African Wildlife & Environment Issue 80

FAUNA, FLORA & WILDLIFE

Figure 17. The bright yellow pom pom-like inflorescences on a shoot of unlimited growth.

Figure 16. Trees in almost full flower

Figure 18. Ripe pods with seeds still attached by a thread - waiting to be shaken off

Figure 19. Rapid resprouting after fire is a great survival strategy

Palgrave (1977) that I edited! Some ecological considerations

botanists call brachyblasts. From my observations, shoots of limited growth can produce leaves annually for at least 4-6 years (so in a seasonally bad year, when the tree is unable to grow new shoots, these secondary leaves are critical for photosynthesis). One of the morphological differences between the primary and secondary leaves is that the extra floral nectary (EFN) on the leaf petiole, and sometimes also along the rachis (=main axis), is mostly present on primary leaves and mostly absent on secondary leaves . In addition, the number of pinna pairs on secondary leaves ranges from 2-5, while on primary leaves there are usually at least 3-5 pairs and occasionally more. What this means is that it is possible, presented with just one leaf, to say with a large degree of certainty whether the leaf is primary or secondary. Yet in the description in the Flora , Ross simply says that the ENF is usually present or absent, and that the leaves have 1-2 to 6-13 pinna pairs. Clearly, by lumping the features, he is not separating primary from secondary leaves. Such lumping is also done by the authors of tree books including the first edition of Coates

For me Vachellia karroo is our most widespread and most numerous South African tree. It could, and perhaps should have been our National Tree? However, it is not only confined to South Africa as it extends further north into Angola, Zambia and Mozambique. It is essentially a southern African species. Certainly, from the work of Timm Hoffman, its occurrence in the karoo has increased geographically in the last 100 years; moving much further west along drainage lines, as well as increasing in density. As the trees have moved westwards, kudu and vervet monkeys have followed this spread. From the work of Bruce Campbell, the trees on Signal Hill are most likely natural, although there is also an opinion that they may well have been planted several hundreds of years ago. Maybe we will never know the truth! The species has many growth forms .Typically, the rounded canopy form with a main trunk is for me

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