Eucalyptus globulus

Eucalyptus globulus
E. globulus in Hawaii.
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Myrtales
Family:	Myrtaceae
Genus:	Eucalyptus
Species:	E. globulus
Binomial name
Eucalyptus globulus Labill.

The Tasmanian Blue Gum, Southern Blue Gum or Blue Gum, (Eucalyptus globulus) is an evergreen tree, one of the most widely cultivated trees native to Australia. They typically grow from 30 to 55 m (98 to 180 ft) tall. The tallest currently known specimen in Tasmania is 90.7 m tall.^[1] There are historical claims of even taller trees, the tallest being 101 m (330 ft)^[2]. The natural distribution of the species includes Tasmania and southern Victoria (particularly the Otway Ranges and southern Gippsland). There are also isolated occurrences on King Island and Flinders Island in Bass Strait and on the summit of the You Yangs near Geelong. There are naturalized non-native occurrences in southern Europe (Spain and Portugal), southern Africa, New Zealand, western United States (California), Hawaii and Macaronesia^[3].

The d'Entrecasteaux expedition made immediate use of the species when they discovered it, the timber was used to improve their oared boats.^[4] The Tasmanian Blue Gum was proclaimed as the floral emblem of Tasmania on 27 November 1962. The species name is from the Latin globulus, a little button, referring to the shape of the operculum.

Description

The bark shreds often, peeling in large strips. The broad juvenile leaves are borne in opposite pairs on square stems. They are about 6 to 15 cm long and covered with a blue-grey, waxy bloom, which is the origin of the common name "blue gum". The mature leaves are narrow, sickle-shaped and dark shining green. They are arranged alternately on rounded stems and range from 15 to 35 cm in length. The buds are top-shaped, ribbed and warty and have a flattened operculum (cap on the flower bud) bearing a central knob. The cream-colored flowers are borne singly in the leaf axils and produce copious nectar that yields a strongly flavored honey. The fruits are woody and range from 1.5 to 2.5 cm in diameter. Numerous small seeds are shed through valves (numbering between 3 and 6 per fruit) which open on the top of the fruit. It produces roots throughout the soil profile, rooting several feet deep in some soils. They do not form taproots.

The plant was first described by the French botanist Jacques Labillardière in his publications Relation du Voyage à la Recherche de la Pérouse (1800) and Novae Hollandiae Plantarum Specimen (1804).^[5][6] The author collected specimens at Recherche Bay during the d'Entrecasteaux expedition in 1792.^[4]

Uses

Blue gum is one of the most extensively planted eucalypts. Its rapid growth and adaptability to a range of conditions is responsible for its popularity. It is especially well-suited to countries with a Mediterranean-type climate, but also grows well in high altitudes in the tropics.^[7]

Blue gums have historically been used as street trees but are now regarded as unsuitable by many municipalities due to their rapid growth and mature size.

Timber and fuelwood

Blue gum timber is yellow-brown, fairly heavy, with an interlocked grain, and is difficult to season.^[8] It comprises 65% of all plantation hardwood in Australia with approximately 4,500 km² planted.^[9] The tree is widely cultivated elsewhere in the world. It is primarily planted as a pulpwood, and also as an important fuelwood in many countries. It has poor lumber qualities due to growth stress problems, but can be used in construction, fence posts and poles.^[10]

Essential oil

The leaves are steam distilled to extract eucalyptus oil. E.globulus is the primary source of global eucalyptus oil production, with China being the largest commercial producer.^[11][12] The oil has therapeutic, perfumery, flavoring, antimicrobial and biopesticide properties.^{[13][14][15][16]} Oil yield ranges from 1.0-2.4% (fresh weight), with cineole being the major isolate. E.globulus oil has established itself internationally because it is virtually phellandrene free, a necessary characteristic for internal pharmaceutical use.^[17] In 1870, Cloez, identified and ascribed the name "eucalyptol" — now more often called cineole — to the dominant portion of E. globulus oil.^[18]

Herb tea

Blue gum leaves are used as a therapeutic herbal tea.^[19]

Honey

Blue gum flowers are considered a good source of nectar and pollen for bees.

Environmental weed

It was introduced to California in the mid 1800s, partly in response to the Southern Pacific Railroad's need for timber to make railroad ties, and is prominent in many parks in San Francisco and throughout the state. Some native plant enthusiasts consider it an invasive species due to its ability to quickly spread and displace native plant communities ^[20] but the USDA does not list it among Invasive and Noxious plants in California. Controversial programs are underway to remove all eucalyptus growth and restore native biomes in some park areas, such as on Angel Island in San Francisco Bay.

Related species

Many botanists treat the Tasmanian Blue Gum as a subspecies of a broader species concept. This broader E. globulus includes the following subspecies:

• E. globulus subsp. bicostata = E. bicostata - Southern Blue Gum, Eurabbie, Victorian Blue Gum
• E. globulus subsp. globulus = E. globulus - Tasmanian Blue Gum
• E. globulus subsp. maidenii= E. maidenii - Maiden's Gum
• E. globulus subsp. pseudoglobulus = E. pseudoglobulus - Gippsland Blue Gum, Victorian Eurabbie

The broader E. globulus concept is supported by Royal Botanic Gardens, Melbourne ^[21] and the Tasmanian Herbarium ^[22], but not by Royal Botanic Gardens, Sydney ^[23] where the four taxa are considered distinct species.

References

External links

Wikimedia Commons has media related to: Eucalyptus globulus

Wikispecies has information related to: Eucalyptus globulus

• Botanical characteristics of Eucalyptus globulus
• Australian National Botanic Gardens
• Chronology of the discovery of Eucalyptus globulus Iglesias Trabado, Gustavo (2007). In: EUCALYPTOLOGICS

Shedding bark.	Flower bud.	Fruit.	3, 4, 5 & 6 valved fruits.
An illustration from Köhler's Medicinal Plants (1887).