The more than 600 species of eucalyptus are native to Australia and eastern Indonesia. With heights of up to 100 meters, some species of the evergreen and mostly fast-growing trees are among the largest on earth. The blue-green, leathery leaves are still ovate on young trees, later forming crescent-shaped, drooping forms. The feathery flowers are protected by a tight lid before they bloom, hence the name: in Greek, "eu" means good and "kalyptos" means hidden.

Europeans discovered the tree genus Eucalyptus in Tasmania in 1792. It was not until the middle of the 19th century that eucalyptus oil was extracted and marketed. Before that, people took advantage of the fact that the water-hungry tree dries out its habitat to a depth of 20 meters; in many countries of the world, plantations served to drain swamps. Today, eucalyptus plantations, mostly established for timber production, are also planted in agricultural regions, where they cause major problems for neighbors because of the lowering of the groundwater table.

The alkaloids contained in the eucalyptus leaves make them inedible for animals; only the koala gets by on this diet. However, the leaves also contain up to 3.5 percent essential oil; medicinally, mainly the oil of the blue eucalyptus, Eucalyptus globulus, is used, but the oils of about 50 other species and their mixtures can also be found in the trade. Eucalyptus oil has disinfectant (antimicrobial and fungicidal), anti-inflammatory and mild antispasmodic effects. Its main ingredient is the expectorant cineole, formerly called eucalyptol.