Acacia karroo (Hayne) Family: Fabaceae Sub family: Mimosoideae
Common names: Sweet thorn (English); Soetdoring (Afrikaans); Mookana (North Sotho); Mooka (Tswana); umuNga
(Zulu) (Xhosa)
SA tree number: 172 Description: The tree grows up to 15 m in height, with rough, dark, red-brown to blackish bark.
The trunk is usually branched relatively close to the ground.
Paired and straight conspicuous white spines occur, especially on the lower branches and on
younger trees or trees being browsed by animals although some forms are almost thornless as
adults.
Trees often flower after rain and are usually in full flower in spring and early summer. The flowers
are arranged in heads and exude a sweet scent.
The slender, sickle-shaped pods split open from January onwards releasing small, hard seed.
Distribution: Distributed throughout southern Africa in habitats ranging from desert to
floodplains, mountain tops to grasslands and river mouths. Replaced by Acacia seyal north of the
Zambezi river. Name derivation: The name Acacia is derived from the Greek word 'akis', meaning a point,
referring to the thorns found on African Acacia species. All South African species are armed with
thorns, although their shape can vary.
“Karroo” is the old spelling for Karoo, where the species was first described by botanical
explorers.
The sweet thorn gets its English and Afrikaans common names from the gum which is exuded
from wounds in the bark. This gum is edible and sweet tasting.
Ecology and uses: Flowers attract bees in search of pollen and nectar. Many other insects are
attracted to the tree as well and, consequently, also birds, lizards and snakes. This species is
also the host tree for several butterfly species.
The presence of the tree is considered by farmers as an indicator of “sweet” veldt and water; it is
also considered an extremely good fodder tree.
The inner bark contains tannins and has been used to tan leather; it can also be used to make
rope. The pleasant tasting gum exuded from the tree is eaten by people and animals, and historically
also had commercial value when the gum was exported as "Cape Gum" for making
confectionary.
Cultivation: Acacia karroo is a must for the garden although it has a relatively short life span for
a tree, thirty to forty years on average. Seeds germinate best if soaked in hot water for a few
hours.
It grows rapidly in any soil and in any climate found in Sotuh Africa, flowering from 2-3 years of
age.
This is probably southern Africa's most common tree, it occurs in many different habitats and in
many different forms.
Notes: The third edition of Trees of Southern Africa by K. Coates Palgrave and M. Coates
Palgrave cites four new species derived from the “Karroo-complex” as described by P. P. Swartz .
Also A. natalitia, the “KZN-form of A. karroo”, often showing a pale to whitish bark, was reinstated
in the same volume.
There are now the following six species/varieties in the A. karroo-complex, although it should be
said that many traits used in defining the “new” species do intergrade into each other and it is
possible to find specimens of trees showing a combination of characteristics, this is especially
true regarding “typical” A. karroo versus A. natalitia:
A. dyeri: a shrub with many stems originating from the root system, less than 1m in height,
endemic to the grass-veld of Kei River Mouth area north of East London.
A. karroo: a tree, although usually branching very close to the ground. It has 2-3(max.5) pair of
pinnae and usually dark grey/black to reddish bark. Leaflets are usually dark green in colour. SA
tree number: 172
A. kosiensis: 10-17m high, yellow powder-puff inflorescence hidden among the leaves;
extremely long thorns and thorns often persistent on trunk, rachis and rachillas are finely hairy,
but leaflets are without hairs and a bright, fresh green in colour. Trees are usually very tall and
upright with flat crowns. Occurs along KZN-coast north of the Tugela River to Mozambique,
usually growing as a pioneer in sand-forest at very high densities in developing woodland. Bark is
an unusual pale grey. SA tree number: 172.2
A. theronii: (described in Palgrave et. al. as A. montana) 4-6- m high, flowers and ripe pods
together on tree. Known as the "spindle form" of A. karroo previously as the tree shape is
etoliated with few branches. SA tree number: 172.3
A. robbertsei: 6 or more pair of pinnae; all parts of the compound leaf and pods are densely
hairy. It must be said that this entity seems the end point of a trend that begins in Pretoria and
increases as one progresses east, reaching a maximum in Sekhukhuneland. SA tree number:
172.4
A. natalitia, pale to white-barked tree or shrub with short spines and 4 - 13 pinna pairs per leaf,
mainly found in the Eastern Cape, KZN, Swaziland, Mpumalanga, Zimbabwe and Mozambique.
SA tree number: 172.1
This is by no means the final word in the complex as many different forms await investigation as
the species is extremely variable across its range.
The Botanical Garden is trying to put together a reference collection of these named
species/varieties and will post new acquisitions on the website as we obtain them. Currently we
have A. kosiensis and the central Free State form of A. karroo as habitat collected seed and
seedlings plus numerous Pretoria type adult plants in the Garden.
It is best to plant the form of Acacia karroo found in your own area as this will be adapted to the
climatic and environmental conditions found there.
Found in Section L of the Map
References:
• Carr, J.D., 1976. The South African Acacias. Published by Conservation press.
Johannesburg. (Currently out of print).
• Coates Palgrave, K. & Coates Palgrave, M. 2002. Keith Coates Palgrave’s trees of
southern Africa edn 3. Struik, Cape Town.
• Joffe, P. 2001. Creative gardening with indigenous plants - a South African guide. Briza
Publications, Pretoria.
• Smit, N., 1999. Guide to the Acacias of South Africa. Briza Publications, Pretoria.
• Van Wyk, B. & Van Wyk, P. 1997. Field guide to the trees of southern Africa. Struik, Cape
Town.
• Van Wyk, B., van den Berg, E., Coates Palgrave, M. & Jordaan, M. 2011. Dictionary of
names for southern African trees. Briza Publications, Pretoria.
• Venter, F. and Venter, J. 1996. Making the most of indigenous trees. Briza Publications,
Pretoria.
Web Resources:
The Acacia World website, “The Karroo Complex”,
http://www.acacia-world.net/html/the_karroo-complex.html. Site accessed 18/01/2011.
South African National Biodiversity Institute website, “Plants of South Africa”.
http://www.plantzafrica.com/frames/plantsfram.htm. Site accessed 18/01/2012.