Eucalyptus, a genus of about 600 species of evergreen trees and shrubs native mainly to Australia and Tasmania. Many of the trees are valued for their wood, for the aromatic oil distilled from their leaves, and for the resinous gum that oozes from their bark.

“Eucalyptus,” from the Greek word for “covered,” refers to the lidlike bud covering, shaped like a cone or hemisphere, that falls off when the flowers open. The flowers have no petals, but bristle with many long, often colorful stamens. The fruits are capsules, containing many tiny seeds. The leaves are generally slender and lance- or sickle-shaped. They turn their edges to the sun, thus reducing loss of moisture in the hot tropical and subtropical climates in which the trees grow.

Most eucalyptus trees grow rapidly and become quite tall—some species grow more than 300 feet (90 m) in height. Eucalyptus trees are widely planted as ornamentals and many are cultivated as valuable timber trees, their fast growth making them a quick source of wood. About 90 species are grown in California. Among them is the blue gum, the eucalyptus tree most admired as an ornamental.

The eucalyptus most prized for its wood is the jarrah tree. Its durable wood resists fire and ship worms. It is used to build boats and piers, and for furniture, flooring, interior trim, general construction, paving blocks, telephone poles, wheels, pulleys, and tool handles. The wood of many other species is similarly used. The wood of some kinds is so heavy that it sinks in water.

In its natural state eucalyptus oil is toxic to most mammals. Distilled eucalyptus oil is used mainly in cough drops and medicines to soothe the nose and throat. Eucalyptol, a compound prepared from the oil, is used as an antiseptic. The leaves of the black peppermint are richest in oil. Those of the lemon-scented gum furnish an oil used in making perfumes. Botany Bay kino, a resinous gum, is obtained from wounds in the bark of many species. It is used in astringents and in tanning. The bark of several species is used in tanning.

The genus Eucalyptus belongs to the myrtle family, Myrtaceae. Jarrah is E. marginata; black peppermint, E. amygdalina; lemon-scented gum, E. citricdora; blue gum, E. globulus.