African Wildlife & Environment Issue 83

FAUNA, FLORA & WILDLIFE

blast (a shoot of limited growth/short-shoot/ axillary bud). Looking at many trees I think these short-shoots can be active for 5+ years, producing leaves annually on branches that can, in rare cases, even be ~50mm diameter. What a wonderful adaptation! And in poor years there may even be NO new growth and thus NO primary leaves! This would be unusual for KNP (except in a DROUGHT year) but more usual for the Karoo. Note that on THIS primary leaf (left) there are extra flora nectaries (ENFs) on the petiole & rachis (circled) – this is not always the case (the petiolar ENF is most often oblong rather than round, but can also be round like the rest on the rachis – so VARIABILITY). Another consideration may be that in wetter areas there are more ENFs on primary leaves, and in more arid areas fewer, if any (and often then just the one on the petiole). The same goes for ENFs on secondary leaves, none in arid areas but maybe one or more in wetter areas. Occasionally in wetter areas there can even be the odd ENF on the petiole of secondary leaves – but then small (possibly vestigial?). THUS all quite complicated – so we

Of particular significance is that in many of the species, where I have observed primary and secondary leaves, they have a recognisably different morphology. Yet in many of the descriptions of these species the authors simply describe leaf variation sensu lato - and lump the morphology of these two DIFFERENT leaf-types into one generalized description. No wonder many amateurs find some trees difficult to identify, when the ‘experts’ themselves have lumped two leaf types into one; that in many cases can be fairly easily separated if one observes carefully! The three, composite photographs below of A. karroo PRIMARY and SECONDARY leaves, with their individual features highlighted and an explanation, is what you should be observing and thinking about. These images demonstrate the complex nature of their morphology that relates to their function and evolution. Possibly it is no wonder that these details have not been highlighted in various references and texts on the species. Below a PRIMARY leaf (on a shoot of UNLIMITED growth that you cannot fully see in this photo), and right a bunch of SECONDARY leaves on a brachy

must decide on how much detail we are going to give? What is good is if we explain in detail for one acacia we can then refer to this for the others where the SAME thing can happen – even if this is never quite the same. Plants are modular!

26 | African Wildlife & Environment | Issue 83 (2023)