''Backhousia citriodora'', commonly known as lemon myrtle, lemon scented myrtle or lemon scented ironwood, is a

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

in the family

Myrtaceae Myrtaceae (), the myrtle family, is a family of dicotyledonous plants placed within the order Myrtales. Myrtle, pōhutukawa, bay rum tree, clove, guava, acca (feijoa), allspice, and eucalyptus are some notable members of this group. All ...

. It is native to the subtropical rainforests of central and south-eastern

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, with a natural distribution from Mackay to Brisbane.

Description and ecology

The species can reach in height, but is often smaller. The

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

are

evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional throughout the year. This contrasts with deciduous plants, which lose their foliage completely during the winter or dry season. Consisting of many diffe ...

, opposite,

lanceolate The following terms are used to describe leaf plant morphology, morphology in the description and taxonomy (biology), taxonomy of plants. Leaves may be simple (that is, the leaf blade or 'lamina' is undivided) or compound (that is, the leaf blade ...

, long and broad, glossy green, with an entire margin. The

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

s are creamy-white, in diameter, produced in clusters at the ends of the branches from summer through to autumn. After petal fall, the calyx is persistent. A significant fungal pathogen, myrtle rust ('' Uredo rangelii'') was detected in lemon myrtle plantations in January 2011. Myrtle rust severely damages new growth and threatens lemon myrtle production.

Etymology

Lemon myrtle was given the botanical name ''Backhousia citriodora'' by Ferdinand von Mueller in 1853 after his friend, the English botanist,

James Backhouse :''See alsfor two other James Backhouse botanists and nursery owners of York.'' James Backhouse (8 July 1794 – 20 January 1869) was a botanist and missionary for the Quaker Church body, church in Australia. His son, also James Backhouse (bota ...

. The common name reflects the strong

lemon The lemon (''Citrus'' × ''limon'') is a species of small evergreen tree in the ''Citrus'' genus of the flowering plant family Rutaceae. A true lemon is a hybrid of the citron and the bitter orange. Its origins are uncertain, but some ...

smell of the crushed leaves. 'Lemon scented myrtle' was the primary common name until the shortened trade name, 'lemon myrtle', was created by the native foods industry to market the leaf for culinary use. Lemon myrtle is now the more common name for the plant and its products. Lemon myrtle is sometimes confused with 'lemon ironbark', which is ''

Eucalyptus staigeriana ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often mallees, and a few are shrubs. Along with several other genera in the tribe Eucalypteae, includin ...

''. Other common names are sweet verbena tree, lemon scented verbena (not to be confused with

lemon verbena ''Aloysia citrodora'', lemon verbena, is a species of flowering plant in the verbena family Verbenaceae, native to South America. Other common names include lemon beebrush. It was brought to Europe by the Spanish and the Portuguese in the 17th ...

), and sweet verbena myrtle.

Uses

History

Aboriginal Australians Aboriginal Australians are the various indigenous peoples of the Mainland Australia, Australian mainland and many of its islands, excluding the ethnically distinct people of the Torres Strait Islands. Humans first migrated to Australia (co ...

have long used lemon myrtle, both in cuisine and as a healing plant. The oil has the highest

citral Citral is an acyclic monoterpene aldehyde. Being a monoterpene, it is made of two isoprene units. Citral is a collective term which covers two geometric isomers that have their own separate names; the ''E''-isomer is named geranial (''trans''- ...

purity; typically higher than

lemongrass ''Cymbopogon'', also known as lemongrass, barbed wire grass, silky heads, oily heads, Cochin grass, Malabar grass, citronella grass or fever grass, is a genus of Asian, African, Australian, and tropical island plants in the grass family. Some ...

. It is also considered to have a "cleaner and sweeter" aroma than comparable sources of citral–lemongrass and '' Litsea cubeba''. In 1888, Bertram first isolated the essential oil from ''B. citriodora''. In 1925, it was found to be significantly germicidal, and it was later shown to be antimicrobial. In the 1940s, Tarax was the first company to use ''B. citriodora'' oil as a lemon

flavouring A flavoring (or flavouring), also known as flavor (or flavour) or flavorant, is a food additive that is used to improve the taste or smell of food. It changes the perceptual impression of food as determined primarily by the chemoreceptors of ...

during

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

. In 1989, ''B. citriodora'' was investigated as a potential leaf spice and commercial crop by Peter Hardwick, who commissioned the Wollongbar Agricultural Institute to analyse ''B. citriodora'' selections using

gas chromatography Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for Separation process, separating and analyzing compounds that can be vaporized without Chemical decomposition, decomposition. Typical uses of GC include t ...

. In 2001, a Standards for Oil of ''B. citriodora'' was established by The Essential Oils Unit, Wollongbar, and

Standards Australia Standards Australia is a standards organisation established in 1922 and is recognised through a Memorandum of Understanding (MoU) with the Australian government as the primary non-government standards development body in Australia. It is a co ...

Culinary

CSIRO ScienceImage 4242 Dried and Crushed Lemon Myrtle Leaves Backhousia citriodora

Lemon myrtle is one of the well known

bushfood Bush tucker, also called bush food, is any food native to Australia and historically eaten by Indigenous Australians and Torres Strait Islander peoples, but it can also describe any native flora, fauna, or fungi used for culinary or medicinal ...

flavours and is sometimes referred to as the "Queen of the lemon herbs". The leaf is often used as dried flakes, or in the form of an encapsulated flavour essence for enhanced shelf-life. It has a range of uses, such as lemon myrtle flakes in

shortbread Shortbread or shortie is a traditional Scottish biscuit usually made from one part sugar, white sugar, two parts butter and three to four parts plain flour, plain wheat flour. Shortbread does not contain leavening, such as baking powder or bakin ...

; flavouring in

pasta Pasta (, ; ) is a type of food typically made from an Leavening agent, unleavened dough of wheat flour mixed with water or Eggs as food, eggs, and formed into sheets or other shapes, then cooked by boiling or baking. Pasta was originally on ...

; whole leaf with baked

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

; infused in

macadamia ''Macadamia'' is a genus of four species of trees in the flowering plant family Proteaceae. They are indigenous to Australia—specifically, northeastern New South Wales and central and southeastern Queensland. Two species of the genus are comm ...

or vegetable oils; and made into

tea Tea is an aromatic beverage prepared by pouring hot or boiling water over cured or fresh leaves of '' Camellia sinensis'', an evergreen shrub native to East Asia which probably originated in the borderlands of south-western China and nor ...

, including tea blends. It can also be used as a lemon flavour replacement in

milk Milk is a white liquid food produced by the mammary glands of lactating mammals. It is the primary source of nutrition for young mammals (including breastfeeding, breastfed human infants) before they are able to digestion, digest solid food. ...

-based foods, such as

cheesecake Cheesecake is a dessert made with a soft fresh cheese (typically cottage cheese, cream cheese, quark or ricotta), eggs, and sugar. It may have a crust or base made from crushed cookies (or digestive biscuits), graham crackers, pastry, ...

, lemon flavoured ice-cream and

sorbet Sorbet (, ) is a frozen dessert made using ice combined with fruit juice, fruit purée, or other ingredients, such as wine, liqueur, or honey. Sorbet does not contain dairy products. Sherbet is similar to sorbet, but contains dairy. Etymolog ...

without the curdling problem associated with

fruit

acidity An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the ...

. ''Backhousia citriodora'' has two essential oil

chemotype A chemotype (sometimes chemovar) is a chemically distinct entity in a plant or microorganism, with differences in the composition of the secondary metabolites. Minor genetic and epigenetic changes with little or no effect on morphology or anatomy ...

s. The citral chemotype is more prevalent and is cultivated in Australia for

and

essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...

. Citral as an isolate in steam distilled lemon myrtle oil is typically 90–98%, and oil yield 1–3% from fresh leaf. The citronellal chemotype is uncommon, and can be used as an insect repellent. The dried leaf has

free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabolic disorders Metabolism ...

scavenging ability.

Antimicrobial

Lemon myrtle

possesses

antimicrobial An antimicrobial is an agent that kills microorganisms (microbicide) or stops their growth (bacteriostatic agent). Antimicrobial medicines can be grouped according to the microorganisms they are used to treat. For example, antibiotics are used aga ...

properties; however, the undiluted essential oil is toxic to human cells ''

in vitro ''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...

''. When diluted to approximately 1%, absorption through the skin and subsequent damage is thought to be minimal. Lemon myrtle oil has a high Rideal–Walker coefficient, a measure of antimicrobial potency. Use of lemon myrtle oil as a treatment for skin lesions caused by

molluscum contagiosum virus Molluscum contagiosum virus (MCV) is a species of DNA poxvirus that causes the human skin infection molluscum contagiosum. Molluscum contagiosum affects about 200,000 people a year, about 1% of all diagnosed skin diseases. Diagnosis is based o ...

(MCV), a disease typically affecting children and immuno-compromised patients, has been investigated. Nine of sixteen patients who were treated with 10% strength lemon myrtle oil showed a significant improvement, compared to none in the control group. A study in 2003 which investigated the effectiveness of different preparations of lemon myrtle against bacteria and fungi concluded that the plant had potential as an

antiseptic An antiseptic ( and ) is an antimicrobial substance or compound that is applied to living tissue to reduce the possibility of sepsis, infection, or putrefaction. Antiseptics are generally distinguished from ''antibiotics'' by the latter's abil ...

or as a surface disinfectant, or as an anti-microbial food additive. The oil is a popular ingredient in health care and cleaning products, especially soaps, lotions, skin-whitening preparations and shampoos.

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 and usually has a dense canopy. The principal 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. Lemon myrtle can also be propagated from cutting, but is slow to strike. A study into the plant growing

adventitious roots Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant ...

found that "actively growing axillary buds, wide stems and mature leaves" are good indicators that a cutting will take root successfully and survive. A further study on temperature recommended glasshouses for growing cuttings throughout the year. 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 is important to retain some lower branches when pruning for plant health. The harvested leaves are dried for leaf

spice In the culinary arts, a spice is any seed, fruit, root, Bark (botany), bark, or other plant substance in a form primarily used for flavoring or coloring food. Spices are distinguished from herbs, which are the leaves, flowers, or stems of pl ...

, or distilled for the essential oil. The majority of commercial lemon myrtle is grown in

and the north coast of

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

, Australia. A 2009 study has suggested that drying lemon myrtle leaves at higher temperatures improves the citral content of the dried leaves, but discolours the leaves more.

References

External links

Australian Bushfood and Native Medicine Forum

Broad range of lemon myrtle products and recipes

Lemon Myrtle
from Vic Cherikoff {{Taxonbar, from=Q2708073 citriodora Flora of Queensland Myrtales of Australia Trees of Australia Bushfood Crops originating from Australia Medicinal plants of Australia Essential oils Taxa named by Ferdinand von Mueller