African Wildlife & Environment Issue 80

FAUNA, FLORA & WILDLIFE

laboratory. Typically, A. karroo has two basic shoot types – shoots of UNLIMITED GROWTH that can be recognised by the fact that the bark on the twigs is still green, where there is just one leaf per node (exactly between the young, stipular spines), and by other features that are shown in the photograph and noted in the caption. The second shoot type is produced from the axillary bud(s) in the axils of the primary leaf, generally on older twigs where the bark has hardened and is brownish in colour. These are termed SHOOTS OF LIMITED GROWTH. In the field these can be easily recognised as they

what we know as a 'lumper' in the taxonomic world. However, since then the 'splitters' have been at work and what he described as A. karroo has been split into several 'new' species. One is the coastal form (occurring from north of Durban into Mozambique), where the trees can be much bigger and spines as long as 320 mm have been recorded; this is now A. kosiensis. Another variant, with whitish bark, is now known as A. natalitia, and the spindle growth-form, confined to the Hluhluwe-Mfolozi Complex, as A. theronii.

Figure 14. A bunch of five SECONDARY LEAVES produced from an axillary bud known as a brachyblast (a shoot of LIMITED growth)

Figure 13. A PRIMARY LEAF attached between two stipular spines on a shoot of unlimited growth

Morphological complexities of Acacias - using A. karroo as the example What Ross taught me long ago was that many Acacias have two types of shoots.What I have discovered in the last few years is that many other bushveld trees also have these two shoot types. The significance of this seems to have escaped all the taxonomists, and if there is any mention of them in all the tree-books I have read, this is only in passing. I find this omission incomprehensible, simply because the leaves on these shoot types differ significantly morphologically. Even Jim Ross, who taught me about these, did not incorporate this information in his Flora account! Over time I have assembled a photographic record of many species of Acacias , looking specifically at their different shoot types.The results are astonishing. Lately I have studied the shoots of what I think are typical specimens of A. karroo by removing many branches from a few adjacent individuals, and then investigating the leaf morphology carefully in the

Figure 15. Showing BOTH a primary leaf (above) and two secondary leaves below

form a bunch of anything from 2-10 leaves, that all arise from a seemingly central point at the node. These shoots of limited growth arise from what we

20 | African Wildlife & Environment | Issue 80 (2021)