Over 700 species of aromatic, oily, trees or shrubs. Bark is smooth, stringy or a checkered pattern. Most species are heterophyllous (having different kinds of leaves on the same plant) showing differences in seedling, juvenile, intermediate and adult phases. Sometimes the later phases are not achieved. Adult leaves are usually alternate and pendulous, glabrous, petioled, rarely opposite and sessile (without a petiole), but in many species the leaves in the juvenile phase are opposite and sessile. Flowers are white, yellow or red, usually 3 or more in axillary clusters (umbles), calyx and petals fussed into a lip or cap (operculum) and separating from the calyx-tube at anthesis; stamens numerous. Fruit a capsule, opening at the top by 3-6 valves. Native to Australia, Malesia and the Philippines.
Eucalyptus: Greek eu, well, and kalytos, covered, a reference to the lid of the flower.