The Acacia karroo-complex

In his 1976 book The South African Acacias, J.D. Carr notes that “ the species varies considerably in overall appearance, size and other characters and the layman may be justified in expressing surprise that the differences have not been considered sufficiently marked to warrant division into subspecies, or at least varieties.”

Regarding the foliage he writes: “Typical” pinna pairs number generally from 3 to 5, but 12 and even 16 have been noted from the N. and E. Transvaal these latter possibly coming from a further variant. The book shows a picture of an A. karroo leaf from the Barberton district with more than 7 pairs of pinnae.

The 1999 Guide to the Acacias of South Africa by Nico Smit still keeps Acacia karroo as one species, but talks of a gene-pool and mentions several “untypical” forms.

In 2002 the third edition of Trees of Southern Africa by M. Palgrave cites four new species derived from the Karroo-complex as described by P.P.Swartz , three of which received tree numbers by the Dendrological Society of South Africa ( only A. dyeri is missing in that list). Also A. natalitia, the “KZN-form of A. karroo”, often showing a whitish bark, was reinstated  and got its own tree-number.

There are now the following six species/varieties in the A. karroo-complex:

Acacia dyeri
Acacia karroo
Acacia kosiensis
Acacia natalitia
Acacia robbertsei
Acacia theronii (initially named A. montana by P.P.Swartz)

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 distinguishing characteristics for:

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. karroo: is a tree, although branching very close to the ground. It has 2-3(max.5) pair of pinnae

A. kosiensis: 10-17m high, yellow powder-puff inflorescence hidden among the leaves; rachis and rachillas are finely hairy, but leaflets are without hairs. Along KZN-coat north of Tugela River to Mocambique

A. theronii: 4-6- m high, flowers and ripe pods together on tree.

A. robbertsei: 6 or more pair of pinnae; all parts of the compound leaf are densely hairy.

A. natalitia, described by N. Smit as a 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 Mocambique.

A. karro s.s. is limited to a maximum of 5 pair of pinnae. That leaves the tall Acacia karroo-trees with more than 6 pairs of pinnae, described by Carr, shown in the literature or on the internet and often found in South Africa and Namibia, i.e. in other areas than described above, without a name. I suggest a broader genomics study of this group - as is actually been done with the very difficult group of A.aneura (Mulga) in Australia by. J. Miller et.al.