Eucalyptus robusta, commonly known as Swamp Mahogany or Swamp Messmate is a tree native to eastern Australia. It grows in swampy or waterlogged soils, up to 20 to 30 m high. It belongs to Family Myrtaceae.

Eucalyptus robusta grows as a tree to around 20–30 metres with a trunk up to 1 metre in diameter.

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Eucalyptus robusta planted 100 years ago in the Royal Botanic Garden, Sydney
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Another Eucalyptus robusta planted 100 years ago in the Royal Botanic Garden, Sydney
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Another Eucalyptus robusta planted 100 years ago in the Royal Botanic Garden, Sydney


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The trunk and branches are covered with thick red-brown bark, which has a spongy feel and is stringy. The bark on the upper branches peel off in longitudinal strips.

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The thick red-brown bark has a spongy feel and is stringy
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Another image of the bark

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

The adult leaves are broad-lanceolate in shape and arranged alternately along the stems. They measure 10 to 15 cm long by 2.5 to 4.5 cm wide.


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Broad-lanceolate shape leaves of about 10 to 12 cm long


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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

The white or cream flowers are commonly clustered in inflorescences of 7 to 13 flowers. In Sydney the flowers appear any time from March to September, and peak over May and June.

The flower bud measure 2 cm by 0.8 cm wide. It has an operculum (bud cap) with as prominent long beak,[making it fusiform (spindle-shaped).

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The flower buds in groups of 8 or more


P1450326 - Copy (706x1024)The flower bud with the operculum (bud cap) detached showing the green style and white filaments of the coiled up stamens

P1450330 - Copy (1024x981)The stamens and the upper part of the hypanthium (base)

P1450331 (939x1024)The flower bud has been cut vertically open to show the coiled up stamens with the anthers facing towards the ovary

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 3 carpels (3-locular ovary).

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The conspicuous part of the flowers are the white filaments of the stamens. The style is green in colour. Two flower buds with opercula (bud caps) are on the left hand side of the image.
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The underside of the flowers showing the hypanthia and short pedicels
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The stamens of the flower with the style near the right edge of the image.
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The ovary has been cut open to show the three carpels with ovules inside.


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The development of the flower bud to flower and finally to fruit


The fruit is cylindrical, 10–18 mm long, 6–11 mm in diameter; valves are very slightly lower than rim-level. Most of the fruits are 3-locular but some may be 4-locular.

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The fruit of the previous year. Fruit is globose or hemispherical, commonly 3 locular.
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The fruit on the left may be 4 locular but 3 locular are more common.


The koalas (Phascalarctos cinereus) eats the leaves. Eucalyptus robusta appears to be one of several key species of eucalypt for the koala. The grey-headed flying fox (Pteropus poliocephalus) eats the flowers. The musk lorikeet feeds on the nectar of the blossoms.

Eucalyptus robusta  generally grows on heavy clay soils, but is also found on sandy clay and alluvial sand soils.  It adapts well to cultivation, though it often grows too large for home gardens. It is used as a street tree.

The heartwood is extremely durable and resists marine borers. It is used as a round timber for construction of wharves and fencing. The wood is light reddish brown in colour and coarse-textured.

Eucalyptus robusta is widely grown from equatorial to temperate regions, tolerating a wide range of climates and conditions. It has been widely grown in plantations outside Australia, including Argentina, Brazil, Chile, China, Colombia, etc.