Eucalyptus grandis, commonly known as the Flooded Gum or Rose Gum, is a tall tree which can reach up to 50 metres. It belongs to Family Myrtaceae. The species name grandis ‘large’ relates to this tree’s large size. The largest specimens can exceed 75 metres tall.

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An Eucalyptus grandis in Royal Botanic Gardens, Sydney

Eucalyptus grandis is found on coastal areas and sub-coastal ranges. It extends north from near Newcastle in New South Wales to around Bundaberg in Queensland. From there it extends north in scattered disjunct populations, and becomes more common in the wet tropics of northern Queensland. Eucalyptus grandis grows well in deep fertile alluvial loams.

The bark of the tree is dark brown grey, fibrous-flaky. It is only persistent on lower trunk (a few metres only). After the shedding of the bark in short ribbons or flake, the tree trunk and the branches are smooth above, powdery, pale- or blue-grey to white in colour.

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The bark of the lower part of the trunk is dark brown grey, fibrous-flaky
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A close-up image of the bark
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The smooth, powdery, pale- or blue-grey to white tree trunk after shedding the bark
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The leaves and flowers in situ on the tree

I am not supposed to pick fresh specimens from the trees in Royal Botanic Gardens, Sydney and the branches are so high above the ground. I just used the fallen branches with flowers on the ground to study the anatomy. The specimens are not too fresh and the quality of the images may not look good.

The glossy dark green leaves are stalked, lanceolate to broad lanceolate, and paler on their undersides, 10 to 16 cm long and 2–3 cm wide. They are arranged alternately along the branches.

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The green leaves are stalked, lanceolate to broad lanceolate
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The upper leaf shows the paler lower epidermis, and the lower leaf shows the darker upper epidermis

 

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

 

Flower buds are arranged in clusters of 5 to 7 or more (7 to 11 according to literature). They are ovoid to glaucous in shape, 9 – 18 mm long, 4 – 5 mm in diameter. The operculum (bud cap) is conical, as long as wide as the hypanthium (calyx tube).

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The flower buds and the flowers in clusters fallen off from a branch
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A flower bud with the operculum (bud cap) about to detach
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The operculum detached from the flower bud exposing the stamens

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The white flowers appear from mid autumn to late winter (April to August).

The conspicuous part of the flowers are their long creamy white stamens. The flower does not have petals or sepals, instead it has a hypanthium. The ovary commonly has 5 to 6 carpels (5 or 6-locular ovary).

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Two flowers viewed from below showing the hypanthium (base)

 

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A flower in full bloom

 

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After fertilisation the stamen dries up and the ovary starts to develop

 

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Transverse section of the ovary showing 6 carpels

The flowers are followed by small pear- or cone-shaped gum nuts which measure 5–8 mm in length and 4–7 mm across

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The fruit has 6 valves
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Fruit conical to pyriform, disc depressed (not pointing upward), valves exserted (thrust forth or thrust out)

 

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Transverse section of the ovary showing 5 carpels
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The fruit has 5 valves

 

 

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Pear- or cone-shaped gum nuts in clusters

 

Flooded gum is much in demand outside Australia for timber and pulp. It has been extensively planted in South Africa, Brazil, Sri Lanka and many other countries. The timber has a pinkish tinge and is used in joinery, flooring, boat building, panelling and plywood. It has a straight grain, and moderate durability and strength, and is resistant to Lyctus borers. Eucalyptus grandis is a food plant for a few types of beetles and other insects.

The tree is too large for most gardens, but makes an attractive tree for large parks and farms, and can be used in riverbank stabilisation.

 

Bibliography

 

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

https://www.florabank.org.au/lucid/key/Species%20Navigator/Media/Html/Eucalyptus_grandis.htm

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

 

 

 

 

 

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