Flowering Trees

© Roger de la Harpe
Acacia Tree flowers.

After this welcome period of rain, in a season that is predicted to be hot and dry, many of the later flowering plants are out in full bloom. While searching for the big five it is easy to overlook the smaller marvels of nature, particularly those that don't move.

Larger trees in full colour are hard to miss. Many trees have already flowered and are bearing new seed pods among the foliage. Most notable of these are the 'Sjambok pod' - Cassia abbreviata,with it's long, hanging pods and bright green foliage. The 'Transvaal teak' - Pterocarpus angolensis - with it's corky bark and green 'fried egg' shaped pods, had an early bloom of yellow flowers.

At present, a smaller but related tree, the 'Round-leaf teak' - Pterocarpus rotundifolius - is starting to produce showy bunches of yellow blooms which will continue, at opportune moments, for a few weeks. Baobabs - Adansonia digitata - have already flowered, although there may be some late blooms, and have started forming small green, sperical fruit.

Their large white flowers are cross pollinated by bat species and the fruit-bearing success can be an indicator of the health of the bat population in the area and, possibly, the presence of other baobabs in the vicinity.  As a matter of interest, the lone baobab just south of Satara Camp in the Kruger National Park marks the southerly extent of natural distribution of baobabs in Africa. There are some planted specimens further south - even in the Cape.

There are over seventy species of Acacia (Thorn Trees) in southern Africa. Some of them flowered early in the season, like the 'Knobby Thorn' - Acacia nigrescens - which, this season, had it's best flowering season in the last twenty years. Many of you will have noticed the prolific show of cream coloured 'spikes' that covered the trees in October. 

You may not have noticed that some individuals of that species started with reddish buds while others had lime green buds, giving them either a buff or lime colour respectively.  Many of our trees have this variability. The 'Wild Pear' - Dombeya rotundifolia - is another example, with normally cream but sometimes pink flowers that are produced early in the season.  The 'Lucky-bean Trees' - Erythrina spp.- with their very striking scarlet blooms are another species that flowers early.

You will notice that most of the trees produce their flowers before the leaves appear.  This is ensures that the colour of the blooms has maximum attraction to insects and birds, unhindered by foliage, which follows shortly after pollination has taken place. 

Where the scent attraction is more important than colour, you will notice that the small, cream or white flowers have a pungent scent to attract moths and other, often nocturnal, insects and that the flowers and leaves are produced together.  This may have some benefit in protecting the small, vulnerable flowers from wind. Many of the trees in this category belong to the Combretum spp. and the Terminalia spp. You will note the pungent smell as you travel around particularly in the evenings.

To return to the Acacias - there are several factors that one should look for in trying to identify the species.  Flowers are borne either as 'spikes' or fingers, or else as 'balls' or spheres.  The spikes are always white or cream coloured but the balls can be white or bright yellow. Check what type of flowers the tree has. 

A feature of Acacias are the thorns which are either straight or hooked, sometimes both on the same plant. The hooks can be single, paired or in threes while the straight ones are normally paired. On certain species the thorns are very small and hardly noticeable. Often the straight thorns are 'galled' by insects (normally wasps or beetles) which lay their eggs in them, causing them to become very enlarged. Some species have 'knob' thorns attached to the bark on the trunks of young trees as a protection. These knobs are absent in most adult trees.

 One should be aware that this feature also occurs on the stems of other genera. Thorns are like 'finger nails' and do not support leaves while Spines, which occur on similar looking genera, are woody branches with a spike at the end, which often have leaves growing from them. Being 'woody', spines will puncture vehicle tyres whereas thorns will rarely do so.

The leaves of all Acacias are bi-pinnate or bi-compound - 'jacaranda like' - except in the case of Acacia nigrescens, Acacia burkeii and some others, where the sub-leaflets are larger. The coarseness of the leaf can be used as an identifying feature but it a difficult one for the inexperienced.

Be aware that many other plants also have the 'jacaranda' type leaves although they are completely separate genera. Examples are Peltophorum africanum (Wild Wattle) with the droops of profuse yellow-petalled flowers, that are quite a show at the moment, and the 'Sickle Bush' or Dichrostachys cinerea which normally grows in thickets on disturbed areas and has the pink/white and yellow 'Chinese Lantern' flowers.

Many of the Acacias that are presently in flower. Along the river lines most species have white flowers. The large trees with white 'balls' are likely to be Acacia robusta (Brak thorn) while the tangled, creeper-like hook-thorns are Acacia ataxacantha if they have white spikes and Acacia schweinfurthii if they have white balls.  Away from the riverine areas, the Acacia tortillis has profuse tiny white balls at the moment, making a very attractive show.

A smallish Acacia with larger white balls clumped along the branches is Acacia gerrardii.  The attractive ones with yellow balls are Acacia nilotica and Acacia karroo. There are too many to try and describe in a short article but with a good tree book and intelligent observation you should be able to make some identifications of your own.

While looking at the flowering trees, instead of for the 'Big Five', don't forget to look lower down. In the areas with diminished competition from grass you will see many small flowering plants or 'forbs'. Clumps of mauve/blue (sometime yellow) Barlaria spp., multi headed Senecio spp., single heads of bright scarlet Kleinia fulgens or bunched Crossandra spp.  The mauve/red plants with small bean pods are probably an Indigofera sp. while the taller ones with yellow flowers are probably Crotalaria sp.

The array is never ending.  You will need a good flower book and a pair of binoculars if you are in the parks and don't want to be caught out of your vehicle. Your progress will be slow but you will find it infinitely more interesting than staring at a pride of sleeping lions. Many of these plants are not found any more in areas subject to agriculture and herbicides. The benefit of going slowly and looking at the little things is that you are far more likely to spot the big things as well.

Dave Rushworth

Africa Tree Guide

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Kruger National Park - South African Safari