Eucalyptus leucoxylon commonly known as Blue Gum, White Ironbark or Yellow Gum belongs to Family Myrtaceae. This species is a small to medium-sized tree, endemic to Australia. It is widely distributed on plains and nearby mountain ranges of NSW, Victoria or coastal South Australia. In NSW this species is known as the Blue Gum and in Victoria it is known as the Yellow Gum. This species I studied was Eucalyptus leucoxylon subsp. megalocarpa.

A street tree in a Sydney suburb. The tree is just about 6 m high.
A street tree in a Sydney suburb. The tree is just about 6 m high.

The upper part sheds irregularly in short ribbons or flakes, leaving a smooth, white, yellow or bluish colour.

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The bark of the lower part of the stem is rough, flaky and fibrous.
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The bark in the upper part of the stem is shedding irregularly in short ribbons or flakes.
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After the dark brown bark has peeled off, the grey coloured trunk is exposed

 

Adult leaves are lanceolate (ie with the widest point at one-third or one-quarter of the leaf from the base, and tapering toward the apex), 8–15 cm long, 1–1.8 cm wide, green or grey-green. The leaves have numerous green and yellow island oil glands of varying sizes.

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Adult leaves are lanceolate

 

Leaf venation and oil glands in a fresh leaf viewed with transmitted light. The yellow white structure in the middle is the midrib.
Leaf venation and oil glands in a fresh leaf viewed with transmitted light. The yellow white structure in the middle is the midrib.
Details of the above image.
Details of the above image.

 

Red, pink or white flowers appear from mid autumn (March in Sydney).

The conspicuous part of the red flowers is mainly the red filament of the stamens. Instead of having petals and sepals, a flower has an hypanthium (base) in green colour and an operculum (lid) also in green. (The hypanthium and the operculum have similar originds as both petals and sepals combined.)

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The two flower buds on the left still have their opercula (bud caps). The operculum is conical in shape.  Below the operculum is the hypanthium. (The plant has been severely infected with plant disease.)

 

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The flower bud has been sagitally cut into halves. The operculum is still partially attached onto the flower bud. The stamens are coiled up in an orderly manner.
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Similar stage as the above. The green part is the style and the top end is the stigma. The stamens are coiled up in an orderly fashion before the flower opens.

 

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The flower buds are commonly found in groups of 3
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Flowers are commonly found in groups of 3.

 

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The showy part of the flower is the red filaments of the stamens. The outer ones do not have anthers; they are known as staminodes. The inner ones are fertile with anthers. The stigma in the middle is green in colour.

 

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The fertile stamens with red filaments and yellow anthers
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The stigma (top yellow green structure) and the style
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The ovary has been cut vertically open to show the ovules.
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The transverse section of the ovary showing 6 carpels inside.
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The same transverse section as above but viewed with transmitted light from below.

 

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The development of the flower bud to the fruit

Fruit is globose or hemispherical, commonly 6 locular, 8–10 mm long, 8–10 mm diameter.

Fruit globose or hemispherical, commonly 6 locular, 8–10 mm long, 8–10 mm diameter
The fruit is globose or hemispherical, commonly 6 locular.

 

Eucalyptus leucoxylon is regularly planted for windbreaks, shade, honey production and for ornamental purposes.

The leaves are distilled for the production of cineole based eucalyptus oil which is used as a flavouring at low levels (0.002%) in various products, including baked goods, confectionery, meat products and beverages. It is toxic if ingested at higher than normal doses.

 

Acknowledgements

I would like to thank Mr Andrew Orme of the National Herbarium of New South Wales for his help in identifying the tree.

 

Bibliography

https://en.wikipedia.org/wiki/Eucalyptus_leucoxylon

http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Eucalyptus~leucoxylon

http://anpsa.org.au/e-leu.html

 

 

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