Melaleuca

For other uses, see Melaleuca (disambiguation).

Melaleuca

M. armillaris foliage and flowers
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
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^[1]

Melaleuca /ˌmɛləˈljuːkə/ is a genus of plants in the myrtle family Myrtaceae. There are well over 200 recognised species, most of which are endemic to Australia.^[2] A few species occur in Malesia and 7 species are endemic to New Caledonia.^[2]^[3]

Setting

Paperbark trees on the East Alligator River in the Northern Territory, Australia

The species are shrubs and trees growing (depending on species) to 2–30 m (6.6–98.4 ft) tall, often with flaky, exfoliating bark. The leaves are evergreen, alternately arranged, ovate to lanceolate, 1–25 cm (0.39–9.84 in) long and 0.5–7 cm (0.20–2.76 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.^[4]

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 species in 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 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^[5]

Uses

Traditional Aboriginal uses

Aboriginal Australians 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 may have some promise for mild cases of acne and athlete's foot, however there are many health claims made for it that are not backed by medical evidence.

The oils of Melaleuca can be found in organic solutions of medication that claim to eliminate warts, including the human papillomavirus (HPV). No scientific evidence proves these claims.^[6]

Melaleuca oils are the active ingredient in Burn-Aid, a popular minor burn first aid treatment.^[7]

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.

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.^[8]

As an invasive species, M. quinquenervia raised serious environmental issues in Florida's Everglades and damaged the surrounding economy. Agricultural Research Service (ARS) scientists^[9] from the Australian Biological Control Laboratory^[10] suggested releasing biological controls in the form of insects that feed on this species.^[11] 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.^[12]

A paperbark in Melbourne
Melaleuca quinquenervia bark showing the papery exfoliation from which the common name 'paperbark' derives
Paperbark trees in Tasmania after sunset
19th century illustration of Melaleuca leucadendra