Common Name: Lemon-Scented Gum

General Information

Corymbia citriodora is a medium to large, evergreen tree of handsome appearance, with pale grey, cream or pink powdery bark, smooth throughout, decorticating in flakes, and somewhat sparse foliage[]. The tree is often straight stemmed, usually 25 - 40 metres tall with occasional specimens to 50 metres[].
Valued especially for its timber and essential oil, the tree is widely cultivated in many tropical subtropical and warm temperate areas of the world[]. The tree is also often grown as an ornamental in gardens[].

Known Hazards

None known

Botanical References

, ,

Range

Australia - Queensland, northeastern New South Wales.

Habitat

Usually found in heavy soils[], but also succeeding on deep sandy loams in coastal regions[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	45.00 m
Growth Rate	Fast
Pollinators	Bees, Insects
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Corymbia citriodora is native from the tropical climate of eastern Queensland to the subtropical and warm temperate regions of northern New South Wales. It is usually found in areas where the summers are hot (it can withstand a mean monthly maximum of 29 - 35°c) and any winter is generally mild. It is not a very cold-hardy plant, but succeeds in areas where frosts are occasional and generally light. It can succeed in arid to semiarid zones, though is said to grow best where the mean annual rainfall, falling mostly in the summer, is within the range 600 - 1,300mm, with a 5 - 7 month dry season[].
Prefers a sunny position in a moderately fertile well-drained moisture retentive circum-neutral soil[]. Tolerates poor and dry soils, especially those low in mineral elements[].Plants can be grown in infertile clays, laterites, poor and gravelly soils and podzols, preferably well drained[]. Established plants are drought tolerant[]. Does not succeed in frost hollows or in windy sites[].
The plant develops a lignotuber - this is a woody tuber that starts to develop near the base of seedlings and can become massive in the mature plants of some species. It possesses embedded vegetative buds, allowing the plant to regenerate following crown destruction, for example by fire[].
A very fast growing species[]. Flowering usually starts within 2 years after planting and seeds are produced abundantly by 5 years of age[].
This species is often cultivated from warm temperate areas to the tropics for its essential oil; it especially thrives in a Mediterranean climate[, ]. The leaves are strongly lemon-scented when crushed[].
When grown for fuel, yields of 10 - 21 cubic metres per hectare per year have been obtained[].
Whilst most Corymbia species, grown in small numbers outside their native range, can be an attractive and useful addition to the landscape, certain species (including this one) are more problematic. When grown in monocultures, especially outside their native range, they can become an environmental disaster. They are voracious, especially in their use of water; they are allelopathic, inhibiting the growth of the native flora; they reduce habitats for native fauna; and encourage the worst possible attitudes to land use and conservation[].
The trees cast a very light shade[]. Flower buds are formed in the summer prior to flowering and seed capsules need at least a further year in which to ripen[].
Plants are shallow-rooting and, especially in windy areas, should be planted out into their permanent positions when small to ensure that they do not suffer from wind-rock[]. They strongly resent root disturbance and should be container grown before planting out into their permanent position[].
Corymbia species have not adopted a deciduous habit and continue to grow until it is too cold for them to do so. This makes them more susceptible to damage from sudden cold snaps. If temperature fluctuations are more gradual, as in a woodland for example, the plants have the opportunity to stop growing and become dormant, thus making them more cold resistant. A deep mulch around the roots to prevent the soil from freezing also helps the trees to survive cold conditions[]. Many members of this genus are remarkably adaptable however, and there can be a dramatic increase in the hardiness of subsequent generations from the seed of survivors growing in temperate zones[].

Edible Uses

Produces a sweet manna-like substance that is scraped off the leaves and eaten[].

Medicinal

Corymbia leaves are a traditional Aboriginal herbal remedy.

The essential oil found in the leaves is rich in citronellal which is a powerful antiseptic and antibacterial. It is used all over the world for relieving coughs and colds, sore throats and other infections[, ]. The essential oil is a common ingredient in many over-the-counter cold remedies[]. An essential oil obtained from the leaves is antibacterial[]. The essential oil obtained from various species of eucalyptus is a very powerful antiseptic, especially when it is old, because ozone is formed in it on exposure to air. It has a decided disinfectant action, destroying the lower forms of life[]. The oil can be used externally, applied to cuts, skin infections etc, it can also be inhaled for treating blocked nasal passages, it can be gargled for sore throat and can also be taken internally for a wide range of complaints[]. Some caution is advised, however, because like all essential oils, it can have a deleterious effect on the body in larger doses[].

A kino resin is exuded from the tree[]. It can also be obtained from the tree by making incisions in the trunk[, ]. This resin contains citriodorol, which is antibiotic, and tannins which are powerfully astringent. It is used internally in the treatment of diarrhoea and bladder inflammation[, , , ].
Applied externally, the resin is used to treat cuts etc[, ].

Agroforestry Uses:

The flowers are rich in nectar and are a good bee crop[].

Other Uses

A lemon-scented essential oil is obtained from the leaves[, , , ]. It is used, especially in perfumery but also medicinally[, ]. The leaves yield between 0.5 to 2.0% essential oil[]. This species is a very rich source of citronella, which is much used in the perfumery industry[, ]. Some batches of the essential oil contain 98% citronella[]. Glabrous leaves may contain oil with 65.5% citronellal, 12.2% citronella, and 3.6% isopulegol; hairy leaves contain more oil with 86.6- 90.1% citronellal, 4.6 - 6.0% citronella, and 0.7 - 0.8% isopulegol, 1-pinene, b-pinene, and isovaleric aldehyde are also recovered[].
The essential oil from the leaves is used as an ingredient in commercial cosmetic preparations as a masking agent and tonic[].

The leaves and the essential oil are used as an insect repellent[]. The leaves are also an ingredient of potpourri[].

The bark may contain up to 12% tannin[].

The heartwood is pale grey-brown to dark brown; it is demarcated from the up to 60mm wide band of white or cream sapwood. The grain is straight or interlocked and occasionally wavy; the texture open and coarse. The wood is hard, strong and tough. It saws easily, planes well, but is rather difficult to nail and prone to checking and collapsing during drying. The timber is susceptible to marine borer and termite attack It is used for general and heavy construction such as frame and bridge construction, flooring, cladding, tool handles and case manufacturing[, , ].
The wood is used for fuel. The hard heavy wood (sp. grav. 0.75 - 1.1) burns steadily and makes a good charcoal with an ash content of 1 - 2%[].

Propagation

Seed - surface sow late winter/early spring in a sunny position in a greenhouse[, , ]. Species that come from high altitudes appreciate 6 - 8 weeks cold stratification at 2°c[]. Pot up the seedlings into individual pots as soon as the second set of seed leaves has developed, if left longer than this they might not move well. Plant out into their permanent positions in early summer and give them some protection from the cold in their first winter. The seed can also be sown in early summer, the young trees being planted in their final positions in late spring of the following year. The seed has a long viability[].