Tree profile: Umbrella Thorn

Lab Note #9
Jun 23, 2014
  Umbrella Thorn, the quintessential acacia

Scientific name: Acacia tortilis 
Acacia: from the greek word ‘akis’ meaning a point or a barb;   Tortilis: means twisted, referring to the seed pods
Family: Pod-bearing family (Fabaceae) 
Indigenous names: Haak-en-steek (Afrikaans), Mosu, Moswana (North Sotho), umSasane (Siswati); Nsasani (Tsonga), Muunga-Khanga (Venda)









Without a doubt, when you think of an 'African tree' the umbrella thorn is the tree that instantly comes to mind. The sparse, flat-topped silhouette is an iconic element of the savanna landscape, and its addition to a movie scene is all that's needed to ground you firmly 'somewhere in Africa.' 





If the lion didn't give it away, we are definitely in Africa


Despite its ubiquitous usage in the media, the umbrella thorn is only one species of an extensive genre (Acacias*) that has over 150 members in Africa alone. Nevertheless, it is considered an indicator species of the veld habitat, which characterizes what many people think of when they picture a savanna. It is an incredibly important tree, both economically and ecologically. Its leaves and pods provide excellent fodder for both domestic and wild animals and its wood can be used for fuel and to make furniture. Even more importantly, it is a wonderful shade tree, providing well-needed relief from the African sun. Be careful where you step though! The umbrella thorn, unlike some other acacias, is known for dropping old thorns.




A bush hyrax sampling some nutritious umbrella thorn foliage.  Fact of the day: the hyrax is the closet living relative to the elephant.

In addition to its aesthetic contributions to the garden, the umbrella thorn's branching root system is efficient for stabilizing eroded banks and hillsides and its dense rootlets will help with catching silt to rebuild topsoil (however, keep it away from paved areas and buildings!). The inner bark has medicinal uses and can also be used to make rope. Green seed pods contain trace amounts of hydrocyanic acid, however some animals have developed immunity and readily feed from the tree, including baboons, vervet monkeys and parrots. When the stems are injured, a sweet resin leaks from the wounds and provides a tasty treat for children. 

Like most acacias, the umbrella thorn also makes a popular bonsai!





Cultivation: 

Umbrella thorn is easily grown from seed. Seeds should be immersed in hot water and left to soak overnight. Plant in the morning and cover with a shallow layer of soil. The seedlings form a very long taproot so they must be permanently planted once the first leaf has formed (be careful when transplanting!). It is frost and drought-resistant and grows approximately half a meter per year. If you wish to speed up its growth you can cut away the lower branches.

Sources 
  1. Making the most of Indigenous Trees, Fanie and Julye-Anne Venter
  2. Trees and Shrubs of Mpumalanga and Kruger National Park, Ernst Schmidt, Mervyn Lotter and Warren McClealand

*If you're a botanist (or from Australia) you might know there's currently quite an uproar over the taxonomy of African vs Australian acacias. Please know I am forever for Team Africa and will call these trees acacias till my dying days.
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