Backhousia citriodora

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Lemon myrtle
Backhousia citriodora, garden specimen, in flower
Backhousia citriodora, garden specimen, in flower
Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Subclass: Rosidae
Order: Myrtales
Family: Myrtaceae
Genus: Backhousia
Species: B. citriodora
Binomial name
Backhousia citriodora
F.Muell.

Backhousia citriodora (Lemon Myrtle, Lemon Scented Myrtle) is a flowering plant in the family Myrtaceae, genus Backhousia, native to subtropical rainforests of eastern Australia. Other common names are Sweet Verbena Tree, Sweet Verbena Myrtle, Lemon scented Verbena, and Lemon scented Backhousia.

It can reach 20 m in height, but is often smaller. The leaves are evergreen, opposite, lanceolate, 5-12 cm long and 1.5-2.5 cm broad, glossy green, with an entire margin. The flowers are creamy-white, 5-7 mm diameter, produced in clusters at the ends of the branches from summer through to autumn, after petal fall the calyx is persistent.

Lemon myrtle was given the botanical name Backhousia citriodora in 1853 after the English botanist, James Backhouse. The common name reflects the strong lemon smell of the crushed leaves.

Lemon myrtle is sometimes confused with "lemon ironbark", which is Eucalyptus staigeriana.

Essential oils

B.citriodora has two essential oil chemotypes:

  • The citral chemotype is more prevalent and is cultivated in Australia for flavouring and essential oil. Citral as an isolate in steam distilled lemon myrtle oil is typically 90-98%, and oil yield 1-3% from fresh leaf. Citral purity is high when compared to other plant-based sources.
  • The citronellal chemotype is uncommon, and can be used as an insect repellant.

Uses

Indigenous Australians have long used lemon myrtle, both in cuisine and as a healing plant. The oil is very high in citral content; typically higher than lemongrass. The leaves of the plant are used in cooking, forming one of the more well-known bushfood flavours. It has an extensive range of uses, such as lemon flavouring in pasta, with fish, infused in macadamia or vegetable oils, and made into tea. It can also be used as a lemon replacement in milk-based foods, such as cheescake, lemon flavoured ice-cream and sorbet that would normally curdle due to lemon's citric acid. The taste/smell is similar to lemon (hence the name), verbena and lemongrass but not at all acidic. During former US President Bill Clinton's visit to Australia in 1996, lemon myrtle tart was the dessert item at the formal reception hosted by the Australian Government. It is often described as "more lemon than lemon".

Lemon myrtle essential oil has also been shown to possess antimicrobial properties; however the undiluted essential oil is toxic to human cells in vitro.[1] When diluted to approximately 1%, absorption through the skin and subsequent damage is thought to be minimal.[2] Use of lemon myrtle oil as a treatment for skin lesions caused by molluscum contagiosum virus (MCV), a disease affecting children and immuno-compromised patients, has been investigated. Nine of sixteen patients who were treated with lemon myrtle oil showed a significant improvement, compared to none in the control group.[3] The oil is a popular ingredient in health care and cleaning products, especially soaps, lotions and shampoos. It is marketed in the capitalized identity of Lemon Myrtle. The majority of commercial lemon myrtle is grown in Queensland and the north coast of New South Wales, Australia.

Cultivation

Lemon myrtle is a cultivated ornamental plant. It can be grown from tropical to warm temperate climates, and may handle cooler districts provided it can be protected from frost when young. In cultivation it rarely exceeds about 5 metres and usually has a dense canopy. The principle attraction to gardeners is the lemon smell which perfumes both the leaves and flowers of the tree. Lemon myrtle is a hardy plant which tolerates all but the poorest drained soils. It can be slow growing but responds well to slow release fertilisers.

Seedling lemon myrtle go through a shrubby, slow juvenile growth stage, before developing a dominant trunk. Growing cuttings from mature trees bypasses the shrubby juvenile stage. Cutting propagation is also used to provide a consistent product in commercial production.

In plantation cultivation the tree is typically maintained as a shrub by regular harvesting from the top and sides. Mechanical harvesting is used in commercial plantations. It's important to retain some lower branches when pruning for plant health. The harvested leaves are dried for leaf spice, or distilled for the essential oil.

Backhousia citriodora development

Pre 1788 - Aboriginal people use B.citriodora for medicine and flavouring.

1888 – Bertram isolates citral from B.citriodora oil.[4], and Messrs. Schimmel and Co., Dresden, write about the essential oil as having “…probably a future.”

1900s-1920s - B.citriodora distilled on a small-scale commercial basis around Eumundi, Queensland.

1920s – Discovery of antimicrobial qualities of steam-distilled B.citriodora oil, by A.R. Penfold and R.Grant, Technological Museum, Sydney.

1940s – Tarax Co. use B.citriodora oil as a lemon flavouring during World War II.

1989 – B.citriodora investigated as a potential spice and commercial crop by Peter Hardwick, Wildnerness Foods Pty Ltd, in cunjunction with gas chromatography analysis of B.citriodora selections by Dr Ian Southwell, The Essential Oils Unit, Wollongbar Agricultural Institute.

1990 – Restaurants and food manufacturers supplied with dried B.citriodora leaf by Vic Cherikoff, Bush Tucker Supply Pty Ltd, produced by Russel and Sharon Costin, Limpinwood Gardens.

1991 – B.citriodora plantation established by Dennis Archer and Rosemary Cullen-Archer, Toona Essential Oils Pty Ltd, ; and subsequent commercial supply of plantation produced B.citriodora oil in 1993.

Mid 1990s – Large-scale plantations of B.citriodora established by Australian Native Lemon Myrtle Ltd.

Late 1990s – B.citriodora begins to be supplied internationally for a range of flavouring, cosmetic and anti-microbial products. Agronomic production of B.citriodora starts to exceed demand.

2004 – Monograph published on B.citriodora by Toona Essential Oils pty Ltd.

References

  • Atkinson W, Brice H. (1955). "Antibacterial substances produced by flowering plants". Aust. J. Exp. Biology. 33: 547–54.
  • APNI Australian Plant Name Index

Footnotes

  1. Hayes AJ, Markovic B. "Toxicity of Australian essential oil Backhousia citriodora (Lemon myrtle). Part 1. Antimicrobial activity and in vitro cytotoxicity." Food Chem Toxicol. 40(4):535-43 (2002). PubMed abstract
  2. Hayes AJ, Markovic B. "Toxicity of Australian essential oil Backhousia citriodora (lemon myrtle). Part 2. Absorption and histopathology following application to human skin." Food Chem Toxicol. 41(10):1409-16 (2003). PubMed abstract
  3. Burke BE, Baillie JE, Olson RD. "Essential oil of Australian lemon myrtle (Backhousia citriodora) in the treatment of molluscum contagiosum in children." Biomed Pharmacother. 58(4):245-7 (2004). PubMed abstract, CATIE summary
  4. Simonsen, J. L. (Second Ed., 1953). The Terpenes, Vol. I. Cambridge University Press. pp. 83–100. Check date values in: |date= (help)

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