.Copel.](/source/L.M.Copel.) (New South Wales)

- *[Acianthus exiguus](/source/Acianthus_exiguus)* D.L.Jones – tiny mosquito orchid (New South Wales)

- *[Acianthus exsertus](/source/Acianthus_exsertus)* R.Br. – gnat orchid, large mosquito orchid (Queensland, New South Wales, ACT, Victoria )

- *[Acianthus fornicatus](/source/Acianthus_fornicatus)* R.Br. – pixie-caps (Queensland, New South Wales, Victoria)

- *[Acianthus ledwardii](/source/Acianthus_ledwardii)* [Rupp](/source/Montague_Rupp) – Ledward's mosquito orchid (Queensland)

- *[Acianthus pusillus](/source/Acianthus_pusillus)* D.L.Jones – small mosquito orchid (Queensland, New South Wales, Victoria, South Australia, Tasmania)

- *[Acianthus saxatilis](/source/Acianthus_saxatilis)* D.L.Jones & [M.A.Clem.](/source/M.A.Clem.) (Queensland)

- *[Acianthus scopulus](https://en.wikipedia.org/w/index.php?title=Acianthus_scopulus&action=edit&redlink=1)* D.L.Jones (New South Wales)

- *[Acianthus sinclairii](/source/Acianthus_sinclairii)* [Hook.f.](/source/Hook.f.) – heart-leaved orchid, pixie cap ([New Zealand](/source/New_Zealand))

[Plants of the World Online](/source/Plants_of_the_World_Online) considers *[A. apprimus](/source/Acianthus_apprimus)*, *[A. borealis](/source/Acianthus_borealis)*, *[A. collinus](/source/Acianthus_collinus)*, *[A. exiguus](/source/Acianthus_exiguus)* to be [synonyms](/source/Synonym_(taxonomy)) of *[A. fornicatus](/source/Acianthus_fornicatus)*.[15]

## Distribution and habitat

Of the Australian species of *Acianthus*, 9 are found in [New South Wales](/source/New_South_Wales), 6 in [Queensland](/source/Queensland), 3 in [Victoria](/source/Victoria_(Australia)) and 2 in [South Australia](/source/South_Australia). The sole New Zealand example, *[A. sinclairii](/source/Acianthus_sinclairii)* occurs on both [North](/source/North_Island) and [South](/source/South_Island) Islands, as well as on [Raoul](/source/Raoul_Island), [Stewart](/source/Stewart_Island), [Chatham](/source/Chatham_Island) and [Three Kings](/source/Three_Kings_Islands) Islands.[6][13]

Mosquito orchids species grow in small groups in forests on decaying litter, occasionally on partially decayed logs. They sometimes form dense [vegetative](/source/Vegetative_reproduction) colonies, in sheltered forest or heathland, and are often found underneath shrubs and bracken.[3]

## Ecology

The labellum of *Acianthus* species produces a sweet nectar which is contained in a sunken area at the base of the labellum. The flowers of Australian species open in sequence up the flowering spike, each flower open for a few days, and are [pollinated](https://en.wiktionary.org/wiki/pollinate) by [fungus gnats](/source/Fungus_gnat) from the families [Anisopodidae](/source/Anisopodidae), [Sciaridae](/source/Sciaridae) and [Mycetophilidae](/source/Mycetophilidae). Usually only a small percentage of the plants in a colony have flowers. Flies on *[Acianthus caudatus](/source/Acianthus_caudatus)* have been observed to move up the labellum, probing with their [proboscis](/source/Proboscis#Invertebrates) until they reach the nectar, where the up and down "pumping" action of their bodies brings them into contact with the [viscidium](/source/Pollinium) and pollinia which then adhere to the insect's body. When these are carried to another flower, a similar action causes the pollinia to attach to the receptive [stigma](/source/Stigma_(botany)).[2][4][6][9]

## Use in horticulture

Mosquito orchids are easy to grow in plastic or ceramic pots. They need to be watered regularly except when dormant over summer and to be repotted every one or two years.[6][16]

## References

1. ^ [***a***](#cite_ref-APC_1-0) [***b***](#cite_ref-APC_1-1) ["*Acianthus*"](https://biodiversity.org.au/nsl/services/apc-format/display/73143). *Australian Plant Census*. Retrieved 11 November 2022.

1. ^ [***a***](#cite_ref-Jones_2-0) [***b***](#cite_ref-Jones_2-1) [***c***](#cite_ref-Jones_2-2) Jones, David L. (2006). *A complete guide to native orchids of Australia including the island territories*. Frenchs Forest, N.S.W.: New Holland. p. 161. [ISBN](/source/ISBN_(identifier)) [1-877069-12-4](https://en.wikipedia.org/wiki/Special:BookSources/1-877069-12-4).

1. ^ [***a***](#cite_ref-Hoffman_3-0) [***b***](#cite_ref-Hoffman_3-1) [***c***](#cite_ref-Hoffman_3-2) Hoffman, Noel; Brown, Andrew (1984). *Orchids of south-west Australia* (2 ed.). Nedlands, W.A.: University of Western Australia Press. p. 189. [ISBN](/source/ISBN_(identifier)) [0855642262](https://en.wikipedia.org/wiki/Special:BookSources/0855642262).

1. ^ [***a***](#cite_ref-Bishop_4-0) [***b***](#cite_ref-Bishop_4-1) [***c***](#cite_ref-Bishop_4-2) Bishop, Anthony (1996). *Field guide to the orchids of New South Wales and Victoria*. Sydney: UNSW Press. p. 172. [ISBN](/source/ISBN_(identifier)) [086840375X](https://en.wikipedia.org/wiki/Special:BookSources/086840375X).

1. **[^](#cite_ref-Backhouse_5-0)** Backhouse, Gary; Jeanes, Jeffrey (1995). *The orchids of Victoria* (1st ed.). Carlton, Vic.: Miegunyah Press. [ISBN](/source/ISBN_(identifier)) [052284393X](https://en.wikipedia.org/wiki/Special:BookSources/052284393X).

1. ^ [***a***](#cite_ref-Pridgeon_6-0) [***b***](#cite_ref-Pridgeon_6-1) [***c***](#cite_ref-Pridgeon_6-2) [***d***](#cite_ref-Pridgeon_6-3) Pridgeon, Alec M.; Cribb, Phillip J.; Chase, Mark W.; Rasmussen, Finn, eds. (2001). *Genera Orchidacearum (Volume 2), Orchidoideae (part 1)*. Oxford, England: Oxford University Press. pp. 68–70. [ISBN](/source/ISBN_(identifier)) [0198507100](https://en.wikipedia.org/wiki/Special:BookSources/0198507100).

1. **[^](#cite_ref-RBGS_7-0)** ["*Acianthus*"](http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&search=yes&namesearch=Acianthus&dist=). Royal Botanic Gardens Sydney: plantnet. Retrieved 9 June 2016.

1. ^ [***a***](#cite_ref-efloraSA_8-0) [***b***](#cite_ref-efloraSA_8-1) ["*Acianthus*"](http://www.flora.sa.gov.au/cgi-bin/speciesfacts_display.cgi?form=speciesfacts&family=&genus=Acianthus&species=&iname=&submit=Display). Government of South Australia: efloraSA. Retrieved 9 June 2016.

1. ^ [***a***](#cite_ref-ANBG_9-0) [***b***](#cite_ref-ANBG_9-1) [***c***](#cite_ref-ANBG_9-2) ["*Acianthus*"](https://www.anbg.gov.au/cpbr/cd-keys/orchidkey/html/genera/Acianthus.htm). Australian National Botanic Gardens. Retrieved 12 June 2016.

1. **[^](#cite_ref-APNI_10-0)** ["*Acianthus*"](https://id.biodiversity.org.au/instance/apni/485113). APNI. Retrieved 16 September 2019.

1. **[^](#cite_ref-Brown_11-0)** Brown, Robert (1810). [*Prodromus Florae Novae Hollandiae*](https://www.biodiversitylibrary.org/item/21771#page/191/mode/1up). London. pp. 321–322. Retrieved 9 June 2016.

1. **[^](#cite_ref-Quattrocchi_12-0)** Quattrocchi, Umberto (2000). *CRC world dictionary of plant names : common names, scientific names, eponyms, synonyms, and etymology (Volume 1)*. CRC Press. p. 30. [ISBN](/source/ISBN_(identifier)) [0849326737](https://en.wikipedia.org/wiki/Special:BookSources/0849326737).

1. ^ [***a***](#cite_ref-NZPCN_13-0) [***b***](#cite_ref-NZPCN_13-1) [***c***](#cite_ref-NZPCN_13-2) ["*Acianthus sinclairii*"](https://www.nzpcn.org.nz/flora/species/acianthus-sinclairii/). New Zealand Plant Conservation Network. Retrieved 12 March 2022.

1. **[^](#cite_ref-APClist_14-0)** ["*Acianthus* R.Br"](https://biodiversity.org.au/nsl/services/search/taxonomy?product=APC&tree.id=51209179&name=Acianthus&inc._scientific=&inc.scientific=on&inc._cultivar=&max=100&display=apc&search=true). Australian Plants Census. Retrieved 12 March 2022.

1. **[^](#cite_ref-powo1_15-0)** ["*Acianthus fornicatus*"](https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:614677-1). Plants of the World Online. Retrieved 3 April 2025.

1. **[^](#cite_ref-Jones(2)_16-0)** Jones, David L. (2006). *A complete guide to native orchids of Australia including the island territories*. Frenchs Forest, N.S.W.: New Holland. p. 301. [ISBN](/source/ISBN_(identifier)) [1-877069-12-4](https://en.wikipedia.org/wiki/Special:BookSources/1-877069-12-4).

## External links

- Media related to [Acianthus](https://commons.wikimedia.org/wiki/Acianthus) at Wikimedia Commons

Taxon identifiers Acianthus Wikidata: Q20948 Wikispecies: Acianthus APNI: 73143 BOLD: 412286 CoL: 8VT75 eFloraSA: Acianthus EoL: 17830 FoAO2: Acianthus GBIF: 2800735 GRIN: 89 iNaturalist: 202580 IPNI: 28588-1 IRMNG: 1325788 NCBI: 78688 NZOR: 001eac38-28aa-4b04-89d8-55d9d4e8215c Open Tree of Life: 209843 POWO: urn:lsid:ipni.org:names:28588-1 Tropicos: 40030735 VicFlora: 24516bbe-27a4-4e57-84d6-4db56a4ddc0a WFO: wfo-4000000273

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Adapted from the Wikipedia article [Acianthus](https://en.wikipedia.org/wiki/Acianthus) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Acianthus?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.