Acacia karroo is the most widespread acacia species in Southern Africa. On the other hand it seems, that in the past all plants that looked more or less like Acacia karroo were put under this roof. J.D. Carr describes a typical form and five variants. N. Smit in his 1999 Guide to the Acacias of Southern Africa describes a lot of variations linked to the “central A. karroo gene-pool”.

In 2002 P.P. Swartz divided the group into four subspecies, published in “Trees of Southern Africa” by Meg Coates Palgrave (ed) 3rd edition , ISBN 1868723895.

There were some name changes finally leading to the following five species in the
A. karroo complex:

Acacia dyeri

Acacia karroo

Acacia kosiensis

Acacia robbertsei

Acacia theronii

  Gums are secreted at wounds

Some explanations how to differentiate them are given by Eileen Campbell in the newsletter 4th Quarter 2003 of the Algoa Branch of the Botanical Soc. of South Africa, (www.botanicalsociety.org.za ).

Analysing her article I distill out the characteristics for:

A. karroo: is a tree, although branching very close to the ground. It has 2-3 pair of pinnae
A. kosiensis: yellow powder-puff inflorescence hidden among the leaves; rachis and   rachillas are finely hairy, but leaflets are without hairs.
A. theronii: flowers and ripe pods together on tree.
A. dyeri: a shrub with many stems originating from the root, always shorter than 1m, endemic to the grass-veld of Kei River Mouth area north of East London.
A. robbertsei: 6 or more pair of pinnae; all parts of the compound leaf are densely hairy.

J. Hurter considers also A. natalitia a separate species in the karroo complex. It is described by N. Smit as a white-barked tree or shrub with short spines and 4 - 13 pinna pairs per leaf.

Considering these new definitions, the distribution of A. karroo sens. strict. in South Africa will have to be redefined.