Eucalyptus is a diverse genus of trees (rarely shrubs), the members of which dominate the tree flora of Australia. All eucalypts are evergreen, although some species have deciduous bark. On warm days vapourised eucalyptus oil rises above the bush to create the characteristic distant blue haze of the Australian landscape. Eucalyptus oil is highly flammable (trees have been known to explode) and bush fires can travel easily through the oil-rich air of the tree crowns. Eucalypts exhibit leaf dimorphism. When young, the leaves are opposite and often roundish and occassionally without petiole. When several years old, the leaves become quite slender and with long petiole. Eucalyptus flowers typically vary from white, cream, pink, yellow, or red depending upon the species. The flower petals and stamens are fused into a cap called an operculum — as the flower opens the cap is shed. The flowers appear as a fuzzy, cream-yellow ball of stamens. After flowering, hard, woody seed pods develop and are often key to identifying the plant species. Typically, these seed heads remain on the tree until released by fire or the plant's death.
Medicinal uses: Eucalyptus oil has medicinal properties - the well known Vicks vapo-rub is made out of eucalyptus oil. Traditionally, eucalyptus oil is known to be a good medicine for relieving nasal congestion in cold.