EUCALYPTUS (Myrtaceae)

Eucalyptus is a species of nearly 600 evergreen trees in the Myrtaceae family, almost all native to Australia. A small handful are native to southern New Guinea and southeastern Indonesia and one is native to northern New Guinea and the southern Philippines. Eucalypts come in a huge variety of sizes from mere bush-sized to trees of several hundred feet. Though most are single-trunked, a number are multi-trunked. Rather than shedding their leaves annually, many eucalyptus trees shed their bark annually. Eucalyptus viminalis (common names: manna gum, ribbon gum or white gum) sheds ribbons of bark from its upper branches. This tree is a favored food of the koala.

Eucalypts have abundant flowers during flowering season, some more showy than others. For some, flowering season is spring; for most it is summer and I even found a fall-flowering eucalypt. Though most flowers are white, some species are yellow, pink or red. Ironically, the largest trees have the smallest flowers. The flowers are rich in nectar and are sought after by honeybees. The name eucalyptus comes from the Greek word eucalyptos, which means "well-covered", referring to the coverage of flowers. The fruit is a woody capsule which litters the ground beneath the tree when it drops. Between the bark and the seed capsules, the eucalypt can be a rather messy tree.

The leaves are often long and narrow, some even sickle-shaped. They generally hang vertically, thereby providing only partial shade. The familiar rounded leaves of eucalyptus sprays from craft stores are actually juvenile leaves, specifically the juvenile leaves of Eucapyptus cinerea, according to one source. Though there is a silver dollar eucalyptus (E. polyanthemos), even its adult leaves elongate just a bit and become a bit pointed. They are not the fully round leaves of the juvenile plant. The blue gum, which I’ll discuss more in the medicinal section, also has shorter, squatter leaves than the most typical eucalypts as does the native Philippine gum (E. deglupta). But for the most part, long and narrow is the general leaf description. Though eucalyptus trees are associated with their camphor-scented leaves, there are also leaves of other scents. There is a lemon-scented eucalyptus; there are also several peppermint-scented eucalypts. One of my books, which is hardly comprehensive, listed three different peppermints (E. elata, E. nicholii and E. nova-anglia).

One-hundred-twelve eucalypts have been split off into a new genus, Corymbia. These include the ghost gum (formerly Eucalyptus aparrarinja, now Corymbia aparrarinja), considered by many the archetypal eucalyptus, and the lemon-scented eucalyptus I grew this summer (Corymbia citriodora, formerly Eucalyptus citriodora).
Growing conditions for eucalypts vary with each variety of tree. Soil and climate preferences can vary widely. Most grow fairly easily from seed, but once germinated, the ease of successfully keeping them alive varies widely. The seeds can be quite small. The trees are generally fast growers. Suffice it to say for our purposes that none will grow in Illinois and none will survive long in a container. They are water hogs, but once established are quite drought tolerant. A point of interest is that, like the walnut, the roots of eucalyptus secrete a poisonous chemical which inhibits the growth of nearby plants.

Due to the high oil content in the leaves, fires can spread quite rapidly amongst trees. Sometimes you’ll read about really bad bush fires (i.e., forest fires) in Australia. These are largely fed by eucalypts.

Medicinally, eucalyptus was first used by the Australian aborigines. Unfortunately, due to killings of those people by Europeans and imported diseases, most of the traditional herbal medicinal knowledge of the aborigines was lost. Elders died and tribes were dispersed. What is known is that eucalyptus (E. globulus) leaves were crushed and inhaled to treat common illnesses such as the flu and other respiratory diseases. Decoctions were made from hot water and drunk or applied to the skin. Eucalyptus was thought to cure fevers and infections and it was used to bind wounds.
And, in fact, the aborigines were absolutely correct. Research has shown that the essential oil from the leaves has both an antiseptic and fungicidal effect as well as the ability to dilate the bronchioles of the lungs. In addition, we know that eucalyptus is an expectorant and an anti-viral as well as a warming agent for the skin with a slight anesthetic. It can also be used for pain relief for aching and stiff rheumatic joints, neuralgia and some bacterial skin infections. It is used to treat pulmonary tuberculosis, burns, and is useful for mucus membrane inflammation of the nose and throat. Animal experiments have demonstrated its usefulness in relieving coughs. An infusion or tincture of the leaves can be used as a gargle. It lowers blood sugar levels. Eucalyptus is used in aromatherapy and perfumes. We are most familiar with its use in things such as cough drops and vaporizer inhalent medication and Vicks VapoRub and similar cold medications used to treat congestion.

The essential oil extracted from the leaves and terminal twigs or the balsamic/camphor-scented leaves themselves are the parts of the tree used medicinally. The key constituents of the essential oil are volatile oil, of which cineole makes up to 80%, flavonoids, tannins and resin. The dried leaves can be crushed and put into capsules or used to make tinctures or infusions. The essential oil can be diluted and used as a chest rub. CAUTION: do not take the essential oil internally without professional medical supervision; it can lead to poisoning if misused. Never give internally to small children or infants and do not even use the oil on their faces as this can lead to an asthma-like attack or even death by asphyxiation. Eucalyptus also should not be used by anyone with liver disease.
Although there are hundreds of varieties of eucalyptus trees, it is the blue gum, or Eucalyptus globulus, that is used for medicinal purposes. It is native to Australia and Tasmania. Eucalyptus smithii, which seems to be lesser known, is also valued for its essential oil and is used medicinally and for aromatherapy.

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