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Corymbia ficifolia (formerly known as Eucalyptus ficifolia) commonly called the red flowering gum or Albany red flowering gum is one of the commonly planted ornamental trees in the broader eucalyptus family.

Corymbia is a genus of about 113 species of trees that were classified as Eucalyptus species until the mid-1990s. It includes the bloodwoodsghost gums and spotted gums. DNA research in the 1990s showed that the Corymbia group is more closely related to Angophora than to Eucalyptus, and are probably best regarded as a separate genus. All three genera – AngophoraCorymbia and Eucalyptus – are closely related, often difficult to tell apart by external features and are still commonly referred to as eucalyptus or gum trees.

Corymbias are readily distinguished as gum trees that form corymb inflorescence. A corymb has irregularly lengthened pedicels (lower pedicles are longer and upper pedicels are shorter) that help form a flat-topped inflorescence.

 

Development of the flower from the bud stage

Corymbia ficifolia flowers very prolifically during summer.

Young flower buds
Young flower buds

The showy part of the flowers are the red filaments of the stamens. Instead of having petals and sepals, a flower has an  hypanthium (base) and an operculum (lid). (The hypanthium and operculum may have similar origins as both petals and sepals combined.) The operculum splits open to release the stamens out. Stamens are male reproductive structures made up of anthers and filaments. The anthers produce pollen grains.

The female reproductive structure is called the pistil. It is made up of the stigma, style and ovary. The stigma receives pollen grains. The male nuclei of the pollen grains transferred through the tissue of the style into the ovary. The ovary comprises of 4 carpels. Each carpel contains numerous ovules.  The male nuclei fertilize the female nuclei in the ovule. The ovule develops into a seed. The ovary becomes a fruit (gum nut).

 

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Flower buds and flowers in full bloom. The flower bud in the middle has its operculum just opened showing some curled-up red stamens
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From right to left: young flower bud, flower buds with the operculum begin to open, flower in full bloom with operculum still stay on the flower

 

flower bud
Diagrams of flower bud and flower

 

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From left to right: young flower bud, flower in fill bloom, flower with most of the stamens withered and lost, a fruit
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Diagram showing the development of a flower bud to a fruit ( right to left)

The structure of the flower

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The flower has many stamens with red coloured filaments and a pistil
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Stamens as seen under a microscope
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The style and the stigma (top structure) as seen under a microscope
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The ovary has been cut longitudinally open to show the carpels with the closely packed ovules inside. The ovules are arranged obliquely instead of vertically with the central axis of the ovary.
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Diagram of the longitudinal section of an ovary

 

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Another ovary cut longitudinally open to show the carpels with the closely packed ovules inside. This confirms that the ovules are arranged obliquely.
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The ovules have been deliberately dislodged from the carpels (by a needle) to show the three dimensional shape of the ovules.
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Another ovary has been cut transversely open to show the 4 carpels with the closely packed ovules inside.
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Diagram of the transverse section of an ovary showing 4 carpels, each carpel with numerous ovules
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Another ovary showing the same appearance
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The ovules have been deliberately dislodged from the carpels (by a needle) to show the three dimensional shape of the ovules.

The development of the fruit

The ovary develops into a fruit. The fruit bears seeds. Seeds are dark brown to black, ellipsoidal with terminal wing.

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Young fruit still in early development
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Mature fruit

Mature fruit is about 40 mm long and 20 mm wide, disc vertically descending, valves 4 (rarely 3), deeply enclosed.

External appearance of the top of the fruit
External appearance of the top of the fruit

 

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The fruit was transversely cut open with a saw to view the interior appearance (4 valves)
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Appearance of the interior structures. (This fruit might not be too healthy. The plant may be a hybrid variety that does not give rise to mature fruit.)

 

The leaves and the stem

The leaves are long and the length is about four times the width. The upper epidermis is apple-green in colour and the lower epidermis is pale apple-green. The midrib is yellow.

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The leaves are long and lanceolate (with the widest point at about one-third of the leaf from the base and tapering toward the apex)
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Leaf venation and oil glands in a fresh leaf viewed with transmitted light. The middle yellow structure is the midrib.

 

The bark of the stem
The bark of the stem is rough, brown to grey-brown

 

Appearance of the whole plant which provided the plant specimens for study

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The plant in a suburban street in Sydney

 

Botanical drawings

unnamed
J Pemberton-Corymbia-ficifolia-Red-Flowering-Gum-Coloured-Pencil2 http://www.botanicalartsocietyaustralia.com/dev/jacqueline-pemberton/

 The above botanical drawing by Miss Jacqueline Pemberton, Dip SBA (dist), accurately and very elegantly depicts the development of the flower buds to fruit. It may not be possible to show all the structures in a single photograph. Artists are able to merge a few images into a single botanical drawing. This is the reason that botanical drawing can never be replaced by photography.

Pembleton drawings with labels
Five arbitrary stages 1 to 5 are overlaid on the botanical drawing to show the development of the flower bud to the fruit.

 

This photos show all the structures from buds to fruit but the presentation is not as good as the botanical drawing above.
This photo shows all the structures from flower buds to fruit but the presentation is not as clear and informative as Miss Pemberton’s botanical drawing above.

 

Eucalyptus_ficifolia
Eucalyptus ficifolia– an Australian definitive stamp issued on November 17, 1982. 3 cents. Designer: Betty Conabere

 

 A Request

There are gaps in my botanical knowledge of the gum trees. Suggestions and guidance are most welcome. Thank you very much in advance.

email: patrick.i.siu@gmail.com

 

Acknowledgements:

I would like to thank Miss Miss Jacqueline Pemberton, Dip SBA (dist), most sincerely for allowing me to use her superb botanical drawing and her kind advice on the topic.

Bibliography

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

https://www.anbg.gov.au/cpbr/cd-keys/euclid3/euclidsample/html/Corymbia_ficifolia.htm

http://www.botanicalartsocietyaustralia.com/dev/jacqueline-pemberton/

 

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