Melaleuca is a genus of around 170 species in the Myrtle family (Myrtaceae). However, there are many unnamed and incorrectly named species and the true number is probably well in excess of 200. The majority of species are endemic to Australia but several occur to the north (eg. Indonesia, New Guinea, New Caledonia, Malaysia). The first plants of the genus were, in fact, collected in the mid 1600s in Indonesia by George Runf, a Dutch merchant. These two species are now known as M.leucadendra and M.cajuputi and both also occur in tropical Australia.
Melaleucas are commonly known as "Paperbarks" in the tree forms and "Honey Myrtles" in the smaller forms. These names refer to the flaky bark of many species and the nectar produced in the flowers. The term "Tea Tree" is also applied occasionally by this is more commonly used with the related genus Leptospermum.
The botanical name for the genus means "black and white" and presumably refers to the blackened lower bark and white upper bark of some species, resulting from fire.
Melaleuca is closely related to Callistemon ("Bottlebrushes") and differs from that genus in the way that the stamens are connected to the floral tube. The stamens are generally free in Callistemon but united into bundles in Melaleuca (see also "Melaleuca and Callistemon; Why are they Different?").
In nature, melaleucas are often found along watercourses or along the edges of swamps. They are generally plants of open forest, woodland or shrubland and are popular for gardens and landscaping both in Australia and overseas. With one exception, melaleucas have not become weeds outside of their natural habitat. M.quinquenervia, however, a large tree from eastern Australia, has become a serious pest in the Florida everglades in the USA. This particular species is widely used as a landscaping plant in many parts of Australia.
The showy parts of the flowers of Melaleuca are the stamens, the petals being small and inconspicuous. The stamens are often brightly coloured with red, pink, mauve, purple and yellow being common. The Melaleuca "flower" is really an inflorescence formed by a cluster of small flowers.
Peak flowering for most species is spring (September to November in Australia), however, a spasmodic flowering at other times is not unusual. The flower clusters may occur terminally at the ends of branches or in short spikes along the branches.
Following flowering, three-celled woody seed capsules develop with each capsule containing many small seeds. The seed pods usually remain tightly closed unless stimulated to open by fire or by the death of the plant.
Most melaleucas are small to medium shrubs but a few can become medium to large sized trees.
Very few species of Melaleuca have commercial uses. The timber of M.leucadendra and M.quinquenervia been used for fairly minor applications such as railway sleepers, fence posts and mine props and these species are also useful in honey production.
The most significant use of the genus is in the production of Tea Tree Oil. M.alternifolia is most commonly used species and there has been significant expansion of the industry in the past decade or so. Tea Tree Oil is particularly valuable as a germicide and is used in a number of products including shampoos, antiseptic creams and soaps.