Eucalyptus pauciflora, Snow gum

An evergreen from Australia with aromatic foliage, traditionally used for a wide range of inflammatory conditions and infections including coughs and colds.

scientific name Eucalyptus pauciflora Siber. ex Spreng.

family Myrtaceae

alternate names Cabbage gum

parts used Bark and leaves

Eucalyptus plantation near Dartington, UK

Description

The snow gum is an evergreen shrub or small tree growing fast to 12m tall. The bark is smooth, somewhat mottled white or brown due to shedding of strips of bark, and grey-green lanceolate leaves up to 20cm long are borne in pairs.

Habitat

This is a variable species from eastern Australia, which grows in mountainous areas up to 1500m.

Related plants

A closely related variety E. pauciflora subsp. niphophila, also known as the snow gum, is found in higher mountain areas up to 2000m, reported as hardy to USDA zone 7 (UK zone 7). It grows to 6m high. The tall-growing blue gum (E. globulus) and the cider gum (E. gunnii) are the usual sources of aromatic leaves containing an antiseptic essential oil.1 Other sources of essential oil include lemon eucalyptus (E. citriodora), E. polybractea and E. camaldulensis.²

Cultivation and harvest

Cultivation

The snow gum is one of the hardiest kinds of eucalyptus, hardy to USDA zone 8 (UK zone 8), though it is best to avoid frost pockets. A number of UK forestry trials have grown Eucalyptus species for biomass and energy crops, finding that the fastest growing varieties tended to be more susceptible to cold damage, although individuals of both E. gunnii and E. pauciflora varieties were able to survive on challenging sites.³ Eucalyptus trees prefer well-drained soils and can grow in poor soil. Choose the planting site carefully as Eucalyptus species are known for being unlikely to transplant well after several years. Snow gum cannot grow in the shade, and needs a sunny sheltered position. A deep mulch around the roots to prevent water loss and reduce the likelihood of freezing may be helpful. Avoid feeding in windy sites as too much top growth can increase wind rock. Most Eucalyptus species coppice readily, normally being cut in plantation forestry to a maximum height of 12cm with recommendations to be thinned after 9-18 months to three or fewer stems.

Pests and diseases

Snow gum is largely pest- and disease-free unless stressed when it can become subject to fungal attack. Eucalyptus gall wasp can disfigure the leaves according to the Woodland Trust.

Propagation

Seed is surface sown in February/March in a greenhouse. Species that come from high altitudes benefit from 6-8 weeks’ cold stratification at 2^oC (35^oF). Pot up the seedlings into individual pots as soon as the second set of seed leaves has developed. Plant out into their permanent positions in early summer and give them some protection from the cold in their first winter. Cuttings of mature shoots with at least one leaf bud, about 10cm in length, can be taken in June/July and placed in a free-draining medium in a moist environment at 27-32^oC (80-89^oF).

Harvesting

Bark and leaf can be harvested at any time and used fresh or dried for later use.

Snow gum leaves

Therapeutic use

Traditional

In traditional Aboriginal systems, the leaves of Euca­lyptus species could be burned for inhalation, or used in a poultice, while the trees could also provide sap and gum for use in drinks and treating burns, cuts and sores.

Medicinal actions and uses

Eucalyptus essential oil is antiseptic, antibacterial, antispasmodic, expectorant, antiviral and antifungal, and has immune-stimulating and anti-inflammatory effects. Eucalyptus preparations can be used in a range of infectious complaints, particularly in coughs and colds.⁴

Clinical applications and research

The bark and leaves are rich in essential oils used for coughs and colds, with antiseptic effects exerted through direct application to the skin and through inhalation.⁵ An Australian study showed 60% recovery in 50 patients with Tinea species fungal infections using an ointment formulated with essential oil from E. pauciflora.⁶

Sample preparations and dosage

Distillation is the usual process to extract the essential oil. For inhalation use, 12 drops of the essential oil are dropped into boiling hot water in a basin. Alternatively, add 200ml of boiling water to a teaspoon of dried herb, then carefully inhale the steam placing a towel over your head. Dried leaves can be infused in a carrier oil; the oil can then be applied to the skin for treating fungal complaints.

Constituents and commerce

Key constituents

The leaves are rich in tannins, ellagitannins, triterpenes, sesquiterpenes and flavonoids. Essential oil constituents include the monoterpenes 1,8-cineole and α-pinene.⁷ There is much variation in the constituents of essential oils of Eucalyptus species:⁸ though the snow gum is reported to have higher levels of sesquiterpenes than other species.⁹

Commerce

In Australia, E. polybractea shrubs 1m high are harvested at between 18-24 months old. There are large plantations in China. Total world production in 1991 of medicinal eucalyptus essential oil was estimated at 3000 tons.¹⁰ According to a market analysis in 2018, the global eucalyptus oil market will be worth over US$64 million by the end of 2025.¹¹ Eucalyptol or cineole content is the usual marker for medicinal eucalyptus essential oil.

Safety

Eucalyptus essential oil is not for internal use. For external use the essential oil should be diluted in case of skin irritation and use on the face should be avoided. Excessive use of the leaves can cause nausea, vomiting and diarrhoea.

Other uses

Biomass production of fast-growing trees. E. gunnii and E. globulus are cultivated in many subtropical areas including Portugal and Spain, for paper pulp manufacture.¹²

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1 Busia (2016) vol 2, p208.

2 Ferraz Filho AC, Scolforo JBS and Mola-Yudego B. (2014) The coppice-with-standards silvicultural system as applied to Eucalyptus plantations – a review. Journal of Forestry Research 25: 237-248.

3 Leslie A, Mencuccini M and Perks MP. (2011) Eucalyptus in the British Isles. Quarterly Journal of Forestry 105: 43-53.

4 Committee on Herbal Medicinal Products (HMPC). (2013) Community Herbal Monograph on Eucalyptus globulus Labill., folium, London, UK: European Medicines Agency.

5 Sadlon AE and Lamson DW. (2010) Immune-modifying and antimicrobial effects of eucalyptus oil and simple inhalation devices. Altern Med Rev 15: 33-47.

6 Shahi SK, Shukla AC, Bajaj AK, et al. (2000) Broad spectrum herbal therapy against superficial fungal infections. Skin Pharmacol Appl Skin Physiol 13: 60-64.

7 WHO (2004) vol 2.

8 Miguel MG, Gago C, Antunes MD, et al. (2018) Antibacterial, anti-oxidant, and antiproliferative activities of Corymbia citriodora and the essential oils of eight Eucalyptus species. Medicines (Basel) 5: 61.

9 Williams C. (2011) Medicinal Plants in Australia. Volume 2: Gums, Resins, Tannin and Essential Oils, Kenthurst, Australia: Rosenberg Publishing, pp168-169.

10 Ciesla (2002) Non-wood Forest Products from Temperate Broad-leaved Trees, Rome: Food and Agriculture Organisation of the United Nations, p30.

11 Transparency Market Research. Global eucalyptus oil market: Snapshot, www.transparencymarketresearch.com/eucalyptus-oil-market.html (2018, accessed 30 April 2019).

12 WHO (2004) vol 2.