Melaleuca

For other uses, see Melaleuca (disambiguation).

Melaleuca
M. armillaris foliage and flowers
Scientific classification
Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Order:	Myrtales
Family:	Myrtaceae
Subfamily:	Myrtoideae
Tribe:	Melaleuceae
Genus:	Melaleuca L. nom. cons.
Species
Over 200; see List of Melaleuca species
Synonyms
Cajuputi Adans. Callistemon R.Br. Gymnagathis Schauer Kajuputi Adans. Meladendron St.-Lag. Melaleucon St.-Lag. Melanoleuca >St.-Lag. Myrtoleucodendron Kuntze

Melaleuca (pron.: /ˌmɛləˈljuːkə/) is a genus of plants in the myrtle family Myrtaceae known for its natural soothing and cleansing properties. There are well over 200 recognised species, most of which are endemic to Australia. A few species occur in Malesia and 7 species are endemic to New Caledonia.

Setting

The species are shrubs and trees growing (depending on species) to 2–30 m (6.6–98 ft) tall, often with flaky, exfoliating bark. The leaves are evergreen, alternately arranged, ovate to lanceolate, 1–25 cm (0.39–9.8 in) long and 0.5–7 cm (0.20–2.8 in) broad, with an entire margin, dark green to grey-green in colour. The flowers are produced in dense clusters along the stems, each flower with fine small petals and a tight bundle of stamens; flower colour varies from white to pink, red, pale yellow or greenish. The fruit is a small capsule containing numerous minute seeds.

Melaleuca is closely related to the genus Callistemon; the main difference between the two is that the stamens are generally free in Callistemon but grouped into bundles in Melaleuca. Callistemon was recently placed into Melaleuca.

In the wild, Melaleuca plants are generally found in open forest, woodland or shrubland, particularly along watercourses and the edges of swamps.

The best-accepted common name for Melaleuca is simply melaleuca; however most of the larger species are also known as tea tree, and the smaller types as honey myrtles, while those species in which the bark is shed in flat, flexible sheets are referred to as paperbarks. The Tea tree is presumably named for the brown colouration of many water courses caused by leaves shed from trees of this and similar species (for a famous example see Brown Lake (Stradbroke Island)). The name "tea tree" is also used for a related genus, Leptospermum, also in Myrtaceae.

One well-known melaleuca, M. alternifolia, is notable for its essential oil which is both anti-fungal and antibiotic, while safely usable for topical applications. This is produced on a commercial scale and marketed as Tea Tree Oil.

In Australia, Melaleuca species are sometimes used as food plants by the larvae of hepialid moths of the genus Aenetus including A. ligniveren. These burrow horizontally into the trunk, then vertically down.

Melaleucas are popular garden plants, both in Australia and other tropical areas worldwide. In Hawaii and the Florida Everglades, M. quinquenervia (Broad-leaved Paperbark) was introduced to help drain low-lying swampy areas. It has since gone on to become a serious invasive species with potentially very serious consequences because the plants are highly flammable and spread aggressively. Melaleuca populations have nearly quadrupled in southern Florida over the past decade, as can be noted on IFAS's SRFer Mapserver

Uses

Traditional Aboriginal uses

Australian Aborigines have used the leaves for many medicinal purposes, including chewing the young leaves to alleviate headache and for other ailments.

Modern uses

Scientific studies have shown that tea tree oil made from M. alternifolia is a highly effective topical antibacterial and antifungal, although it may be toxic when ingested internally in large doses or by children. In rare cases, topical products can be absorbed by the skin and result in toxicity.^{[citation needed]}

The oils of Melaleuca can be found in organic solutions of medication that claims to eliminate warts, including the Human papillomavirus. No scientific evidence proves this claim.

Melaleuca oils are the active ingredient in Burn-Aid, a popular minor burn first aid treatment (an offshoot of the brandname Band-Aid).

M. leucadendra oil, cajeput tree, is also used in many pet fish remedies such as Melafix and Bettafix to treat bacterial and fungal infections. Bettafix is a lighter dilution of cajeput tree oil, while Melafix is a stronger dilution. It is most commonly used to promote fin and tissue regrowth. The remedies are often associated with Betta fish (Siamese Fighting Fish) but are also used with other fish.

Melaleuca bark is used to make a natural bio-degradable paper or papyrus which is considered by many to be a renewable resource and therefore much more environmentally friendly than modern paper farming or deforestation.^{[citation needed]}

Invasive species in Florida

The species M. quinquenervia was introduced to Florida in the United States in the mid-1880s to assist in drying out swampy land and as a garden plant. It formed dense thickets and displaced native vegetation on 391,000 acres (1,580 km²) of wet pine flatwoods, sawgrass marshes, and cypress swamps in the southern part of the state. It is prohibited by DEP and listed as a noxious weed by FDACS.

As an invasive species, M. quinquenervia raised serious environmental issues in Florida's Everglades and damaged the surrounding economy. Agricultural Research Service (ARS) scientists from the Australian Biological Control Laboratory suggested releasing biological controls in the form of insects that feed on this species. In 1997 a weevil (Oxyops vitiosa) was released. It feeds on leaves and flower buds. The University of Florida reports that seed production has been reduced by about 50 percent "on trees they attack." Boreioglycaspis melaleucae (melaleuca psyllid) is also being released.

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  A paperbark in Melbourne

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  Melaleuca quinquenervia bark showing the papery exfoliation from which the common name 'paperbark' derives

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  Paperbark trees in Tasmania after sunset

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  19th century illustration of Melaleuca leucadendra

See also

• List of Melaleuca species
• Poliopaschia lithochlora, a proposed agent for eradication

Further reading

• Hammer KA et al. (2003). "Antifungal activity of the components of Melaleuca alternifolia (tea tree) oil". J. Appl. Microbiol. 95 (4): 853–860. doi:10.1046/j.1365-2672.2003.02059.x. PMID 12969301. 
• Hammer KA et al. (2003). "Susceptibility of oral bacteria to Melaleuca alternifolia (tea tree) oil in vitro". Oral Microbiol. Immunol. 18 (6): 389–392. doi:10.1046/j.0902-0055.2003.00105.x. PMID 14622345. 
• Mondello F et al. (2003). "In vitro and in vivo activity of tea tree oil against azole-susceptible and -resistant human pathogenic yeasts". J. Antimicrob. Chemother. 51 (5): 1223–1229. doi:10.1093/jac/dkg202. PMID 12668571. 
• Oliva B et al. (2003). "Antimycotic activity of Melaleuca alternifolia essential oil and its major components". Lett. Appl. Microbiol. 37 (2): 185–187. doi:10.1046/j.1472-765X.2003.01375.x. PMID 12859665. 
• Takarada K et al. (2004). "A comparison of the antibacterial efficacies of essential oils against oral pathogens". Oral Microbiol. Immunol. 19 (1): 61–64. doi:10.1046/j.0902-0055.2003.00111.x. PMID 14678476. 

External links

• Melaleuca - Australian Native Plants Society (Australia)
• Melaleuca at IFAS