| Melaleuca | |
|---|---|
 | |
| Melaleuca armillaris foliage and flowers | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Myrtales |
| Family: | Myrtaceae |
| Subfamily: | Myrtoideae |
| Tribe: | Melaleuceae |
| Genus: | Melaleuca L.[1] |
| Species | |
| Synonyms[1] | |
Genus synonymy
| |
Melaleuca (/ˌmɛləˈljuːkə/) is agenus of nearly 300species ofplants in the myrtlefamily,Myrtaceae, commonly known aspaperbarks,honey-myrtles,bottlebrushes ortea-trees (although the last name is also applied to species ofLeptospermum).[2]: 19 They range in size from small shrubs that rarely grow to more than 16 m (52 ft) high, to trees up to 35 m (115 ft). Their flowers generally occur in groups, forming a "head" or "spike" resembling abrush used for cleaning bottles, containing up to 80 individual flowers.
Melaleucas are an important food source fornectarivorous insects, birds, and mammals. Many are popular garden plants, either for their attractive flowers or as dense screens and a few have economic value for producing fencing and oils such as"tea tree" oil. Most melaleucas areendemic toAustralia, with a few also occurring inMalesia. Seven are endemic toNew Caledonia, and one is found only on Australia'sLord Howe Island.
Melaleucas are found in a wide variety of habitats. Many are adapted for life in swamps and boggy places, while others thrive in the poorest of sandy soils or on the edge of saltpans. Some have a wide distribution and are common, whilst others are rare and endangered. Land clearing, exoticmyrtle rust, and especially draining and clearing of swamps threaten many species.
Melaleucas range in size from small shrubs such asM. aspalathoides andM. concinna which rarely grow to more than 1 m (3 ft 3 in) high, to trees likeM. cajuputi andM. quinquenervia, which can reach 35 m (115 ft). (One specimen ofM. cajuputi reached a height of 46 m (151 ft).)[3]
Many, likeM. lineariifolia, are known as paperbarks and have bark that can be peeled in thin sheets, whilst about 20% of the genus, includingM. bracteata, have hard, rough bark and another 20% have fibrous bark. All areevergreen, and the leaves vary in size from minute and scale-like (M. micromera) to 270 mm (11 in) long (M. leucadendra). Most have distinct oil glands dotted in the leaves, making the leaves aromatic, especially when crushed.[2]: 20–21
Melaleuca flowers are usually arranged in spikes or heads. Within the head or spike, the flowers are often in groups of two or three, each flower or group having a paperybract at its base. Fivesepals occur, although these are sometimes fused into a ring of tissue and fivepetals which are usually small, not showy, and fall off as the flower opens or soon after. Thestamens vary greatly in colour, from white to cream or yellow, red, or mauve with their yellow tips (theanthers) contrasting with their "stalks" (filaments).[2]: 20–21
The fruits are woody, cup-shaped, barrel-shaped, or almost sphericalcapsules, often arranged in clusters along the stems. The seeds are sometimes retained in the fruit for many years, only opening when the plant, or part of it, dies or is heated in abushfire. In tropical areas, seeds are released annually in thewet season.[2]: 25–26
The nameMelaleuca is derived from theAncient Greek μέλας (mélas) meaning "dark" or "black" and λευκός (leukós) meaning "white",[4][5] apparently because one of the first specimens described had fire-blackened white bark.[6] The common name "tea tree" has been applied to species in the generaLeptospermum,Melaleuca,Kunzea, andBaeckea because the sailors on theEndeavour used the leaves of a shrub from one of these groups as a replacement for tea (Camellia sinensis) during CaptainJames Cook's 1770 voyage to Australia.[7]
The first known description of aMelaleuca species was written byRumphius in 1741, inHerbarium amboinense[8] before the present system of naming plants was written. The plant he calledArbor alba is now known asMelaleuca leucadendra. The nameMelaleuca was first used byLinnaeus in 1767.[9] Many species previously known asMetrosideros were then placed inMelaleuca. In Australia,Melaleuca is the third most diverse plant genus with up to 300 species.[10]
The genusCallistemon was raised byRobert Brown, who noted its similarity toMelaleuca, distinguishing it only on the basis of whether the stamens are free of each other, or joined in bundles.[11] Botanists in the past, includingFerdinand von Mueller andLyndley Craven[12] have proposed uniting the two genera but the matter is not decided. Evidence from DNA studies suggests that eitherCallistemon and some other genera be incorporated intoMelaleuca or that at least 10 new genera be created from the present genus.[2]: 16–17 [13][14]
In 2014,Lyndley Craven and others proposed, on the basis of DNA evidence and a lack of morphological support,[14] that species in the generaBeaufortia,Calothamnus,Conothamnus,Eremaea,Lamarchea,Petraeomyrtus,Phymatocarpus andRegelia be transferred toMelaleuca.[15] TheWorld Checklist of Selected Plant Families maintained by theRoyal Botanic Gardens, Kew listsCalothamnus and the other genera as synonyms of the accepted genusMelaleuca.[16] The move has not been adopted by all Australianherbaria with some taxonomists, includingAlex George opposing the move.[17]
Most melaleucas occur naturally only on the Australian mainland. Eight occur inTasmania, but only two are endemic to that island. One (M. howeana) is endemic toLord Howe Island and seven are endemic toGrande Terre, the main island of New Caledonia.[18] A few tropical species also occur inPapua New Guinea, and the distribution of one subspecies,Melaleuca cajuputi subsp.cumingiana extends as far north asMyanmar,Thailand, andVietnam. The southwest ofWestern Australia has the greatest density of species, and in the tropical north of the continent, species such asM. argentea andM. leucadendra are the dominant species over large areas.
Melaleucas grow in a range of soil types and many tolerate occasional or even permanent waterlogging. Some species, especially the South Australian swamp paperbark,M. halmaturorum, thrive in saline soils where few other species survive. Many are fire tolerant, regenerating fromepicormic buds or bycoppicing, but no melaleucas occur in rainforest and few species occur in the arid zone.[2]: 26–31
Melaleucas are mostly pollinated by insects, including the introduced honey bee (Apis mellifera), flies, beetles, wasps andthrips. Birds such aslorikeets andhoneyeaters as well asbats often visit the flowers and are probably also pollinators.[2]: 23 [19]
Some species ofMelaleuca, especiallyM. alternifolia, are cultivated for the production of tea tree oil, and in plantations are susceptible to a number of insect pests. The most significant of these is thechrysomelidParopsisterna tigrina, but otherbeetles,cutworm caterpillars (Agrotis species),psyllids, mole crickets (Gryllotalpa), and others cause significant damage. More than 100 species of insects are known to feed on melaleucas. Native stands have fewer predators, but tea treesawfly (Pterygophorus species) andlongicorn beetles are often found.[20] The scale insectBeesonia ferrugineus forms round, fluffy-looking galls on branches of severalMelaleuca species.[21]
Melaleucas are also susceptible to myrtle rust (Puccinia psidii) which can result in damage to soft plant material and the death of highly susceptible hosts. Myrtle rust is common in eastern Australia, includingTasmania and has been detected in theTiwi Islands.[22]
Melaleuca quinquenervia (broad-leaved paperbark) is the most damaging of 60 exotic species introduced to theFloridaEverglades to help drain low-lying swampy areas. Introduced in the early 20th century, it has become a seriousinvasive species, with damaging effects including the displacement of native species, reduction in wildlife habitat, alteration of hydrology, modification of soil, and changes in fire regimes.[23][24][25] The tree's perseverance in the face of efforts to eradicate it has earned it the nickname "punktree".[26]
Aboriginal Australians used several species ofMelaleuca to make rafts, as roofing for shelter, bandages, and food preparation.[27] "Bee bread" and honey were collected from the hives of nativestingless bees in melaleuca forests in theNorthern Territory.[28] TheBundjalung people traditionally lived in the area of north-easternNew South Wales whereMelaleuca alternifolia isendemic, and they treated skin infections by crushing the leaves of that species over skin infections then covering the area with a warm mudpack.[29]
Melaleuca alternifolia is notable for itsessential oil.[30][31] Though it is safe fortopical applications,[32] tea tree oil is toxic if ingested orally.[30]
The oil is produced on a commercial scale and marketed astea tree oil.[33]Melaleuca cajuputi is used to produce a similar oil, known ascajuput oil, which is used inSoutheast Asia to treat a variety of infections and to add fragrance to food and soaps.[34]
Melaleucas are popular garden plants, both in Australia and other tropical areas worldwide. The first to be cultivated were grown in England from seed in 1771. Some melaleucas are commonly cultivated, grown as trees for parks and large gardens (such asMelaleuca leucadendra)[35] or as ornamentals (sometimes asCallistemon) such asM. citrina (Callistemon citrinus),M. hypericifolia andM. wilsonii.[36]
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Tea trees (spelledTi-Trees) are specifically mentioned in the lyrics of a short aria 'Joy' published around 1916 by J.D.Fletcher & Co of London, by Australian composerArthur Chanter (1866-1950).[37]
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