Rainbow Gum: Eucalyptus deglupta

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Point No. 8

 Species: Eucalyptus deglupta Blume

Family: Myrtaceae

 

History at University of Pretoria

This plant was donated by Aquaflora nursery which obtained the seed from Durban Botanical Gardens. It was planted by Jason Sampson and Alpheus Nthite in 2012. The tree is unusual due to its show stopping bark which has strips of multiple colours, much like a rainbow.

 

Description

This incredible genus Eucalyptus was discovered by the French botanist L'Héritier de Brutelle, Charles Louis in 1788. Eucalyptus deglupta was first described by Blume, Carl(Karl) Ludwig von in 1850¹. E. deglupta, commonly known as the Rainbow gum, is one of more than seven hundred Eucalyptus species. Rainbow gum originated from Papua New Guinea with its natural habitat scattered in the Northern hemisphere; it is the only species of Eucalyptus native to the northern half of the globe. While it is cold tolerant, the plant is not tolerant to frost and prefers a wet tropical climate, found in rainforests. In its optimal habitat, the tree can grow 60 meters in height and in other habitats it can reach 30 meters with a 2.4-meter diameter². The tree prefers full sunlight with rich medium to wet soil.

The common name is attributed to the array of colours visible on its bark after three years of growth. The rainbow-like appearance is caused by the shedding of thin layers of bark at different stages. First, neon green bark will appear after shedding.

Over time air exposure will cause a colour change in the tender bark resulting in a purple and blue appearance. Lastly, it will gradually turn to yellow, orange and red hues³. However, the colours will fade towards wintertime leaving plain brown bark again until the shedding cycle begins again.

Another key characteristic used to identify the species is the flowers of Eucalyptus. The flowers are arranged in a branching inflorescence where each branch has groups of seven buds.  The white-to-yellow flowers are unique because they are not made up of mainly petals, but rather of numerous fluffy stamens that are between 2 - 10 mm long¹. The genus name is derived from the Greek language, where ‘eu’ means well and ‘kalypto’ means to cover. The name came from observing the flowers which have united calyx lobes and petals forming a cap that is shed when the flower opens².

 

 

Photo 113589849, (c) Forest and Kim Starr, some rights reserved (CC BY)

The blooming season can occur at any time of the year depending on location. For example, in Indonesia, flowers are present the whole year, but fruits are only produced at the beginning of the rainy season. The mature fruits are brown and semi-circular in shape with 3-4 valves. In each valve 3-12 well-formed seeds are present. The seeds are tiny, brown, and flattened in appearance, containing a small terminal wing that can easily be used to propagate a new tree.

Interesting facts

• E. deglupta is one of the 259 heritage trees of Singapore. Heritage trees are mature individual trees that are selected for protection by law under the Heritage Trees Scheme which was put in place on the 17^th of August in 2001⁴.
• The oil produced by E. deglupta, and its bark are poisonous to animals such as dogs, cats and horses.
• The tree is not only used as an ornamental for its attractive bark but it is also planted in major plantations for pulp production⁵.

Photo 113589848, (c) Thomas, some rights reserved (CC BY-SA)

 

 

Text prepared by Suzanne Gerber and Kayleigh Venter, 2022 BOT 366 class.

 

Cited sources:

1. Orwa, C. et al. (2009) Agroforestree Database: a tree reference and selection guide. Version 4. Available at: https://www.cabdirect.org/cabdirect/abstract/20177200441 (Accessed: 3 November 2022).

 

2. Plant Finder (1999). Eucalyptus deglupta Available at: https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=282890 (Accessed: 3 November 2022).

 

3. Xu, D. (2022)The Colorful Life of the Rainbow Eucalyptus. Available at: https://www.nature.com/scitable/blog/student voices/the_colorful_life_of_the/#:~:text=The%20naturally%20brown%20bark%20drops,%2C%20red%2C%20and%20yellow%20hues. (Accessed: 3 November 2022).

 

4. Parks, N. (2018) Eucalyptus deglupta. Available at: https://www.nparks.gov.sg/FloraFaunaWeb/Flora/2/8/2886#:~:text=Originates%20from%20the%20rain%2Dforests,a%20humid%2C%20cooler%20tropical%20climate. (Accessed: 3 November 2022).

 

Gardens, C. (2022) Eucalyptus deglupta (Rainbow Gum). Available at: https://www.gardenia.net/plant/eucalyptu