'For the use of the colonists, the bark will always afford the best means of distinction.’
Baron Ferdinand von Mueller 1858
In Australia, eucalypts are so ubiquitous that one is rarely in an outdoor space where no eucalypt is visible. With more than 900 species in three closely related genera (Angophora, Corymbia, Eucalyptus), identification is a real challenge to the amateur taxonomist. Hybridisation, variability of taxonomic characteristics, and the sheer difficulty of collecting the critical reproductive parts essential for identification from tall trees —flowers, buds and fruit — presents a formidable challenge.
The best way to begin identification is to use a handbook on local trees. For the Sydney Basin region I can recommend Eucalypts of the Sydney Region by Gary Leonard (UNSW Press, 2007). Soon, however, you will find that some street and garden eucalypt trees are not represented in the local compilations, and may come from anywhere in Australia. Tallowwood and Lemon-scented gums, for example, which are not endemic to the region, have been massively planted around Sydney, and more recently the Western Australian red-flowering gum (Corymbia ficifolia) has become very popular, amongst others. Recently I came across, in inner suburban Annandale, a single street tree example of the sugar gum, Eucalyptus cladocalyx, which is restricted in the wild to three populations in South Australia.
For this reason you will soon need to progress to using the app EUCLID Eucalypts of Australia, an online database and interactive identification key that covers all Australian eucalypts. To use this key effectively, unfortunately, a fair knowledge of botanical terminology is necessary. Euclid will help you build up expertise with its large glossary of terms.
Although it is a lesser character for identification, the bark of eucalypt trees is always available and it may be the only character easily accessible on the first visit. The photographs in the website show some of the range of eucalypt barks. My first contact with a tree is to sample a little of its bark, test it for stringiness, toughness, brittleness, friability, note colour of the outer- and under-bark. Then observe its general appearance—fissured, tessellated, ropy, smooth, sandpaper textured, extent on the trunk and limbs, peeling in plates or ribbons. A fair guess as to the species based on the bark can be confirmed by dropped leaves, buds and fruit that may be available on a subsequent visit to the tree.