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Acianthus

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Acianthus
Acianthus exsertus
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
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 of about twelve species of plants in the orchid family, Orchidaceae. Mosquito orchids are terrestrial herbs 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, Australia and New Zealand.

Description

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Orchids in the genus Acianthus are terrestrial, perennial, deciduous, sympodial herbs with a single egg-shaped, heart-shaped or lobed leaf at the base. They have small, roughly spherical, underground tubers from which the flower stems arise. Lacking true roots, they have root-like stolons 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, 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 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 are longer than the petals and usually have a long, thin extension on their end. The dorsal sepal is broader than the lateral ones and sometimes forms a hood over the column. The lateral sepals project forward beneath the labellum and the petals spread widely or curve backwards against the ovary. The labellum is heart-shaped and has a prominent callus. The fruit is a thin-walled, glabrous capsule, containing a large number of winged seeds.[2][4][8][9]

Taxonomy and naming

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The genus was first formally described by Robert Brown in 1810 in Prodromus Florae Novae Hollandiae. He described three species (A. fornicatus, A. exsertus and A. caudatus) but did not nominate a type species.[10][11] Orchids in this genus are closely related to those in the genus Caladenia.[3] Some Australian species included in Acianthus were at one time transferred to Acianthella, but are now accepted in Acianthus.[12][13]

The genus name (Acianthus) is derived from the Greek ake or akis, "a point, needle" and anthos "flower" referring to the pointed perianth and the acuminate floral segments.[14][15]

Species

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The following is a list of Acianthus species accepted by Australian Plant Census as at March 2022, apart from A. sinclairii that is accepted by the New Zealand Plant Conservation Network:[13][15]

Plants of the World Online considers A. apprimus, A. borealis, A. collinus, A. exiguus to be synonyms of A. fornicatus and in addition accepts two further species:[12]

Distribution and habitat

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Of the Australian species of Acianthus, 7 are found in New South Wales, 6 in Queensland, 3 in Victoria and 2 in South Australia. The sole New Zealand example, A. sinclairii occurs on both North and South Islands, as well as on Raoul, Stewart, Chatham and Three Kings Islands.[6][15]

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

Ecology

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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 by fungus gnats from the families Anisopodidae, Sciaridae and Mycetophilidae. Usually only a small percentage of the plants in a colony have flowers. Flies on Acianthus caudatus have been observed to move up the labellum, probing with their proboscis until they reach the nectar, where the up and down "pumping" action of their bodies brings them into contact with the viscidium 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.[2][4][6][9]

Use in horticulture

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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][17]

References

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  1. ^ a b "Acianthus". Australian Plant Census. Retrieved 11 November 2022.
  2. ^ a b c 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 1-877069-12-4.
  3. ^ a b c Hoffman, Noel; Brown, Andrew (1984). Orchids of south-west Australia (2 ed.). Nedlands, W.A.: University of Western Australia Press. p. 189. ISBN 0855642262.
  4. ^ a b c Bishop, Anthony (1996). Field guide to the orchids of New South Wales and Victoria. Sydney: UNSW Press. p. 172. ISBN 086840375X.
  5. ^ Backhouse, Gary; Jeanes, Jeffrey (1995). The orchids of Victoria (1st ed.). Carlton, Vic.: Miegunyah Press. ISBN 052284393X.
  6. ^ a b c d 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 0198507100.
  7. ^ "Acianthus". Royal Botanic Gardens Sydney: plantnet. Retrieved 9 June 2016.
  8. ^ a b "Acianthus". Government of South Australia: efloraSA. Retrieved 9 June 2016.
  9. ^ a b c "Acianthus". Australian National Botanic Gardens. Retrieved 12 June 2016.
  10. ^ "Acianthus". APNI. Retrieved 16 September 2019.
  11. ^ Brown, Robert (1810). Prodromus Florae Novae Hollandiae. London. pp. 321–322. Retrieved 9 June 2016.
  12. ^ a b "Acianthus R.Br." Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 6 December 2023.
  13. ^ a b "Acianthus R.Br". Australian Plants Census. Retrieved 12 March 2022.
  14. ^ Quattrocchi, Umberto (2000). CRC world dictionary of plant names : common names, scientific names, eponyms, synonyms, and etymology (Volume 1). CRC Press. p. 30. ISBN 0849326737.
  15. ^ a b c "Acianthus sinclairii". New Zealand Plant Conservation Network. Retrieved 12 March 2022.
  16. ^ "Stigmatodactylus amplexicaulis". Australian Plant Census. Retrieved 6 March 2023.
  17. ^ 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 1-877069-12-4.
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  • Media related to Acianthus at Wikimedia Commons
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