Eucalyptus is one of three similar genera that are commonly referred to as "eucalypts", the others being Corymbia and Angophora. Many species, but far from all, are known as gum trees because they exude copious sap from any break in the bark (e.g. scribbly gum). The generic name is derived from the Greek words ευ (eu) "well" and καλυπτος (kalyptos) "covered", referring to the operculum on the calyx that initially conceals the flower.
Some eucalyptus species have attracted attention from global development researchers and environmentalists because of desirable traits such as being fast-growing sources of wood, producing oil that can be used for cleaning and as a natural insecticide, or an ability to be used to drain swamps and thereby reduce the risk of malaria. Outside their natural ranges, eucalypts are both lauded for their beneficial economic impact on poor populations and criticised for being "invasive water-suckers", leading to controversy over their total impact.
On warm days eucalyptus forests are sometimes shrouded in a smog-like mist of vaporised volatile organic compounds (terpenoids); the Australian Blue Mountains take their name from the haze.
Read more about Eucalyptus: Species and Hybridism, Related Genera, Tall Timber, Frost Intolerance, Animal Relationships, Adaptation To Fire, Cultivation and Uses, Eucalyptus As An Invasive Species, History