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When most hear the name acacia they think of the umbrella thorn acacia – the typical picture of Africa. But the genus Acacia is the largest group of woody trees and shrubs in the subfamily Mimosoideae f the family Leguminosae (or bean family). The 132 species in Africa are mostly restricted to the dry savannah and semi-desert.  Acacias play an important rule in nature. They provide food for wild animal and livestock as well as materials for local people. All pod-bearing plants have nodules on their roots which contain nitrogen-fixing bacteria. This maintains the fertility of soil. The tiny leaflets in most acacias reduce evaporation. Sometimes you see a greenish colour on the stem and on branches. This is chlorophyll. That is how they enlarge the surface to do photosynthesis. The different species have different preferences and therefore grow in different biotopes.

When acacias get stressed because of draught and over browsing they produce prussic acid, which can be fatal. That is not enough, acacias communicate by chemicals when it is time to become poisonous to defend themselves.

Photos by Elvira

 

 

Flat-top acacia (Acacia abyssinica). Nice individuals can be seen in Nakuru National park and on the way to Bogoria and Masai Mara.

Acacia_abyssinica

 

 

Floetenakazie
Floetenakazie_Ameisen

 

 

Whistle thorn or Ant-galled acacias (Acacia drepanolobium) are short shrubs in the Rift valley, Masai Mara and Serengeti. When the wind blows into the holes of these for ants built galls you hear a whistling sound and this gave them their name.

These enlarged and hollow thorns are shelters and breeding place for the Acacia-ants of the genus Crematogaster and Tetraponera. That is not yet enough, the acacia feeds the ants with a sugary sap and a highly nutritious snack. In return the ants defend the tree against hungry insects and herbivores by biting them and spraying a bad odour. This co-existence is called Myrmecophily and exists in the new and old world.

Spiders and hunting beetles feed on the ants. 

 

 

 

 

Acacia_gerrardi

 

Acacia gerrardi Blueten

 

 

 

 

Gerrard's acacia (Acacia gerrardi) grow to large trees. Thorns are quite thick and grow in pairs. The leaves have a dull green and are tiny. The flowers
are whitish balls and the bark on the stem is almost black. Nice individuals stand in Nakuru and on the way to Lake Magadi as well as in Kiambu region.

 

 

 

 

Acacia_kirkii

 

 

Kirk’s Acacia (Acacia kirkii) grows around Nairobi, Northern Uganda
and Northern Tanzania. The bark is often papery and peels off.

 

 

Hook-thorn acacia (Acacia mellifera) has bigger leaves than most other acacias in Kenya, which makes it easy to recognize it. The thorns are nasty when you get too close and that is why it got its other name “wait-a-bit-bush”. Buds, flowers and seeds showed on the pictures. Pods, leaves, flowers and twigs are much favoured by game and stock. Mellifera refers to the flowers containing a lot of nectar and means “honey bearing”. Hollow tree trunks are hanged in trees as bee-hives so the locals can harvest tasty acacia honey.
 

Acacia_mellifera_Blueten
Acacia_mellifera_Samen

 

 

Acacia_nil_subalata

Acacia_nilotica_indica

 

 

Egyptian thorn or Scented-pod acacia (Acacia nilotica subalata). This subspecies is indigenous to Kenya and Tanzania. The pods are flatter. When you break them a nice smelling sap flows out. The ripe pods turn brown.

Egyptian thorn or Scented-pod acacia (Acacia nilotica) have very characteristic pods. Without them they are not easy to be identified.

The subspecies indica is introduced to Baringo District from India. The pods are rounder. Picture taken at Lake Bogoria.

 

 

Acacia_senegal

Acacia_brevispica

 

 

Sudan gum arabic or Three-thorned acacia (Acacia senegal) has 3 hooks below each node; outer 2 curve upward and the centre hook curves downward. It takes you time to free your cloths once they hang in the thorns....  Leaves and pods are rich in protein. Wide spread in tropical Africa.

 

 

Wait-a-bit-thorn (Acacia brevispica). Spread from Central Kenya, Rift valley to Northern Tanzania. The thorns are hooks or prickles with sharp reddish tips. Picture from  Lake Bogoria.

 

 

Acacia_seyal_fungi

 

Acacia_seyal_seyal

 

 

 

 

White-thorn acacias (Acacia seyal) have conspicuous 8 cm long spines. Similar the Whistle-thorn acacia they build galls in which ants live. These ants defend the tree against insects and herbivores. The yellow flowers provide nectar for bees.  In Meru National park and Lewa Downs you find the subspecies fistula and in Nakuru and Tanzania seyal without galls.

The brown colour on the stem and branches are fungi. Picture is taken in Lewa Conservancy.

 

Acacia seyal, var. seyal without galls in the Masai Mara. Good to see are the fruits and bright yellow flowers.

 

 

 

 

 

 

Umbrella thorn (Acacia tortilis) are most likely those trees creating the image of Africa with their large umbrellas providing shade to the trunk and roots. Beside small hooked thorns they also have straight  3-8 cm long, whitish thorns which even puncture shoe soles. The 2 kind of thorns should reduce the browsing by giraffes. The pods for a spiral and are eaten by all kind of animals.

Umbrella thorn grows in many dry areas Africa’s.

Acacia_tortilis
Acaia_tortilis_Ast

 

 

Apfelringakazie
Gelbrindenakazien

 

 

Apple-ring Acacia (Faidherbia albida) is one of the tallest acacias in subtropical Africa. The fruits look like dried apple rings and are eaten by baboons and other animals. The flowers are yellowish white coloured spikes. It occurs in Kenya and Tanzania.

 

Yellow-barked acacia (Acacia xantophloea) are dominant in Naivasha and Nakuru. They need a relatively high underground water level. It is called fever tree because mosquitoes occur where they grow and it has substances in its bark to cure malaria. Various animals feed on the sap many acacia trees produce. Who looks at the picture carefully will see the lioness in the middle.

 

 

 

Albizia_gummifera

 

Peacock flower (Albizia gummifera) is in the same subfamily than acacias. They grow from sea level to 2400 m and can become very large trees.