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 Kino from any break in the bark.
Over 700 species of Eucalyptus are known; refer to the List of Eucalyptus species for a comprehensive list of species. Some have diverged from the mainstream of the genus to the extent that they are quite isolated genetically and are able to be recognised by only a few relatively invariant characteristics.
Extensive research has gone into the fossil floras of the Paleocene to Oligocene of South-Eastern Australia, and has failed to uncover a single Eucalyptus specimen.
Eucalypts draw a tremendous amount of water from the soil through the process of transpiration.
Eucalyptus is the most common short fibre source for pulpwood to make pulp.
Eucalyptus oil is readily steam distilled from the leaves and can be used for cleaning and as an industrial solvent, as an antiseptic, for deodorising, and in very small quantities in food supplements, especially sweets, cough drops, toothpaste and decongestants.