Eucalyptus L'Héritier 1789 is a diverse genus of flowering trees and shrubs in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia, and include Eucalyptus regnans, the tallest known flowering plant on Earth. There are more than 700 species of eucalyptus and most are native to Australia; a very small number are found in adjacent areas of New Guinea and Indonesia. One species, Eucalyptus deglupta, ranges as far north as the Philippines. Of the 15 species found outside Australia, just nine are exclusively non-Australian. Species of eucalyptus are cultivated widely in the tropical and temperate world, including the Americas, Europe, Africa, the Mediterranean Basin, the Middle East, China, and the Indian subcontinent. However, the range over which many eucalypts can be planted in the temperate zone is constrained by their limited cold tolerance. Australia is covered by 92,000,000 hectares of eucalypt forest, comprising three quarters of the area covered by native forest.
Eucalyptus is one of three similar genera that are commonly referred to as "eucalypts", the others being Corymbia and Angophora.