This fascicle deals with the family Myrtaceae, a large family with about 127 genera and 3850 species in the tropics to warm temperate regions of both Old and New Worlds; particularly well represented in Australia. The two native genera with about 21 species are of extreme taxonomic difficulty; in addition a large number of species is cultivated including between 100-150 species of Eucalyptus. Genera which contain widely cultivated species or species which have become naturalised are dealt with in this fascicle. All are included in the key to genera. Cultivated species belonging to genera dealt with in the main text will be found there.