| Blue gum | |
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| Eucalyptus globulus subsp.maidenii | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Myrtales |
| Family: | Myrtaceae |
| Genus: | Eucalyptus |
| Species: | E. globulus |
| Binomial name | |
| Eucalyptus globulus | |
| Synonyms[1] | |
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Eucalyptus globulus, commonly known assouthern blue gum[2] orblue gum, is a species offlowering plant in the familyMyrtaceae. It is a tall,evergreen treeendemic to southeastern Australia. ThisEucalyptus species has mostly smooth bark, juvenile leaves that are whitish and waxy on the lower surface, glossy green, lance-shaped adult leaves,glaucous, ribbed flower buds arranged singly or in groups of three or seven in leafaxils, white flowers and woody fruit.
There are four subspecies, each with a different distribution across Australia, occurring in New South Wales, Victoria and Tasmania. The subspecies are theVictorian blue gum,Tasmanian blue gum,Maiden's gum, andVictorian eurabbie.
Eucalyptus globulus is a tree that typically grows to a height of 45 m (148 ft) but may sometimes only be a stunted shrub, or alternatively under ideal conditions can grow as tall as 90 m (300 ft), and forms alignotuber. The bark is usually smooth, white to cream-coloured but there are sometimes slabs of persistent, unshed bark at the base. Young plants, often several metres tall, andcoppice regrowth have stems that are more or less square in cross-section with a prominent wing on each corner. Juvenile leaves are mostly arranged in opposite pairs,sessile,glaucous elliptic to egg-shaped, up to 150 mm (5.9 in) long and 105 mm (4.1 in) wide. Adult leaves are arranged alternately, the same glossy to dark green on both sides, lance-shaped or curved, 150–300 mm (5.9–11.8 in) long and 17–30 mm (0.67–1.18 in) wide on apetiole 1.5–6 mm (0.059–0.236 in) long. The flower buds are arranged singly or in groups of three or seven in leaf axils, sometimes sessile or on a short thickpeduncle. The individual buds are also usually sessile, sometimes on apedicel up to 5 mm (0.20 in) long. Mature buds are top-shaped to conical, glaucous or green, with a flattened hemispherical, wartyoperculum with a central knob. Flowering time varies with subspecies and distribution but the flowers are always white. The fruit is a woody conical or hemisphericalcapsule 2–3 cm diameter with the valves close to rim level.[2][3][4][5][6][7][8]
Eucalyptus globulus was first formally described in 1800 by the French botanistJacques Labillardière in his book,Relation du Voyage à la Recherche de la Pérouse.[9][10][11] Labillardière collected specimens atRecherche Bay during thed'Entrecasteaux expedition in 1792.[12]
Thed'Entrecasteaux expedition made immediate use of the species when they discovered it, the timber being used to improve their oared boats.[12] The Tasmanian blue gum was proclaimed as thefloral emblem ofTasmania on 27 November 1962. The species name is from theLatinglobulus, a little ball or small sphere,[13] referring to the shape of the fruit.[3]
In 1974,James Barrie Kirkpatrick described four subspecies and the names have been accepted by theAustralian Plant Census.[14] Each subspecies has a characteristic arrangement of its flower buds:[15]
Blue gum grows in forests in New South Wales, Victoria and Tasmania, including some of theBass Strait Islands. The nominate subspeciesE. g. subsp.globulus is mainly found in lowland parts of Tasmania, but is also found on some Bass Strait islands includingKing Island, and in the extreme south-west of Victoria. SubspeciesE. g. subsp.bicostata occurs inmontane and tableland areas between the Carrai Plateau in northern New South Wales and thePyrenees in Victoria. SubspeciesE. g. subsp.maidenii occurs on near-coastal ranges of south-eastern New South Wales and eastern Victoria. SubspeciesE. g. subsp.pseudoglobulus is mostly distributed in easternGippsland but there are isolated populations further inland and in theNadgee Nature Reserve in south-eastern New South Wales.[3]
There arenaturalised non-native occurrences inIreland (where self-sown saplings typically grow 2.5 m per year when young),[20]Spain andPortugal, and other parts of southernEurope includingCyprus andMacaronesia, and in southernAfrica,New Zealand, and the westernUnited States (California,Hawaii).[21]
They typically grow from 30–55 m (98–180 ft) tall. There are historical claims of much taller trees, with Tasmanian D. W. Lewin claiming that the tallest was 101 m (331 ft).[22]
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.[23]
It comprises 65% of allplantationhardwood in Australia with approximately 4,500 km2 (1,100,000 acres) planted.[24]
In about 1860Francis Cook planted the tree on theMonserrate Palace, his property atSintra in Portugal. By 1878 the tree "had spread from one end of Portugal to the other".[25]
E. globulus begun to be planted as plantations inLos Lagos andLos Ríos regions of Chile in the 1990s.[26] However at these latitudes around the40th parallel south the tree is at the southern border of the climatic conditions where it can grow, hence good growth in this part ofsouthern Chile requires good site selection such as sunny north-facing slopes.[26] Some of these plantations grow onred clay soil.[26]
Blue gum timber is yellow-brown, fairly heavy, with an interlocked grain, and is difficult to season.[27] It has poortimber quality due to growth stress problems, but can be used inconstruction, fence posts and poles.[28]
The leaves aresteam distilled to extracteucalyptus oil.E. globulus is the primary source of global eucalyptus oil production, withChina being the largest commercial producer.[29][30] Oil yield ranges from 1.0 to 2.4% (fresh weight), withcineole being the major isolate.E. globulus oil has established itself internationally because it is virtuallyphellandrene free, a necessary characteristic for internalpharmaceutical use.[31] In 1870,Cloez identified and ascribed the name "eucalyptol" — now more often called cineole — to the dominant portion ofE. globulus oil.[32]
TheEuropean Medicines AgencyCommittee on Herbal Medicinal Products concluded thattraditional medicines based on eucalyptus oil can be used for treatingcough associated with thecommon cold, and to relieve symptoms of localized muscle pain.[33] Eucalyptus products appear safe and somewhat effective in reducing cough symptoms fromrespiratory infections, but theclinical significance is unclear and more high-quality studies are needed.[34]
Tasmanian blue gum leaves are used as aherbal tea.[35]
E. globulus bark containsquinic,dihydroxyphenylacetic andcaffeic acids,bis(hexahydroxydiphenoyl (HHDP))-glucose,galloyl-bis(HHDP)-glucose,galloyl-HHDP-glucose,isorhamentin-hexoside,quercetin-hexoside,methylellagic acid (EA)-pentose conjugate,myricetin-rhamnoside,isorhamnetin-rhamnoside,mearnsetin,phloridzin,mearnsetin-hexoside,luteolin and aproanthocyanidin B-type dimer,digalloylglucose andcatechin.[36] The hydrolyzable tanninstellimagrandin I,eucalbanin C,2-O-digalloyl-1,3,4-tri-O-galloyl-β-D-glucose,6-O-digalloyl-1,2,3-tri-O-galloyl-β-D-glucose, as well asgallic acid and (+)-catechin can also be isolated.[37]Tricetin is a rare flavone aglycone found in the pollen of members of the Myrtaceae, subfamilyLeptospermoideae, such asE. globulus.[38]
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