Melaleuca

Melaleuca (/ˌmɛləˈljuːkə/) is a genus of nearly 300 species of plants in the myrtle family, Myrtaceae, commonly known as paperbarks, honey-myrtles or tea-trees (although the last name is also applied to species of Leptospermum). They range in size from small shrubs that rarely grow to more than 1 m (3 ft) high, to trees up to 35 m (100 ft). Their flowers generally occur in groups, forming a “head” or “spike” resembling a brush used for cleaning bottles, containing up to 80 individual flowers. They are superficially like Banksia species, which also have their flowers in a spike, but the structures of individual flowers in the two genera are very different. Second only to members of the family Proteaceae, melaleucas are an important food source for nectarivorous 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 are endemic to Australia, with a few also occurring in Malesia. Seven are endemic to New Caledonia, and one is found only on (Australia's) Lord 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, exotic myrtle rust, and especially draining and clearing of swamps threaten many species. Melaleucas range in size from small shrubs such as M. aspalathoides and M. concinna which rarely grow to more than 1 m (3 ft) high, to trees like M. cajuputi and M. quinquenervia, which can reach 35 m (100 ft). (One specimen of M. cajuputi reached 46m (150 ft) Many, like M. lineariifolia, are known as paperbarks and have bark that can be peeled in thin sheets, whilst about 20% of the genus, including M. bracteata, have hard, rough bark and another 20% have fibrous bark. Every species in the genus is an evergreen, and the leaves vary in size from minute and scale-like (M. micromera) to 270 mm (10 in) long (M. leucadendra). Most have distinct oil glands dotted in the leaves, making the leaves aromatic, especially when crushed. 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 papery bract at its base. Five sepals occur, although these are sometimes fused into a ring of tissue and five petals which are usually small, not showy, and fall off as the flower opens or soon after. The stamens vary greatly in colour, from white to cream or yellow, red, or mauve with their yellow tips (the anthers) contrasting with their 'stalks' (filaments). The fruit are woody, cup-shaped, barrel-shaped, or almost spherical capsules, 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 a bushfire. In tropical areas, seeds are released annually in the wet season. The first known description of a Melaleuca species was written by Rumphius in 1741, in Herbarium amboinense before the present system of naming plants was written. The plant he called Arbor alba is now known as Melaleuca leucadendra. The name Melaleuca was first used by Linnaeus in 1767. Many species previously known as Metrosideros were then placed in Melaleuca. In Australia, Melaleuca is the third most diverse plant genus with up to 300 species. The genus Callistemon was raised by Robert Brown, who noted its similarity to Melaleuca, distinguishing it only on the basis of whether the stamens are free of each other, or joined in bundles. Botanists in the past, including Ferdinand von Mueller and Lyndley Craven have proposed uniting the two genera but the matter is not decided. Evidence from DNA studies suggests that either Callistemon and some other genera be incorporated into Melaleuca or that at least 10 new genera be created from the present genus.