Is a Eucalyptus Tree the Same As a Gum Tree?

Anyone who has visited California has likely seen them: the eucalyptus trees that populate the landscape from Big Sur down to San Diego. While eucalyptus trees are a type of gum tree, not all gum trees are eucalyptus trees — it depends on whether plants are in the ‌Eucalyptus‌ genus or another genus, such as ‌Corymbia‌ and ‌Tristaniopsis‌, that determines this. While they are beautiful and fragrant trees, some eucalyptus species are invasive, often with adverse effects on the surrounding environment.

A gum tree is the common name given to a number of trees that are part of the Myrtle family (Myrtaceae). They're called "gum trees" because of the thick sap that oozes out of the trunk and stems when they sustain any sort of damage.

Many gum trees are indigenous to Australia, and they grow in many places in the United States and elsewhere because the seeds were brought by immigrants in the middle part of the 19th century. Australians leaving Oceania in search of a better life in the New World were aware of the important value that lumber and wood had in general. From building to operating ovens to keeping trains running, wood was critical to all parts of survival. It was a century of wood power.

For these reasons, many Australians traveled to California with seeds of eucalyptus trees. By the same token, much of California was low, marshy, and shrubby scrubland. Settlers who had come from the East were accustomed to the environments afforded by dense, heavily forested areas and wanted to create a similar feel in California. This is how the creation of forests in the area began, most notably the eucalyptus trees on the Berkeley campus that were designed as a windbreak for athletes.

The lemon-scented gum tree (‌Corymbia citriodora‌, zones 8-10) is a gum tree that's known for emitting a strong lemon scent, which can be used successfully as an insect repellent. It is native to northeastern Australia.

The red flowering gum tree (‌Corymbia ficifolia‌, zones 9-10) is also native to Australia and has an unusual red blossom with stamens but no petals. It's a very popular gum tree for use in landscaping and decorating since the boughs are fairly low to the ground and the red blossoms are such a striking color.

The water gum (‌Tristaniopsis laurina‌, zones 10-12) is so-named because of its affinity for growing alongside streams and rivers. This characteristic makes it a good choice for growing in landscapes that have poorly draining soils.

Perhaps the most common eucalyptus species, which most people recognize from branches for sale in flower shops and at farmers' markets, is the silver dollar tree (‌Eucalyptus cinerea‌, zones 7b-11). This southeastern Australia native has branches that are exceptionally fragrant and refreshing. The tree grows very quickly and can survive in cooler areas as well.

The rainbow gum tree (‌Eucalyptus deglupta‌, zones 9-11) is unique both for its appearance and its provenance. One of the few species that is indigenous to lands below the equator, the rainbow gum tree is native to the Philippines and Papua New Guinea. The rainbow gum tree gets its name from its bark, which has colors that vary in shade from green to red.

The manna gum tree (‌Eucalyptus viminalis‌, zones 9-10) is a species that is immediately identifiable by its bark, which peels off in strips. These trees can grow up to 100 feet tall and are one of the few species of gum trees that can actually tolerate cooler climates.

The blue gum tree (‌Eucalyptus globulus‌, zones 9-10) is one of the most commonly planted of all gum trees everywhere around the world. It is so popular in the Oceania region that the Eucalyptus is actually the state flower of Tasmania.

While some people love these trees for their fragrant branches and their beautiful bark, many people aren't so fond of the blue gum tree. It's an invasive plant in many areas, particularly in California. It's invasive because it has escaped cultivation and has grown wild. This has allowed it to move in on the territory that other native plants typically enjoyed, and the blue gum's tall stature creates a situation where it actually shades out other plant species.

Another problem with the blue gum tree is that the boughs break easily and can be dangerous to people walking under them. They also grow too large for smaller lots and often need to be trimmed, which is costly and a hassle. Finally, the oils in the blue gum are very pungent and are considered to be a fire hazard. This can be exceptionally difficult in places like southern California where they are at high risk for forest fires and uncontained burning that leads to wildfires.

Because blue gum trees tend to grow in clusters, the risk of fire is very high. If one tree catches fire, the fire quickly spreads and can be disastrous. For this reason, the spread of eucalyptus growth is problematic for dry regions like southern California. It is also a problem in parts of northern California where deadly and destructive wildfires are common.

Beyond the use of their fragrant foliage and blossoms, the shade they provide and their natural beauty, gum trees have a number of other remarkable qualities that make them unique. For one thing, no flowers on a gum tree have petals. Where other flowers have petals, gum tree blossoms have thousands of different stamens, allowing the tree to self-pollinate when necessary, which is often because they have very few natural pollinators.

Gum trees in general and eucalyptus trees in particular have unusual, square-shaped stems and a unique growth pattern that makes them very visually appealing. Leaves grow in pairs of two and look almost designed for beautiful symmetry. This makes them very popular in floral and tablescape arrangements.

Eucalyptus grows uncommonly fast in the landscape. Most types of eucalyptus reach full maturity only 10 years after planting, which is highly unusual for a hardwood tree. Eucalyptus wood is used widely in the flooring industry, and the rapid growth of the trees ensures that they are a sustainable choice both in terms of the value of the wood and the fact that using eucalyptus trees is less impactful on the environment.

Eucalyptus branches and leaves contain an oil known as cineole. Cineole is a clear, organic liquid compound with a strong fragrance that is what you smell when you smell something called "eucalyptus." This ingredient that is found in high volume in eucalyptus trees is what protects it from predators. Very few species can ingest cineole. It is toxic to humans in high doses. However, cineole does have anti-bacterial, disinfectant and other sterilization uses that make it a natural choice for healers.

In regions with a high risk of malaria, eucalyptus trees are often planted. Since malaria is transmitted by mosquitoes, generally speaking, a wet area would be deadly. Mosquitoes love standing water, so areas with high populations of mosquitoes put humans at terrible risk. Planting eucalyptus trees helps to ward off mosquitoes because of cineole, making it a valuable resource.