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Pengelly Report

Australian Medicinal Plant
Backhousia citriodora
Andrew Pengelly DBMM ND MHNAA

Family:

Myrtaceae

Common Names:

Lemon-scented Myrtle, Sweet Verbena Tree, Lemon Iron Wood

Origin:

Rainforests of south east Queensland. Cultivated elsewhere as an ornamental.

Description:

Backhousia is a genus of 7 species of small to medium sized trees found in the moist forests of Queensland and New South Wales coast, characterised by opposite, shiny and strongly aromatic leaves. They produce dry indehiscent fruit which splits into two chambers upon ripening.

B. citriodora - a medium sized tree with lanceolate, strong lemon-scented leaves. In early summer the tree is covered with clusters of tiny white four petalled flowers. The tree prefers a moist climate and is frost sensitive. Propagation is by cuttings taken in spring.

Constituents:

The leaves contain between 0.33 - 0.86 % essential oil consisting almost entirely of citral.
Penfold and Morrison described a second distinct physiological form of B. citriodora, botanically identical but chemically different. In the second form the oil consists mostly of laevo-citronellal, widely used in the production of perfumes and insect repellents. This oil is chemically almost identical to the oil of Eucalyptus citriodora .

Properties of Essential Oil:

Citral is an aliphatic aldehyde in the monoterpenoid class. In plants such as lemon grass ( Cymbopogon ) and lemon balm ( Melissa officinalis ) citral occurs as two isomeric aldehydes, neral and geraniol.

Citral has been shown to exhibit sedative, anti-viral and anti-fungal properties. Aldehydes, and particularly citral, have long been considered to contain anti-tumor properties, though the few studies carried out are inconclusive.

The germicidal properties were measured using the Ridley-Walker test devised by Penfold and Grant, in which the RW co-efficient of citral is a high 19.5 (ie. 19.5 times the power of phenol) though lower than that of thymol. The pure oil of Backhousia citriodora has a co-efficient of 16, considerably higher than that of Eucalyptus and tea tree oils.

In a study carried out in the 1950's a number of Australian aromatic plants were tested for anti-bacterial action against human pathogens such as Staph. aureus and Staph. typhi. Whilst 15 out of 34 oils passed the test, the most potent of these were Backhousia citriodora and B. angustifolia.

Therapeutics:

Actions: Antiseptic, anti-viral, calmative, sedative and corrective.
Indications: Common cold, influenza, bronchitis, indigestion and other irritable GIT disorders, herpes simplex - apply oil or tincture topically.

Preparation and Dosage:

Standard infusion - 3 cups daily.
Tincture - 1:5 in 45% alcohol. Dose: 2-4ml. Note: Can be dispensed freely as a taste corrective.

Toxicity:

None reported.

Citral is known to cause skin sensitisation in some people. However Tisserand has demonstrated that the oil of lemon-grass, containing up to 85% citral, produced no skin sensitivity. Presumable the same is true for oil of Backhousia and even more certainly in the case of teas and tinctures.

Other species:

B. myrtifolia . B. augutifolia . B. anisata

Conclusion:


For those of us who prefer not to depend on capsules and tablets when dispensing herbal medicines, taste and patient compliance is always a potential problem, and we are constantly trying to devise ways of improving the taste of herbal mixtures. I have found the addition of Backhousia citriodora to both teas and extract/tincture compounds not only vastly improves the flavour but also provides anti-microbial and possible immuno-stimulating benefits, so helpful during the winter months.


Source: Australian Journal of Medical Herbalism Vol 3 (3) 1991. Excerpt on Other Species and References can be found in the full journal article.