Tea tree oil comes from the evergreen leaves of the Australian Melaleuca alternifolia tree, or tea tree, and has nothing to do with the black or green brew you drink in the mornings. (In fact, tea tree is poisonous when taken internally, so you should never, ever drink it.) Interestingly enough, the tea tree, which can reach heights over 25 feet, does not naturally grow outside of Australia.
The first recorded use of the Aussie oil was in the 1920s, when it was revered as a germ fighter. In fact, Australian soldiers were supposedly encouraged to keep the oil in their military kits during World War II as an antibiotic. It quickly spread to the United Kingdom, Germany, France, Italy, Denmark, Sweden, and other European countries, and these days there are massive plantations across Western Australia, Queensland, and New South Wales growing the product on a large scale. The oil has a slightly astringent and woody scent, and you can find it both as a neat essential oil and as an active component in various topical salves and creams.