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.