Eucalyptus is native to Australia, where over 750 species grow wild across nearly every part of the continent. From tropical Queensland to the cooler forests of Tasmania, eucalyptus trees, shrubs, and low-growing forms called mallees dominate the Australian landscape like no other plant genus. While a handful of species are also native to nearby islands in Southeast Asia, Australia is overwhelmingly where eucalyptus comes from, both in terms of evolutionary origin and present-day diversity.
Native Range Across Australia
Eucalyptus doesn’t stick to one corner of Australia. It grows in every state, with the largest concentration in Queensland, where eucalypt woodlands cover more than 294,000 square kilometers. In southeastern Australia, temperate eucalypt woodlands form a nearly continuous belt along the inland side of the Great Dividing Range, stretching from southern Queensland down through New South Wales and into South Australia. In Tasmania, eucalypt woodlands mix with grasslands and forests throughout the northeast and into the Midlands. Western Australia has its own widespread eucalypt populations, often forming a patchwork with heathlands and salt lakes.
This range covers an enormous variety of climates and soils, which is part of why so many species evolved. Some eucalyptus trees tower above 80 meters in wet mountain forests. Others are squat, multi-stemmed mallees barely a few meters tall in arid scrubland. All of them belong to the myrtle family (Myrtaceae), sharing that group with cloves, guava, and allspice.
Ancient Origins on Gondwana
Eucalyptus is far older than Australia’s current geography. The oldest known eucalyptus fossil, a piece of preserved wood, was found in central India and dates to roughly 65 to 70 million years ago, near the end of the age of dinosaurs. At that time, India, Australia, South America, Africa, and Antarctica were still connected or recently separated pieces of the ancient supercontinent Gondwana. Eucalyptus fossils have turned up on several of these former Gondwanan landmasses, suggesting the genus first evolved when these continents still shared land connections and a common pool of plant life.
As the continents drifted apart, eucalyptus found its greatest success in Australia, where it diversified into the hundreds of species we see today. The combination of poor soils, seasonal drought, and frequent fire created conditions that eucalyptus was uniquely suited to exploit.
Built to Survive Fire
One reason eucalyptus dominates Australia is its extraordinary relationship with fire. Most eucalyptus species carry hidden buds beneath their bark, called epicormic buds, that stay dormant until the tree is damaged. After even a high-intensity crown fire that strips every leaf, these buds activate and push out new shoots. Within less than a year, a burned eucalyptus forest can be well on its way to recovering a full canopy.
Some species also develop a swollen, woody root structure called a lignotuber, which stores energy and sprouts new stems if the trunk above is destroyed. This means the tree doesn’t lose its massive investment in woody growth after a fire. It simply regrows from its existing framework, outpacing other plants that have to start from seed. In a landscape where fire has been a regular force for millions of years, this gives eucalyptus an enormous competitive edge.
Why Koalas Depend on It
Eucalyptus leaves are tough, low in nutrition, and loaded with compounds that are toxic to most animals. Koalas are one of the few mammals that eat them almost exclusively, and even koalas are selective. Research on wild koala populations shows they strongly prefer certain species, like ribbon gum (Eucalyptus viminalis), over less digestible options like messmate (Eucalyptus obliqua).
Koalas manage this difficult diet through specialized gut bacteria. Those eating ribbon gum host communities dominated by bacteria with enzymes that break down a variety of plant sugars. Koalas eating messmate, which contains more tannins and tough fiber, carry different bacterial populations geared toward breaking down cellulose. Some gut bacteria in koalas may also play a role in degrading the toxic compounds that make eucalyptus leaves inedible to other animals. This tight relationship between koalas, their gut microbes, and specific eucalyptus species means that losing particular eucalyptus habitats doesn’t just reduce food supply in general: it can eliminate the specific diet a local koala population has adapted to.
How Eucalyptus Spread Around the World
Eucalyptus stayed confined to Australia and nearby islands for millions of years. That changed rapidly in the 1800s, when European colonists began shipping seeds to other continents. In California, the first eucalyptus seeds arrived in 1853, brought by a clipper ship captain named Robert Waterman who had his former first mate carry back a bag of blue gum seeds from Australia. For the first couple of decades, Californians planted eucalyptus mainly as ornamental trees.
That shifted around 1870, when concerns about depleted native timber and fuelwood supplies led the California State Agricultural Society to offer cash premiums for large-scale tree planting. Eucalyptus became the favorite because it grew fast, was believed to have medicinal properties, and was thought to be fireproof. Farmers saw it as a tree that could provide fuel, timber, and profit in a short time, with the disadvantages not yet understood. South America saw a similar boom, with eucalyptus planted by the thousands across the continent.
Today, eucalyptus plantations cover millions of hectares in Brazil, China, India, Portugal, and parts of Africa, grown primarily for paper pulp, construction timber, and essential oil production. Brazil operates some of the world’s largest eucalyptus pulp mills, and the tree has become one of the most widely planted hardwoods on Earth.
Problems in Non-Native Regions
In places where eucalyptus was introduced, it often behaves very differently than it does at home. Without the insects, fungi, and competing plants that keep it in check in Australia, certain species spread aggressively into native ecosystems.
South Africa offers a well-documented case. River red gum (Eucalyptus camaldulensis) is the most aggressively invasive eucalypt there, having transformed long stretches of rivers. In the Cape Floristic Region, one of the world’s biodiversity hotspots, 46% of rivers are invaded by river red gum. Flooded gum (Eucalyptus grandis) and spider gum (Eucalyptus lehmannii) are also established invaders. South African law now lists several eucalyptus species as invasive, requiring regulation and management.
Water consumption is another concern. Seedling studies comparing eucalyptus clones to a native tropical tree found that eucalyptus consumed roughly three to five times more water daily, with the difference closely tied to their larger total leaf area. In water-scarce regions, large eucalyptus plantations can lower water tables and reduce stream flow, affecting both native vegetation and human water supplies. Clearing efforts in South Africa now prioritize removing eucalyptus from riverbanks and nature reserves, where its water use and shade have the most damaging effects on native species.